29. Data and instructions
Now it’s time to look more closely at the work of the CPU. After all, what does it actually do?
Instructions and data
Our CPU processes instructions and data. It receives orders from the software. The CPU is fed a gentle stream of binary data via the RAM.
These instructions can also be called program code. They include the commands which you constantly – via user programs – send to your PC using your keyboard and mouse. Commands to print, save, open, etc.
Data is typically user data. Think about that email you are writing. The actual contents (the text, the letters) is user data. But when you and your software say “send”, your are sending program code (instructions) to the processor:
Figure 80. The instructions process the user data.
Instructions and compatibility
Instructions are binary code which the CPU can understand. Binary code (machine code) is the mechanism by which PC programs communicate with the processor.
All processors, whether they are in PC’s or other types of computers, work with a particular instruction set. These instructions are the language that the CPU understands, and thus all programs have to communicate using these instructions. Here is a simplified example of some “machine code” – instructions written in the language the processor understands:
proc near
mov AX,01
mov BX,01
inc AX
add BX,AX
You can no doubt see that it wouldn’t be much fun to have to use these kinds of instructions in order to write a program. That is why people use programming tools. Programs are written in a programming language (like Visual Basic or C++). But these program lines have to be translated into machine code, they have to be compiled, before they can run on a PC. The compiled program file contains instructions which can be understood by the particular processor (or processor family) the program has been “coded” for:
Figure 81. The program code produced has to match the CPU’s instruction set. Otherwise it cannot be run.
The processors from AMD and Intel which we have been focusing on in this guide, are compatible, in that they understand the same instructions.
There can be big differences in the way two processors, such as the Pentium and Pentium 4, process the instructions internally. But externally – from the programmer’s perspective – they all basically function the same way. All the processors in the PC family (regardless of manufacturer) can execute the same instructions and hence the same programs.
And that’s precisely the advantage of the PC: Regardless of which PC you have, it can run the Windows programs you want to use.
Figure 82. The x86 instruction set is common to all PC’s.
As the years have passed, changes have been made in the instruction set along the way. A PC with a Pentium 4 processor from 2002 can handle very different applications to those which an IBM XT with an 8088 processor from 1985 can. But on the other hand, you can expect all the programs which could run on the 8088, to still run on a Pentium 4 and on a Athlon 64. The software is backwards compatible.
The entire software industry built up around the PC is based on the common x86 instruction, which goes back to the earliest PC’s. Extensions have been made, but the original instruction set from 1979 is still being used.
x86 and CISC
People sometimes differentiate between RISC and CISC based CPU’s. The (x86) instruction set of the original Intel 8086 processor is of the CISC type, which stands for Complex Instruction Set Computer.
That means that the instructions are quite diverse and complex. The individual instructions vary in length from 8 to 120 bits. It is designed for the 8086 processor, with just 29,000 transistors. The opposite of CISC, is RISC instructions.
RISC stands for Reduced Instruction Set Computer, which is fundamentally a completely different type of instruction set to CISC. RISC instructions can all have the same length (e.g. 32 bits). They can therefore be executed much faster than CISC instructions. Modern CPU’s like the AthlonXP and Pentium 4 are based on a mixture of RISC and CISC.
Figure 83. PC’s running Windows still work with the old fashioned CISC instructions.
In order to maintain compatibility with the older DOS/Windows programs, the later CPU’s still understand CISC instructions. They are just converted to shorter, more RISC-like, sub-operations (called micro-ops), before being executed. Most CISC instructions can be converted into 2-3 micro-ops.
Figure 84. The CISC instructions are decoded before being executed in a modern processor. This preserves compatibility with older software.
Extensions to the instruction set
For each new generation of CPU’s, the original instruction set has been extended. The 80386 processor added 26 new instructions, the 80486 added six, and the Pentium added eight new instructions.
At the same time, execution of the instructions was made more efficient. For example, it took an 80386 processor six clock ticks to add one number to a running summation. This task could be done in the 80486 (see page 40), in just two clock ticks, due to more efficient decoding of the instructions.
These changes have meant that certain programs require at least a 386 or a Pentium processor in order to run. This is true, for example, of all Windows programs. Since then, the MMX and SSE extensions have followed, which are completely new instruction sets which will be discussed later in the guide. They can make certain parts of program execution much more efficient.
Another innovation is the 64-bit extension, which both AMD and Intel use in their top-processors. Normally the pc operates in 32-bit mode, but one way to improve the performance is using a 64-bit mode. This requires new software, which is not available yet.
30. Inside the CPU
Instructions have to be decoded, and not least, executed, in the CPU. I won’t go into details on this subject; it is much too complicated. But I will describe a few factors which relate to the execution of instructions. My description has been extremely simplified, but it is relevant to the understanding of the microprocessor. This chapter is probably the most complicated one in the guide – you have been warned! It’s about:
If we continue to focus on speeding up the processor’s work, this optimisation must also apply to the instructions – the quicker we can shove them through the processor, the more work it can get done.
Pipelines
As mentioned before, instructions are sent from the software and are broken down into micro-ops (smaller sub-operations) in the CPU. This decomposition and execution takes place in a pipeline.
The pipeline is like a reverse assembly line. The CPU’s instructions are broken apart (decoded) at the start of the pipeline. They are converted into small sub-operations (micro-ops), which can then be processed one at a time in the rest of the pipeline:
The pipeline is made up of a number stages. Older processors have only a few stages, while the newer ones have many (from 10 to 31). At each stage “something” is done with the instruction, and each stage requires one clock tick from the processor.
Modern CPU’s have more than one pipeline, and can thus process several instructions at the same time. For example, the Pentium 4 and AthlonXP can decode about 2.5 instructions per clock tick.
The first Pentium 4 has several very long pipelines, allowing the processor to hold up to 126 instructions in total, which are all being processed at the same time, but at different stages of execution (see Fig. 88. It is thus possible to get the CPU to perform more work by letting several pipelines work in parallel:
CPU
|
Instructions executed
at the same time |
AMD K6-II
|
24
|
Intel Pentium III
|
40
|
AMD Athlon
|
72
|
Intel Pentium 4
(first generation) |
126
|
Figure 88. By making use of more, and longer, pipelines, processors can execute more instructions at the same time.
The problems of having more pipelines
One might imagine that the engineers at Intel and AMD could just make even more parallel pipelines in the one CPU. Perhaps performance could be doubled? Unfortunately it is not that easy.
It is not possible to feed a large number of pipelines with data. The memory system is just not powerful enough. Even with the existing pipelines, a fairly large number of clock ticks are wasted. The processor core is simply not utilised efficiently enough, because data cannot be brought to it quickly enough.
Another problem of having several pipelines arises when the processor can decode several instructions in parallel – each in its own pipeline. It is impossible to avoid the wrong instruction occasionally being read in (out of sequence). This is called misprediction and results in a number of wasted clock ticks, since another instruction has to be fetched and run through the “assembly line”.
Intel has tried to tackle this problem using a Branch Prediction Unit, which constantly attempts to guess the correct instruction sequence.
Length of the pipe
The number of “stations” (stages) in the pipeline varies from processor to processor. For example, in the Pentium II and III there are 10 stages, while there are up to 31 in the Pentium 4.
In the Athlon, the ALU pipelines have 10 stages, while the FPU/MMX/SSE pipelines have 15.
The longer the pipeline, the higher the processor’s clock frequency can be. This is because in the longer pipelines, the instructions are cut into more (and hence smaller) sub-instructions which can be executed more quickly.
CPU
|
Number of
pipeline stages |
Maximum clock frequency
|
Pentium
|
5
|
300 MHz
|
Motorola G4
|
4
|
500 MHz
|
Motorola G4e
|
7
|
1000 MHz
|
Pentium II and III
|
12
|
1400 MHz
|
Athlon XP
|
10/15
|
2500 MHz
|
Athlon 64
|
12/17
|
>3000 MHz
|
Pentium 4
|
20
|
>3000 MHz
|
Pentium 4 „
|
31
|
>5000 MHz
|
Figure 89. Higher clock frequencies require long “assembly lines” (pipelines).
Note that the two AMD processors have different pipeline lengths for integer and floating point instructions. One can also measure a processor’s efficiency by looking at the IPC number (Instructions Per Clock), and AMD’s Athlon XP is well ahead of the Pentium 4 in this regard. AMD’s Athlon XP processors are actually much faster than the Pentium 4’s at equivalent clock frequencies.
The same is even more true of the Motorola G4 processors used, for example, in Macintosh computers. The G4 only has a 4-stage pipeline, and can therefore, in principle, offer the same performance as a Pentium 4, with only half the clock frequency or less. The only problem is, the clock frequency can’t be raised very much with such a short pipeline. Intel have therefore chosen to future-proof the Pentium 4 by using a very long pipeline.
Execution units
What is it that actually happens in the pipeline? This is where we find the so-called execution units. And we must distinguish between to types of unit:
If the processor has a brain, it is the ALU unit. It is the calculating device that does operations on whole numbers (integers). The computer’s work with ordinary text, for example, is looked after by the ALU.
The ALU is good at working with whole numbers. When it comes to decimal numbers and especially numbers with many decimal places (real numbers as they are called in mathematics), the ALU chokes, and can take a very long time to process the operations. That is why an FPU is used to relieve the load. An FPU is a number cruncher, specially designed for floating point operations.
There are typically several ALU’s and FPU’s in the same processor. The CPU also has other operation units, for example, the LSU (Load/Store Unit).
An example sequence
Look again at Fig. 73. You can see that the processor core is right beside the L1 cache. Imagine that an instruction has to be processed:
This description applies to the working cycle in, for example, the Pentium III and Athlon. As a diagram it might look like this:
But the way the relationship between the pipeline and the execution units is designed differs greatly from processor to processor. So this entire examination should be taken as a general introduction and nothing more.
Pipelines in the Pentium 4
In the Pentium 4, the instruction cache has been placed between the “Instruction fetch/Translate” unit (in Fig. 90 and the ALU/FPU. Here the instruction cache (Execution Trace Cache) doesn’t store the actual instructions, but rather the “half-digested” micro-ops.
The actual pipeline in the Pentium 4 is longer than in other CPU’s; it has 20 stages. The disadvantage of the long pipeline is that it takes more clock ticks to get an instruction through it. 20 stages require 20 clock ticks, and that reduces the CPU’s efficiency. This was very clear when the Pentium 4 was released; all tests showed that it was much slower than other processors with the same clock frequency.
At the same time, the cost of reading the wrong instruction (misprediction) is much greater – it takes a lot of clock ticks to fill up the long assembly line again.
The Pentium 4’s architecture must therefore be seen from a longer-term perspective. Intel expects to be able to scale up the design to work at clock frequencies of up to 5-10 GHz. In the “Prescott ” version of Pentium 4, the pipeline was increased further to 31 stages.
AMD’s 32 bit Athlon line can barely make it much above a clock frequency of 2 GHz, because of the short pipeline. In comparison, the Pentium 4 is almost ”light years” ahead.
Chapter 31. FPU’s and multimedia
The computer is constantly performing calculations, which can be divided into two groups.
The whole number calculations are probably the most important, certainly for normal PC use – using office programs and the like. But operations involving floating point numbers have taken on greater significance in recent years, as 3D games and sound, image and video editing have become more and more a part of everyday computing. Let’s have a brief look at this subject.
Floating point numbers
The CPU has to perform a lot of calculations on decimal (or real) numbers when the PC runs 3D games and other multimedia programs.
These decimal numbers are processed in the CPU by a special unit called an FPU (Floating Point Unit). In case you are wondering (as I did) about the name, floating point – here is an explanation: Real numbers (like the number π , pi) can have an infinite number of decimal places. In order to work with these, often very large, numbers, they are converted into a special format.
First the required level of precision is set. Since the numbers can have an infinite number of decimals, they have to be rounded. For example, one might choose to have five significant digits, as I have done in the examples below (inside the PC, one would probably choose to have many more significant digits).
Once the precision has been set, the numbers are converted as shown below (the decimal point floats):
Now the FPU can manage the numbers and process them using the arithmetic operators.
Normal form
|
Rewritten
|
In the FPU
|
1,257.45
|
0.12575 x 104
|
12575 +4
|
0.00696784
|
0.69678 x 10-2
|
69678 -2
|
FPU – the number cruncher
Floating point numbers are excessively difficult for the CPU’s standard processing unit (the ALU) to process. A huge number of bits are required in order to perform a precise calculation. Calculations involving whole numbers (integers) are much simpler and the result is correct, every time.
That is why an FPU is used – a special calculating unit which operates with floating point numbers of various bit lengths, depending on how much precision is needed. FP numbers can be up to 80 bits long, whereas normal whole numbers can “only” be up to 32 bits (permitting 4,294 billion different numbers). So the FPU is a number cruncher, which relieves the load on the ALU’s. You can experiment with large numbers yourself, for example, in a spreadsheet.
In Excel 2000, 21023 (the number 2, multiplied by itself 1023 times), is the biggest calculation I can perform. The result is slightly less than 9 followed by 307 zeroes.
Modern CPU’s have a built-in FPU (Floating Point Unit) which serves as a number cruncher. But it hasn’t always been like this.
For example, Intel’s 80386 processor didn’t have a built-in FPU calculating unit. All calculations were done using the processor’s ALU. But you could buy a separate FPU (an 80387), which was a chip which you mounted in a socket on the motherboard, beside the CPU. However, in the 80486 processor, the FPU was built-in, and it has been that way ever since.
3D graphics
Much of the development in CPU’s has been driven by 3D games. These formidable games (like Quake and others) place incredible demands on CPU’s in terms of computing power. When these programs draw people and landscapes which can change in 3-dimensional space, the shapes are constructed from tiny polygons (normally triangles or rectangles).
A character in a PC game might be built using 1500 such polygons. Each time the picture changes, these polygons have to be drawn again in a new position. That means that every corner (vortex) of every polygon has to be re-calculated.
In order to calculate the positions of the polygons, floating point numbers have to be used (integer calculations are not nearly accurate enough). These numbers are called single-precision floating points and are 32 bits long. There are also 64-bit numbers, called double-precision floating points, which can be used for even more demanding calculations.
When the shapes in a 3D landscape move, a so-called matrix multiplication has to be done to calculate the new vortexes. For just one shape, made up of, say, 1000 polygons, up to 84,000 multiplications have to be performed on pairs of 32-bit floating point numbers. And this has to happen for each new position the shape has to occupy. There might be 75 new positions per second. This is quite heavy computation, which the traditional PC is not very good at. The national treasury’s biggest spreadsheet is child’s play compared to a game like Quake, in terms of the computing power required.
The CPU can be left gasping for breath when it has to work with 3D movements across the screen. What can we do to help it? There are several options:
We have seen that clock frequencies are constantly increasing in the new generations of CPU. But the FPU’s themselves have also been greatly enhanced in the latest generations of CPU’s. The Athlon, especially, is far more powerfully equipped in this area compared to its predecessors.
The last method has also been shown to be very effective. CPU’s have simply been given new registers and newinstructions which programmers can use.
MMX instructions
The first initiative was called MMX (multimedia extension), and came out with the Pentium MMX processor in 1997. The processor had built-in “MMX instructions” and “MMX registers”.
The previous editions of the Pentium (like the other 32 bit processors) had two types of register: One for 32-bit integers, and one for 80-bit decimal numbers. With MMX we saw the introduction of a special 64-bit integer register which works in league with the new MMX instructions. The idea was (and is) that multimedia programs should exploit the MMX instructions. Programs have to be “written for” MMX, in order to utilise the new system.
MMX is an extension to the existing instruction set (IA32). There are 57 new instructions which MMX compatible processors understand, and which require new programs in order to be exploited.
Many programs were rewritten to work both with and without MMX (see Fig 96). Thus these programs could continue to run on older processors, without MMX, where they just ran slower.
MMX was a limited success. There is a weakness in the design in that programs either work with MMX, or with the FPU, and not both at the same time – as the two instruction sets share the same registers. But MMX laid the foundation for other multimedia extensions which have been much more effective.
3DNow!
In the summer of 1998, AMD introduced a collection of CPU instructions which improved 3D processing. These were 21 new SIMD (Single Instruction Multiple Data) instructions. The new instructions could process several chunks of data with one instruction. The new instructions were marketed under the name, 3DNow!. They particularly improved the processing of the 32-bit floating point numbers used so extensively in 3D games.
3DNow! was a big success. The instructions were quickly integrated into Windows, into various games (and other programs) and into hardware manufacturers’ driver programs.
SSE
After AMD’s success with 3DNow!, Intel had to come back with something else. Their answer, in January 1999, was SSE (Streaming SIMD Extensions), which are another way to improve 3D performance. SSE was introduced with the Pentium III.
In principle, SSE is significantly more powerful than 3DNow! The following changes were made in the CPU:
SSE also quickly became a success. Programs like Photoshop were released in new SSE optimised versions, and the results were convincing. Very processor-intensive programs involving sound, images and video, and in the whole area of multimedia, run much more smoothly when using SSE.
Since SSE was such a clear success, AMD took on board the technology. A large part of SSE was built into the AthlonXP and Duron processors. This was very good for software developers (and hence for us users), since all software can continue to be developed for one instruction set, common to both AMD and Intel.
SSE2 and SSE3
With the Pentium 4, SSE was extended to use even more powerful techniques. SSE2 contains 144 new instructions, including 128-bit SIMD integer operations and 128-bit SIMD double-precision floating-point operations.
SSE2 can reduce the number of instructions which have to be executed by the CPU in order to perform a certain task, and can thus increase the efficiency of the processor. Intel mentions video, speech recognition, image/photo processing, encryption and financial/scientific programs as the areas which will benefit greatly from SSE2. But as with MMX, 3DNow! and SSE, the programs have to be rewritten before the new instructions can be exploited.
SSE2 adopted by the competition, AMD, in the Athlon 64-processors. Here AMD even doubled up the number of SSE2 registers compared to the Pentium 4. Latest Intel has introduced 13 new instructions in SSE3, which Intel uses in the Prescott-version of Pentium 4.
We are now going to leave the discussion of instructions. I hope this examination has given you some insight into the CPU’s work of executing programs.
Chapter 32. Examples of CPU’s
In this chapter I will briefly describe the important CPU’s which have been on the market, starting from the PC’s early childhood and up until today.
One could argue that the obsolete and discontinued models no longer have any practical significance. This is true to some extent; but the old processors form part of the “family tree”, and there are still legacies from their architectures in our modern CPU’s, because the development has been evolutionary. Each new processor extended and built “on top of” an existing architecture.
There is therefore value (one way or another) in knowing about the development from one generation of CPU’s to the next. If nothing else, it may give us a feeling for what we can expect from the future.
16 bits – the 8086, 8088 and 80286
The first PC’s were 16-bit machines. This meant that they could basically only work with text. They were tied to DOS, and could normally only manage one program at a time.
But the original 8086 processor was still “too good” to be used in standard office PC’s. The Intel 8088 discount model was therefore introduced, in which the bus between the CPU and RAM was halved in width (to 8 bits), making production of the motherboard much cheaper. 8088 machines typically had 256 KB, 512 KB or 1 MB of RAM. But that was adequate for the programs at the time.
Protected mode paved the way for the change from DOS to Windows, which only came in the 1990’s.
32 bits – the 80386 and 486
The Intel 80386 was the first 32-bit CPU. The 386 has 32-bit long registers and a 32-bit data bus, both internally and externally. But for a traditional DOS based PC, it didn’t bring about any great revolution. A good 286 ran nearly as fast as the first 386’s – under DOS anyway, since it doesn’t exploit the 32-bit architecture.
The 80386SX became the most popular chip – a discount edition of the 386DX. The SX had a 16-bit external data bus (as opposed to the DX’s 32-bit bus), and that made it possible to build cheap PC’s.
The fourth generation
The fourth generation of Intel’s CPU’s was called the 80486. It featured a better implementation of the x86 instructions – which executed faster, in a more RISC-like manner. The 486 was also the first CPU with built-in L1 cache. The result was that the 486 worked roughly twice as fast as its predecessor – for the same clock frequency.
With the 80486 we gained a built-in FPU. Then Intel did a marketing trick of the type we would be better off without. In order to be able to market a cheap edition of the 486, they hit on the idea of disabling the FPU function in some of the chips. These were then sold under the name, 80486SX. It was ridiculous – the processors had a built-in FPU; it had just been switched off in order to be able to segment the market.
But the 486 was a good processor, and it had a long life under DOS, Windows 3.11 and Windows 95. New editions were released with higher clock frequencies, as they hit on the idea of doubling the internal clock frequency in relation to the external (see the discussion later in the guide). These double-clocked processors were given the name, 80486DX2.
A very popular model in this series had an external clock frequency of 33 MHz (in relation to RAM), while working at 66MHz internally. This principle (double-clocking) has been employed in one way or another in all later generations of CPU’s. AMD, IBM, Texas Instruments and Cyrix also produced a number of 80486 compatible CPU’s.
Pentium
In 1993 came the big change to a new architecture. Intel’s Pentium was the first fifth-generation CPU. As with the earlier jumps to the next generation, the first versions weren’t especially fast. This was particularly true of the very first Pentium 60 MHz, which ran on 5 volts. They got burning hot – people said you could fry an egg on them. But the Pentium quickly benefited from new process technology, and by using clock doubling, the clock frequencies soon skyrocketed.
Basically, the major innovation was a superscalar architecture. This meant that the Pentium could process several instructions at the same time (using several pipelines). At the same time, the RAM bus width was increased from 32 to 64 bits.
Throughout the 1990’s, AMD gained attention with its K5 and K6 processors, which were basically cheap (and fairly poor) copies of the Pentium. It wasn’t until the K6-2 (which included the very successful 3DNow! extensions), that AMD showed the signs of independence which have since led to excellent processors like the AthlonXP.
Figure 103. One of the earlier AMD processors. Today you’d hesitate to trust it to run a coffee machine…
In 1997, the Pentium MMX followed (with the model name P55), introducing the MMX instructions already mentioned. At the same time, the L1 cache was doubled and the clock frequency was raised.
Pentium II with new cache
After the Pentium came the Pentium II. But Intel had already launched the Pentium Pro in 1995, which was the first CPU in the 6th generation. The Pentium Pro was primarily used in servers, but its architecture was re-used in the popular Pentium II, Celeron and Pentium III models, during 1997-2001.
The Pentium II initially represented a technological step backwards. The Pentium Pro used an integrated L2 cache. That was very advanced at the time, but Intel chose to place the cache outside the actual Pentium II chip, to make production cheaper.
The Level 2 cache was placed beside the CPU on a circuit board, an SEC module (e.g. see Fig. 71). The module was installed in a long Slot 1 socket on the motherboard. Fig. 106 shows the module with a cooling element attached. The CPU is sitting in the middle (under the fan). The L2 cache is in two chips, one on each side of the processor.
The disadvantage of this system was that the L2 cache became markedly slower than it would have been if it was integrated into the CPU. The L2 cache typically ran at half the CPU’s clock frequency. AMD used the same system in their first Athlons. For these the socket was called, Slot A (see Fig. 107).
At some point, Intel decided to launch a discount edition of the Pentium II – the Celeron processor. In the early versions, the L2 cache was simply scrapped from the module. That led to quite poor performance, but provided an opportunity for overclocking.
Overclocking means pushing a CPU to work at a higher frequency than it is designed to work at. It was a very popular sport, especially early on, and the results were good.
One of the problems of overclocking a Pentium II was that the cache chips couldn’t keep up with the high speeds. Since these Celerons didn’t have any L2 cache, they could be seriously overclocked (with the right cooling).
Intel later decided to integrate the L2 cache into the processor. That happened in a new versions of the Celeron in 1998 and a new versions of the Pentium III in 1999. The socket design was also changed so that the processors could be mounted directly on the motherboard, in a socket called socket 370. Similarly, AMD introduced their socket A.
Pentium 4 – long in the pipe
The Pentium III was really just (yet) another edition of the Pentium II, which again was a new version of the Pentium Pro. All three processors built upon the same core architecture (Intel P6).
It wasn’t until the Pentium 4 came along that we got a completely new processor from Intel. The core (P7) had a completely different design:
All of these factors are described elsewhere in the guide. The important thing to understand, is that the Pentium 4 represents a completely new processor architecture.
Evolution of the Pentium 4
As was mentioned earlier, the older P6 architecture was released back in 1995. Up to 2002, the Pentium III processors were sold alongside the Pentium 4. That means, in practise, that Intel’s sixth CPU generation has lasted 7 years.
Similarly, we may expect this seventh generation Pentium 4 to dominate the market for a number of years. The processors may still be called Pentium 4, but it comes in al lot varietes.
A mayor modification comes with the version using 0.65 micron process technology. It will open for higher clock frequencies, but there will also be a number of other improvements.
Hyper-Threading Technology is a very exciting structure, which can be briefly outlined as follows: In order to exploit the powerful pipeline in the Pentium 4, it has been permitted to process two threads at the same time. Threads are series of software instructions. Normal processors can only process one thread at a time.
In servers, where several processors are installed in the same motherboard (MP systems), several threads can be processed at the same time. However, this requires that the programs be set up to exploit the MP system, as discussed earlier.
The new thing is that a single Pentium 4 logically can function as if there physically were two processors in the pc. The processor core (with its long pipelines) is simply so powerful that it can, in many cases, act as two processors. It’s a bit like one person being able to carry on two independent telephone conversations at the same time.
Hyper-Threading works very well in Intel’s Prescott-versions of Pentium 4. You gain performance when you operate more than one task at the time. If you have two programs working simultaneously, both putting heavy pressure on the CPU, you will benefit from this technology. But you need a MP-compatible operating system (like Windows XP Professional) to benefit from it.
The next step in this evolution is the production of dual-core processors. AMD produces Opteron chips which hold two processors in one chip. Intel is working on dual core versions of the Pentium 4 (with the codename ”Smithfield”). These chips will find use in servers and high performance pc’s. A dual core Pentium 4 with Hyper-Threading enabled will in fact operate as a virtual quad-core processor.
Intel also produces EE-versions of the Pentium 4. EE is for Extreme Edition, and these processors are extremely speedy versions carrying 2 MB of L2 cache.
In late 2004 Intel changed the socket design of the Pentium 4. The new processors have no ”pins”; they connect directly to the socket using little contacts in the processor surface.
Athlon
The last processor I will discuss is the popular Athlon and Athlon 64 processor series (or K7 and K8).
It was a big effort on the part of the relatively small manufacturer, AMD, when they challenged the giant Intel with a complete new processor design.
The first models were released in 1999, at a time when Intel was the completely dominant supplier of PC processors. AMD set their sights high – they wanted to make a better processor than the Pentium II, and yet cheaper at the same time. There was a fierce battle between AMD and Intel between 1999 and 2001, and one would have to say that AMD was the victor. They certainly took a large part of the market from Intel.
The original 1999 Athlon was very powerfully equipped with pipelines and computing units:
All in all, the Athlon was in a class above the Pentium II and III in those years. Since Athlon processors were sold at competitive prices, they were incredibly successful. They also launched the Duron line of processors, as the counterpart to Intel’s Celeron, and were just as successful with it.
 |
Figure 113.
Athlon was a huge success for AMD. During 2001-2002, the Athlon XP was in strong competition with the Pentium 4. |
Athlon XP versus Pentium 4
The Athlon processor came in various versions. It started as a Slot A module (see Fig. 107 on page 42). It was then moved to Socket A, when the L2 cache was integrated.
In 2001, a new Athlon XP version was released, which included improvements like a new Hardware Auto Data Prefetch Unit and a bigger Translation Look-aside Buffer. The Athlon XP was much less advanced than the Pentium 4 but quite superior at clock frequencies less than 2000 MHz. A 1667 MHz version of AthlonXP was sold as 2000+. This indicates, that the processor as a minimum performs like a 2000 MHz Pentium 4.
Later we saw Athlons in other versions. The latest was based on a new kernel called ”Barton”. It was introduced in 2003 with a L2-cachen of 512 KB. AMD tried to sell the 2166 MHz version under the brand 3000+. It did not work. A Pentium 4 running at 3000 MHz had no problems outperforming the Athlon.
Opteron/ Athlon64
AMD’s 8th generation CPU was released in 2003. It is based on a completely new core called Hammer.
A new series of 64-bits processors is called Athlon 64, Athlon 64 FX and Opteron. These CPU’s has a new design in two areas:
Moving the memory controller into the CPU is a great innovation. It gives a much more efficient communication between CPU and RAM (which has to be ECC DDR SDRAM – 72 bit modules with error correction).)
Every time the CPU has to fetch data from normal RAM, it has to first send a request to the chipset’s controller. It has to then wait for the controller to fetch the desired data – and that can take a long time, resulting in wasted clock ticks and reduced CPU efficiency. By building the memory controller directly into the CPU, this waste is reduced. The CPU is given much more direct access to RAM. And that should reduce latency time and increase the effective bandwidth.
The Athlon 64 processors are designed for 64 bits applications. This should be more powerful than the existing 32 bit software. We will probably see plenty of new 64 bit software in the future, since Intel is releasing 64 bit processors compatible with the Athlon 64 series.
Overall the Athlon 64 is an updated Athlon-processor with integrated north bridge and 64 bits instructions. Other news are:
A complete line of chips
AMD expects to use the K8 kernel in all types of processors: |
The Opteron is the most expensive and advanced version to be used in multi-processor servers. The models are called 200, 400 and 800, and they use 2, 4 or 8 CPUs on the same motherboard – without use of a north bridge.
All processors share a common memory of up to 64 GB. Each Opteron has three HyperTransport I/O channels, which each can move 6,4 GB/secund.
|
 |
The Athlon FX is a Opteron to be used in single processor configurations, high-end pc’s and workstations. There is dual RAM interface, but only one channel of Hyper Transport Link.
|
 |
This is the discount version with reduced performance and lower prices. Only 64 bit RAM interface and smaller L2-cache.
|
Figure 115. Three versions of the latest AMD processor.
Historical overview
I will close off this review with a graphical summary of a number of different CPU’s from the last 25 years. The division into generations is not always crystal clear, but I have tried to present things in a straightforward and reasonably accurate way:
Figure 116. There are scores of different processors. A selection of them is shown here, divided into generations.
But what is the most powerful CPU in the world? IBM’s Power4 must be a strong contender. It is a monster made up of 8 integrated 64-bit processor cores. It has to be installed in a 5,200 pin socket, uses 500 watts of power (there are 680 million transistors), and connects to a 32 MB L3 cache, which it controls itself. Good night to Pentium.
Chapter 33. Choosing a CPU
If you happen to need to choose a CPU for your new PC, what should you choose? Let me give you a bit of food for thought.
Processor
|
Euro
| ||
INTEL Celeron 2.66 GHZ/533 256KB
|
70,00
| ||
INTEL P4 520 2.8 GHZ/800 1 MB
|
130,00
| ||
INTEL P4 530 3.0 GHZ/800 1 MB
|
145,00
| ||
INTEL P4 540 3.2 GHZ/800 1 MB
|
175,00
| ||
INTEL P4 550 3.2 GHZ/800 1 MB
|
220,00
| ||
INTEL P4 560 3.2 GHZ/800 1 MB
|
330,00
| ||
AMD Sempron 3100+ (1,8 GHZ)
|
105,00
| ||
AMD ATHLON 64 3000+ (2,0 GHz)
|
209,00
| ||
AMD ATHLON 64 3400+ (2,4 GHz)
|
227,00
| ||
AMD ATHLON 64 FX-53 (2,4 GHz)
|
670,00
| ||
How long does a CPU last?
The individual components have different lifetimes. The way development has gone up until the present, CPU’s and motherboards have been the components that have become obsolete the most quickly. CPU’s and motherboards also go together – you normally change them both at the same time.
You have by now read all of my review of new processor technology; new and faster models are constantly being developed. The question is, then, how important is it to have the latest technology? You have to decide that for yourself. But if you know that your PC has to last for many years, you probably should go for the fastest CPU on the market.
For the rest of us, who regularly upgrade and replace our PC’s insides, it is important to find the most economic processor. There is usually a price jump in the processor series, such that the very latest models are disproportionately expensive.
By the time you read this, prices will have fallen in relation to those shown in Fig. 117. There will no doubt also be significantly faster CPU’s to choose between. But the trend will most likely be the same: The latest models are a lot more expensive than the other ones. You have to find the model that gives the most power in proportion to the price.
Also, the amount of RAM is just as important as the speed of the processor. RAM prices fluctuate unbelievably, in just a year the price can double or halve. So it’s a good idea to buy your RAM when the prices are low.
CPU-intensive operations
Back in the 1990’s it was quite important to get the latest and fastest CPU, because CPU’s were not fast enough for things like image processing. For example, if you try to work with fairly large images in Photoshop, on a PC with a 233 MHz processor, you will probably quickly decide to give up the project.
But whether you have 2400 or 3200 MHz – that’s not as critical, especially if you have enough RAM and are working with normal tasks. A processor running at 3200 MHz is roughly 33% faster than a 2400 MHz model, but it doesn’t always make that much difference to your daily work.
Here are some tasks, which might require more CPU power:
Video (including DVD) contains huge amounts of data. The CPU and RAM therefore have to work very hard when you edit video footage. At the time of writing, it is legal to copy DVD films for personal use, but that may change. Legal or not – it’s certainly possible. The actual ripping can take 10-20 minutes, during which the CPU slowly chews through the over 4 GB of data there are on a DVD. A 5 GHz CPU would obviously be able to reduce the time taken considerably.
Finally, speech recognition software is considered to be very CPU-intensive. This is probably only going to be a problem in the distant future. Some people imagine future versions of Windows and Office programs will have built-in speech recognition, which will place quite new demands on CPU’s. However, it is far from certain that speech recognition will ever be introduced into PC’s. There appear to be big problems in getting it to work well.
Chapter 34. The CPU’s immediate surroundings
In the second part of this guide, we dug down into the inner workings of the CPU. We well let it rest in peace now, and concentrate on the processor’s immediate surroundings. That is, the RAM and the chipset – or more precisely, the north bridge.
In the first section of the guide I introduced the chipset, including the north bridge (see, for example, Fig. 46, which connects the CPU to the PC’s memory — the RAM.
The most important data path on the motherboard runs between the CPU and the RAM. Data is constantly pumped back and forth between the two, and this bus therefore often comes under focus when new generations of CPU’s, chipset’s and motherboards are released.
The RAM sends and receives data on a bus, and this work involves a clock frequency. This means that all RAM has aspeed, just like a CPU does. Unfortunately RAM is much slower than the CPU, and the buses on the motherboard have to make allowance for this fact.
The XT architecture
In the original PC design (the IBM XT), the CPU, RAM and I/O devices (which we will come to later) were connected on one and the same bus, and everything ran synchronously (at a common speed). The CPU decided which clock frequency the other devices had to work at:
The problem with this system was that the three devices were “locked to each other”; they were forced to work at the lowest common clock frequency. It was a natural architecture in the first PC’s, where the speed was very slow.
The first division of the bus
In 1987, Compaq hit on the idea of separating the system bus from the I/O bus, so that the two buses could work at different clock frequencies. By letting the CPU and RAM work on their own bus, independent of the I/O devices, their speeds could be increased.
In Fig. 119, the CPU and RAM are connected to a common bus, called the system bus, where in reality the CPU’s clock frequency determines the working speed. Thus the RAM has the same speed as the CPU; for example, 12, 16 or 25 MHz.
The I/O devices (graphics card, hard disk, etc.) were separated from the system bus and placed on a separate low speed bus. This was because they couldn’t keep up with the clock frequencies of the new CPU versions.
The connection between the two buses is managed by a controller, which functions as a “bridge” between the two paths. This was the forerunner of the multibus architecture which all motherboards use today.
Clock doubling
With the introduction of the 80486, the CPU clock frequency could be increased so much that the RAM could no longer keep up. Intel therefore began to use clock doubling in the 80486 processor.
The RAM available at the time couldn’t keep up with the 66 MHz speed at which an 80486 could work. The solution was to give the CPU two working speeds.
Inside the processor, the clock frequency of the system bus is multiplied by a factor of 2, doubling the working speed.
But this system places heavy demands on the RAM, because when the CPU internally processes twice as much data, it of course has to be “fed” more often. The problem is, that the RAM only works half as fast as the CPU.
For precisely this reason, the 486 was given a built-in L1 cache, to reduce the imbalance between the slow RAM and the fast processor. The cache doesn’t improve the bandwidth (the RAM doesn’t work any faster), but it ensures greater efficiency in the transfer of data to the CPU, so that it gets the right data supplied at the right time.
Clock doubling made it possible for Intel to develop processors with higher and higher clock frequencies. At the time the Pentium was introduced, new RAM modules became available, and the system bus was increased to 66 MHz. In the case of the Pentium II and III, the system bus was increased to 100 and 133 MHz, with the internal clock frequency set to a multiple of these.
Overclocking
The Pentium II was subjected to a lot of overclocking. It was found that many of Intel’s CPU’s could be clocked at a higher factor than they were designed for.
If you had a 233 MHz Pentium II, you could set up the motherboard to, for example, run at 4.5 x 66 MHz, so that the processor ran at 300 MHz. I tried it myself for a while, it worked well. At a factor of 5 it didn’t work, but at factor of 4.5 it functioned superbly.
CPU
|
System bus
|
Clock
factor |
Internal clock
frequency |
Pentium
|
66 MHz
|
1.5
|
100 MHz
|
Pentium MMX
|
66 MHz
|
2.5
|
166 MHz
|
Pentium II
|
66 MHz
|
4.5
|
300 MHz
|
Pentium II
|
100 MHz
|
6
|
600 MHz
|
Celeron
|
100 MHz
|
8
|
800 MHz
|
Pentium III
|
133 MHz
|
9
|
1200 MHz
|
AthlonXP
|
133 MHz x 2
|
13
|
1733 MHz
|
AthlonXP+
|
166 MHz x 2
|
13
|
2167 MHz
|
Pentium 4
|
100 MHz x 4
|
22
|
2200 MHz
|
Pentium 4
|
133 MHz x 4
|
23
|
3066 MHz
|
Pentium 4
|
200 MHz x 4
|
18
|
3600 MHz
|
Figure 122. The CPU’s internal clock frequency is locked to the system bus frequency.
Overclocking the system bus
Another method of overclocking was to turn up the system bus clock frequency. In the early versions of the Pentium II, the system bus was at 66 MHz, which suited the type of RAM used at that time.
You could increase the bus speed, for example to 68 or 75 MHz, depending on how fast your RAM was. This type of tuning makes both the CPU and RAM faster, since it is the actual system clock speed which is increased.
The disadvantage is that the system clock in these motherboard architectures also controls the I/O bus, which runs synchronously with the system bus. PCI bus devices (which we will come to in a later chapter) cannot handle being overclocked very much; otherwise faults can occur, for example in reading from the hard disk.
Overclocking typically requires a higher voltage for the CPU, and most motherboards can be set up to supply this:
Many still use the same kind of overclocking on the Athlon XP and Pentium 4. The system clock has to be able to be adjusted in increments, which it can on many motherboards.
Example using the Pentium 4
A Pentium 4 processor is designed for a system clock of 200 MHz. If you can have a 3200 MHz model with a 200 MHz system bus, it can theoretically be clocked up to 4000 MHz by turning up the system clock. However, the processor needs a very powerful cooling system to operate at the increased frequencies:
System clock
|
CPU clock
|
200 MHz
|
3200 MHz
|
230 MHz
|
3700 MHz
|
250 MHz
|
4000 MHz
|
Figure 125. Overclocking a Pentium 4 processor.
The manufacturers, Intel and AMD, don’t like people overclocking their CPU’s. They have sometimes attempted to prevent this by building a lock into the processors, so that the processor can only work at a specific clock frequency. In other cases the CPU’s can be overclocked. In any case, you shouldn’t expect your warranty to apply if you play around with overclocking.
Chapter 35. Different types of RAM
RAM works in synch with the system bus, as I described in the previous chapter. But what is RAM actually? RAM is a very central component in a PC, for without RAM there can be no data processing. RAM is simply the storage area where all software is loaded and works from.
Silicon storage area
RAM is made in electronic chips made of so-called semiconductor material, just like processors and many other types of chips.
In RAM, transistors make up the individual storage cells which can each “remember” an amount of data, for example, 1 or 4 bits – as long as the PC is switched on.
Normal RAM is dynamic (called DRAM), and requires constant electronic recharging to preserve its data contents. Without power, all RAM cells are cleared. RAM is very closely linked to the CPU, and it is very important to both haveenough RAM, and to have fast RAM. If both conditions are not met, the RAM will be a bottleneck which will slow down the PC. What follows is an introduction to RAM, as it is used in modern PC’s. After this I will discuss the various types I more detail.
Several types
At the time of writing, there are several types of RAM, which are quite different. This means that they normally cannot be used on the same motherboard – they are not compatible.
However, some motherboards can have sockets for two types of RAM. You typically see this during periods where there is a change taking place from one type of RAM to another. Such motherboards are really designed for the new type, but are made “backwards compatible”, by making room for RAM modules of the old type.
The RAM types on the market at the moment are:
RAM
type |
Pins
|
Width
|
Usage
|
SD RAM
|
168
|
64 bit
|
Older and slower type. No use.
|
Rambus RAM
|
184
|
16 bit
|
Advanced RAM. Only used for very few Pentium 4’s with certain Intel chipsets.
|
DDR RAM
|
184
|
64 bit
|
A faster version of SD RAM.
Used both for Athlon and Pentium 4’s. 2,5 Volt. |
DDR2
RAM |
240
|
64 bit
|
New version of DDR RAM with higher clock frequencies. 1,8 Volt.
|
In any case, there is a lot of development taking place in DDR. A number of new RAM products will be released within the next few years. The modules are packaged differently, so they cannot be mixed. The notches in the sides are different as the he bottom edges of the modules are.
SDRAM is an old and proven type, which is used in the majority of existing PC’s. DDR RAM is a refinement of SDRAM, which is in reality double clocked. Rambus RAM is an advanced technology which in principle is superior to DDR RAM in many ways. However, Rambus has had a difficult birth. The technology has been patented by Rambus Inc., which has been involved in many legal suits. A number of important manufacturers (such as VIA) have opted out of Rambus, and only develop products which use DDR RAM. With the new DDR2 standard, there is no obvious need for Rambus RAM.
Notes on the physical RAM
RAM stands for Random Access Memory. Physically, RAM consists of small electronic chips which are mounted in modules (small printed circuit boards). The modules are installed in the PC’s motherboard using sockets — there are typically 2, 3 or 4 of these. On this motherboard there are only two, and that’s a bit on the low side of what is reasonable.
Each RAM module is a rectangular printed circuit board which fits into the sockets on the motherboard:
On a module there are typically 8 RAM chips which are soldered in place. There can also be 16 if it is a double-sided module. Below is a single RAM chip:
 | Figure 130. A single RAM chip, a 256 megabit circuit. |
On the bottom edge of the module you can see the copper coated tracks which make electrical contact (the edge connector). Note also the profile of the module; this makes it only possible to install it one way round and in the right socket.
Module or chip size
All RAM modules have a particular data width, which has to match the motherboard, chipset, and ultimately the CPU. Modules using the two most common RAM types, SD and DDR RAM, are 64 bits wide.
The modules are built using chips which each contain a number of megabits. And since each byte needs 8 bits, more than one chip is needed to make a module. Look at the RAM chip in Fig. 130. You can see the text ”64MX4”:
The text in Fig. 132 indicates that the chip contains 64 x 4 mega bits of data, which is the same as 256 megabits. If we want to do some calculations, each chip contains 1024 x 1024 x 64 = 67,108,864 cells, which can each hold 4 bits of data. That gives 268,435,456 bits in total, which (when divided by 8) equals 33,554,432 bytes = 32,768 KB = 32 MB.
So a 64MX4 circuit contains 32 MB, and is a standard product. This type of chip is used by many different manufacturers to make RAM modules. Modules are sold primarily in four common sizes, from 64 to 512 MB:
Number of chips per module
|
Module size
|
2 (single-sided)
|
2 x 256 Mbit = 64 Mbyte
|
4 (single-sided)
|
4 x 256 Mbit = 128 Mbyte
|
8 (single-sided)
|
8x 256 Mbit = 256 Mbyte
|
16 (double-sided)
|
16 x 256 Mbit = 512 Mbyte
|
Figure 133. The module size is determined by what RAM chips are used.
RAM speeds
For each type of RAM, there are modules of various sizes. But there are also modules with various speeds. The faster the RAM chips are, the more expensive the modules.
Name
|
Type
|
PC700
|
2x 356 MHz Rambus RAM
|
PC800
|
2x 400 MHz Rambus RAM
|
PC1066
|
2 x 533 MHz Rambus RAM
|
DDR266 el. PC2100
|
2x 133 MHz DDR RAM
|
DDR333 el. PC2700
|
2x 166 MHz DDR RAM
|
DDR400 el. PC3200
|
2x 200 MHz DDR RAM
|
DDR2-400
|
400 MHz DDR2 RAM
|
DDR2-533
|
533 MHz DDR2 RAM
|
DDR2-667
|
667 MHz DDR2 RAM
|
Figure 134. The speed is measured in megahertz, but it is not possible to compare directly between the three types of RAM shown in the table. The names shown are those which are being used on the market at the time of writing, but they may change.
RAM technologies
Let’s look a little more closely at the technology which is used in the various types of RAM.
In the old days
Back in the 1980’s, DRAM was used. This was dynamic RAM, which was relatively slow. It was replaced by FPM (Fast Page Mode) RAM which was also dynamic, only a bit faster.
Originally, loose RAM chips were installed directly in large banks on the motherboard. Later people started combining the chips in modules. These came in widths of 8 bits (with 30 pins) and 32 bits (with 72 pins). The 32-bit modules were suited to the system bus for the 80486 processor, which was also 32 bits wide.
FPM RAM could not run any faster than 66 MHz, but that was fine for the system bus clock frequency in the original Pentium processors.
After FPM came EDO RAM (Extended Data Out). EDO is a bit faster than FPM because the data paths to and from the RAM cells have been optimised. The gain was a 3-5 % improvement in bandwidth. The clock frequency could be increased to 75 MHz, but basically, EDO is not very different to FPM RAM.
When Intel launched the Pentium processor, there was a change to using the 64 bit wide RAM modules (with 168 pins, as in Fig. 127, which are still used for SDRAM today.
SDRAM
The big qualitative shift came in around 1997, when SDRAM (Synchronous DRAM) began to break in. This is a completely new technology, which of course required new chipsets. SDRAM, in contrast to the earlier types of RAM, operates synchronously with the system bus.
Data can (in burst mode) be fetched on every clock pulse. Thus the module can operate fully synchronised with (at the same beat as) the bus – without so-called wait states (inactive clock pulses). Because they are linked synchronously to the system bus, SDRAM modules can run at much higher clock frequencies.
The 100 MHz SDRAM (PC100) quickly became popular, and with new processors and chipsets, the speed was brought up to 133 MHz (PC133).
Another innovation in SDRAM is the small EEPROM chip called the Serial Presence Detect chip, which is mounted on the modules. It is a very small chip containing data on the modules speed, etc.
DDR RAM
It is expensive to produce fast RAM chips. So someone hit on a smart trick in 1999-2000, which in one blow made normal RAM twice as fast. That was the beginning of DDR RAM (Double Data Rate). See the module in Fig. 131.
In DDR RAM, the clock signal is used twice. Data is transferred both when the signal rises, and when it falls. This makes it possible to perform twice as many operations per clock pulse, compared to earlier RAM types:
Timings
DDR RAM exist in many versions, with different the clock frequencies and timings. The timing indicates how many clock cycles there are wasted, when the motherboard waits for the memory to deliver the requested data.
With smaller numbers, we have better timings and the CPU having fewer idle clock cycles. You may find memory modules of the same clock frequency but with different timings. The better timing, the more expensive the RAM module is.
Ordinary pc users need not to speculate in special RAM with fast timing; this is primary sold to gamers and over-clockers, who tries to achieve the maximum performance from their motherboards.
Module
|
Clock frequency
|
Timing
|
PC2100
|
2 x 133 MHz
|
2-2-2
|
PC 2700
|
2 x 166 MHz
|
2-2-2
2-3-3 |
PC 3200
|
2 x 200 MHz
|
2-3-2
2-3-3 |
PC 3700
|
2 x 233 MHz
|
3-4-4
|
PC 4000
|
2 x 250 MHz
|
3-4-4
|
PC 4400
|
2 x 275 MHz
|
3-4-4
|
Note that different timing means that the gain in terms of increased bandwidth doesn’t quite match the clock speed. It is a bit less.
Next generation RAM
In the beginning the problem with DDR RAM, was that the RAM modules were poorly standardized. A module might work with a particular motherboard, but not with another. But this – which was typical for a new technological standard – is not a big problem anymore. Intel was initially against DDR RAM. They claimed that Rambus was a much better design, and that they wouldn’t use DDR RAM. But consumers wanted DDR RAM, which Intel’s competitors were able to deliver, and in the end even Intel had to give in. At the end of 2001, the i845 chipset was released, which uses DDR RAM for the Pentium 4, and later we had the i865 and i875 chip sets, which use dual channel DDR RAM.
The next generation of RAM is the DDR2, which is a new and better standardized version of DDR using less power. The DDR2 modules operates at higher clock speeds due to better design with higher signal integrity and a more advanced internal data bus. The first chip sets to use DDR2 was Intel’s i915 and i925. Later DDR4 is expected with clock frequencies of up to 1,6 GHz!
Rambus RAM
Rambus Inc., as already mentioned, has developed a completely new type of RAM technology. Rambus uses a completely different type of chip, which are mounted in intelligent modules that can operate at very high clock frequencies. Here is a brief summary of the system:
Rambus RAM thus has a completely new and different design. The modules are only 16 bits wide. Less data is transferred per clock pulse, but the clock frequencies are much higher. The actual Rambus modules (also called RIMM modules) look a bit like the normal SDRAM modules as we know them. They have 184 pins, but as mentioned, the ships are protected by a heat-conducting casing:
As the advanced Rambus modules are quite costly to produce, the technology is on its way out of the market.
Advice on RAM
RAM can be a tricky thing to work out. In this chapter I will give a couple of tips to anyone having to choose between the various RAM products.
Bandwidth
Of course you want to choose the best and fastest RAM. It’s just not that easy to work out what type of RAM is the fastest in any given situation.
We can start by looking at the theoretical maximum bandwidth for the various systems. This is easy to calculate bymultiplying the clock frequency by the bus width. This gives:
Module type
|
Max.
transfer |
SD RAM, PC100
|
800 MB/sec
|
SD RAM, PC133
|
1064 MB/sec
|
Rambus, PC800
|
1600 MB/sec
|
Rambus, Dual PC800
|
3200 MB/sec
|
DDR 266 (PC2100)
|
2128 MB/sec
|
DDR 333 (PC2700)
|
2664 MB/sec
|
DDR 400 (PC3200)
|
3200 MB/sec
|
DUAL DDR PC3200
|
6400 MB/sec
|
DUAL DDR2-400
|
8600 MB/sec
|
DUAL DDR2-533
|
10600 MB/sec
|
Figure 140. The highest possible bandwidth (peak bandwidth) for the various types of RAM.
However, RAM also has to match the motherboard, chipset and the CPU system bus. You can try experimenting with overclocking, where you intentionally increase the system bus clock frequency. That will mean you need faster RAM than what is normally used in a given motherboard. However, normally, we simply have to stick to the type of RAM currently recommended for the chosen motherboard and CPU.
RAM quality
The type of RAM is one thing; the RAM quality is something else. There are enormous differences in RAM prices, and there are also differences in quality. And since it is important to have a lot of RAM, and it is generally expensive, you have to shop around.
One of the advantages of buying a clone PC (whether you build it yourself or buy it complete) is that you can use standard RAM. The brand name suppliers (like IBM and Compaq) use their own RAM, which can be several times more expensive than the standard product. The reason for this is that the RAM modules have to meet very specific specifications. That means that out a particular production run, only 20% may be “good enough”, and that makes them expensive.
Over the years I have experimented with many types of RAM in many combinations. In my experience, for desktop PC’s (not servers), you can use standard RAM without problems. But follow these precautions:
How much RAM?
RAM has a very big impact on a PC’s capacity. So if you have to choose between the fastest CPU, or more RAM, I would definitely recommend that you go for the RAM. Some will choose the fastest CPU, with the expectation of buying extra RAM later, “when the price falls again”. You can also go that way, but ideally, you should get enough RAM from the beginning. But how much is that?
If you still use Windows 98, then 256 MB is enough. The system can’t normally make use of any more, so more would be a waste. For the much better Windows 2000 operating system, you should ideally have at least 512 MB RAM; it runs fine with this, but of course 1024 MB or more is better. The same goes for Windows XP:
128 MB
|
256 MB
|
512 MB
|
1024
MB | |
Windows 98
|
**
|
***
|
Waste
|
Waste
|
Windows 2000
|
*
|
**
|
***
|
****
|
Windows XP
|
*
|
***
|
****
|
Figure 141. Recommended amount of PC RAM, which has to be matched to the operating system.
The advantage of having enough RAM is that you avoid swapping. When Windows doesn’t have any more free RAM, it begins to artificially increase the amount of RAM using a swap file. The swap file is stored on the hard disk, and leads to a much slower performance than if there was sufficient RAM in the PC.
RAM addressing
Over the years there have been many myths, such as ”Windows 98 can’t use more than 128 MB of RAM”, etc. The issue is RAM addressing.
Below are the three components which each have an upper limit to how much RAM they can address (access):
Windows 95/98 has always been able to access lots of RAM, at least in theory. The fact that the memory management is so poor that it is often meaningless to use more than 256 MB, is something else. Windows NT/2000 and XP can manage several gigabytes of RAM, so there are no limits at the moment.
In Windows XP, you have to press Control+Alt+Delete in order to select the Job list. A dialog box will then be displayed with two tabs, Processes and Performance, which provide information on RAM usage:
Under the Processes tab, you can see how much RAM each program is using at the moment. In my case, the image browser, FotoAlbum is using 73 MB, Photoshop, 51 MB, etc., as shown in Fig. 143.
Modern motherboards for desktop use can normally address in the region of 1½-3 GB RAM, and that is more than adequate for most people. Server motherboards with special chipsets can address much more.
Standard motherboards normally have a limited number of RAM sockets. If, for example, there are only three, you cannot use any more than three RAM modules (e.g. 3 x 256 MB or 3 x 512 MB).
CPU’s have also always had an upper limit to how much RAM they can address:
Processor
|
Address bus
width (bits) |
Maximum
System RAM |
8088, 8086
|
20
|
1 MB
|
80286, 80386SX
|
24
|
16 MB
|
80386DX, 80486, Pentium, Pentium MMX, K5, K6 etc.
|
32
|
4 GB
|
Pentium Pro, Pentium II, III
Pentium 4 |
36
|
64 GB
|
Figure 144. The width of the CPU’s address bus determines the maximum amount of RAM that can be used.
Let me conclude this examination with a quote. It’s about RAM quantity:
”640K ought to be enough for anybody.”Bill Gates, 1981.
hapter 39. From ISA to PCI Express
From about 1984 on, every PC had a standard bus which was used for I/O tasks. That was the ISA (Industry Standard Architecture) bus.
Right up until about 1999 there were still ISA slots in most PC’s. In the later years, however, they were only kept for compatibility, so that plug-in cards of the old ISA type could be re-used. This was particularly the case for sound cards from SoundBlaster; they worked quite well on the ISA bus, and many games were programmed to directly exploit this type of hardware. It therefore took many years to get away from the ISA bus, but we have managed to now.
History of the ISA bus
The ISA bus is thus the I/O bus which survived the longest. Here is some information about it:
ISA was an improvement to IBM’s original XT bus (which was only 8 bits wide) IBM used the protected name ”AT Bus”, but in everyday conversation it was called the ISA bus.
|
The ISA bus was 16 bits wide, and ran at a maximum clock frequency of 8 MHz.
|
The bus has a theoretical bandwidth of about 8 MB per second. However in practise it never exceeds about 1-2 MB/sec. – partly because it takes 2-3 of the processor’s clock pulses to move a packet (16 bits) of data.
|
Figure 166. The ISA bus is not used much today, but it had enormous significance in the years up until the middle of the 1990’s.
The ISA bus had two ”faces” in the old PC architecture:
Sluggish performance
One of the reasons the ISA bus was slow was that it only had 16 data channels. The 486 processor, once it was introduced, worked with 32 bits each clock pulse. When it sent data to the ISA bus, these 32-bit packets (dwords ordoublewords) had to be split into two 16-bit packets (two words), which were sent one at a time, and this slowed down the flow of data.
Bus
|
Time per
packet |
Amount of data per
packet |
ISA
|
375 ns
|
16 bits
|
PCI
|
30 ns
|
32 bits
|
The ISA bus was not ”intelligent” either, since it was in principle the CPU which controlled all the work the bus was doing. This meant the CPU could only begin a new task when the transfer was complete. You may perhaps have experienced yourself, that when your PC works with the floppy disk drive – the rest of the PC virtually grinds to a halt. That’s the ISA bus’s fault, and it therefore only happens on older PC’s.
These small delays are called wait states. If an ISA adapter cannot keep up with the data it is receiving, it sends wait states to the CPU. These are signals to the CPU telling it to do nothing. A wait state is a wasted clock pulse – the CPU skips over a clock pulse, without doing anything. Thus a slow ISA adapter could choke any PC.
Another problem was that the ISA bus often played up when you were installing an expansion card (e.g. a sound card). Many of the problems were associated with the handling of IRQ’s and DMA channels (I will explain these terms later), which often had to be done ”by hand” with the old ISA bus.
Every device takes up one particular IRQ, and possibly a DMA channel, and conflicts often arose with other devices. It was a big relief when Intel, in the late 1990’s, finally dropped the ISA bus and replaced it with the smart USB bus.
Figure 168. ISA based Sound Blaster sound card.
The MCA, EISA and VL buses
The ISA bus was too slow, and the solution was to develop new standards for I/O devices. In 1987-88, two new I/O buses were put forward. First, IBM brought out their technologically advanced MCA bus. But since it was patented, a number of other companies pooled together to create the equivalent EISA bus.But neither MCA or EISA had a big impact on the clone market. We were stuck with the ISA bus up until 1993, when the VL bus finally became reasonably widespread. It was a genuine local bus, which means it worked synchronously with the system bus. The VL bus was very primitive; it was really just an extension of the system bus.
The VL bus never managed to have a big impact, because almost at the same time, the robust and efficient PCI bus broke through. The various I/O buses are summarised below:
Bus
|
Description
|
PC-XT
from 1981 |
Synchronous 8-bit bus which followed the CPU clock frequency of 4.77 or 6 MHz.
Band 170: 4-6 MB/sec. |
ISA (PC-AT)
from 1984 |
Simple, cheap I/O bus.
Synchronous with the CPU. Band width: 8 MB/sec. |
MCA
from 1987 |
Advanced I/O bus from IBM (patented). Asynchronous, 32-bit, at 10 MHz.
Band width: 40 MB/sec. |
EISA From 1988
|
Simple, high-speed I/O bus.
32-bit, synchronised with the CPU’s clock frequency: 33, 40, 50 MHz. Band width: up to 160 MB/sec. |
PCI
from 1993 |
Advanced, general, high-speed I/O bus. 32-bit, asynchronous, at 33 MHz.
Band width: 133 MB/sec. |
USB and Firewire, from 1998
|
Serial buses for external equipment.
|
PCI Express
from 2004 |
A serial bus for I/O cards with very high speed. Replaces PCI and AGP.
500 MB/sec. per. Channel. |
The PCI bus
PCI stands for Peripheral Component Interconnect. The bus is an Intel product which is used in all PC’s today, and also in other computers, as the PCI bus is processor independent. It can be used with all 32-bit and 64-bit processors, and is therefore found in many different computer architectures.
Figure 170. PCI bus adapter.
At the same time, the bus is compatible with the ISA bus to a certain extent, since PCI devices can react to ISA bus signals, create the same IRQ’s etc. One consequence of this was that Sound Blaster compatible sound cards could be developed, which was very important in the middle of the 1990’s. In optimal conditions, the PCI bus sends one packet of data (32 bits) each clock pulse. The PCI bus therefore has a maximum bandwidth of 132 MB per second, as shown below:
Clock
frequency: |
33 MHz
|
Bus width:
|
32 bits
|
Bandwidth:
|
32 bits x 33,333,333 clock pulses/second =
4 bytes x 33,333,333 clock pulses/second = 132 MB per second |
There is also a more powerful versions of the PCI standard, which provides greater bandwidth, but most motherboards still use the original version. The PCI bus has a buffer which operates between the CPU and the peripheral devices (a kind of cache RAM). This allows the CPU to deliver its data to the buffer, and then perform other tasks. The bus looks after the rest of the delivery itself at its own pace. Alternatively, PCI adapters can also deliver data to the buffer, whether or not the CPU has time to process it. The data just stands in a queue and waits until there is room on the system bus, which then relays it to the CPU.
As a result of all this, the peripheral PCI devices operate asynchronously – at their own pace – in relation to the CPU. Thus the PCI bus (in contrast to the VL bus) is not a local bus from a technical perspective.
Figure 172. The PCI bus is being refined by a Special Interest Group. You can follow their progress yourself on the Net (www.pcisig.com).
Plug and Play
The Plug and Play standard is part of the PCI specification. It means that all PCI adapter cards are self-configuring. The specification for Plug and Play was developed by Microsoft and Intel, among others, and the ideas was (as the name suggests) to provide a system where one can simply install an adapter and it will work. It’s not quite this simple in practise; a software driver has to normally be installed before an adapter will work. But the actual cooperation between adapter, motherboard and operating system – happens automatically. During startup, communication takes place between the PC’s startup programs, the PCI controller and each PCI device (adapter).The adapter has to be able to inform the I/O bus which I/O addresses and IRQ’s it can operate with. And it has to be able to configure itself to use the resources allocated to it by the I/O bus. When the exercise is successful, the adapter is configured automatically, and is ready to be used by the operating system.
All the components involved (adapter, motherboard and Windows) have to be Plug and Play compatible for the system to work.
Figure 173. Schematic overview of Plug and Play.
ESCD
In connection with Plug and Play, it is necessary also to discuss the Extended System Configuration Data (ESCD) system. This is a small data area which is stored in the motherboard’s CMOS storage.The ESCD store is used to save adapter configuration information. This means the motherboard doesn’t have to go through the whole plug and play operation at each startup – information about the PC’s configuration can be read from the CMOS storage.
The ESCD also allows the user to manually allocate an IRQ etc., for a particular adapter. This can be done using the motherboard’s setup program. Read more about the CMOS on page 90.
Figure 174. Using the CMOS setup program, the user can directly allocate resources for PCI adapters.
See the devices during startup
All I/O devices have small, built-in registers (in ROM circuits), which contain various information. The registers can, for example, describe the nature of the device (e.g. a network card, video card or SCSI controller, etc.) and the manufacturer. You can see this information for yourself during PC startup, when the devices are configured:
Figure 175. The PCI devices ”identify themselves” during startup as they are configured.
PCI Express development
In
This new I/O bus will be extremely scalable, as it works with a large number of channels (X1, X2, X16 etc.), each of which has a bandwidth of about 250 MB/second in both directions, simultaneously.
The standard plans for the use of plug-in cards and devices in various categories, with varying bandwidths and power consumption. A 16X video card, for example, will totally be able to pull about 8 GB/sec.
PCI Express is based on a serial architecture, making it possible to develop smaller and cheaper devices with many fewer pins. The new I/O bus will initially co-exist with the PCI interface, as we se it in the motherboards with Intel i900-series chip sets. But the goal is that PCI Express should replace both PCI and AGP.
Figure 176. The two black slots are for PCI Express cards. To the left a 16X card for the graphics controller and to the right a smaller 1X slot. Inb
Chapter 40. I/O buses using IRQ’s
I/O buses are designed to move data. Data is transferred from one I/O device to another, and from the I/O devices to the CPU and RAM. Let’s delve a little deeper into the architecture which makes this possible.
At the physical level, the PCI bus consists of a number of parallel printed tracks on the motherboard. These tracks are used for:
Hardware interrupts
When you install a plug-in card in a slot, the card gets connected to the I/O bus. That means that data can run to and from the card. To manage the traffic on the I/O buses, a system is used, called IRQ. This stands for Interrupt Request.
Interrupts are basically one of the foundational principles of the PC architecture. There are two types: Software interrupts are used to call a large number of BIOS routines. Hardware interrupts are what we are now going to discuss, because these are what the I/O devices use.
An interrupt signal is a doorbell used by the various PCI adapters and other devices. By setting an IRQ signal, they can ask to “have the floor” – to be allowed to interrupt the CPU in the middle of its work. The device places a voltage across one of the conductors on the bus – it sets an IRQ. When the CPU registers the signal, it knows that the device wants to fetch or deliver data, or has finished doing so.
The IRQ signals are managed by a PIC (Programmable Interrupt Controller), which is a controller device on the motherboard.
In the original PC design, the PIC was a ”loose” controller chip (called Intel 8259). In modern motherboards the chipset’s south bridge contains an equivalent, 8259-compatible, PIC function.
A practical example
The advantage of IRQ’s is that the CPU can keep working on other tasks while an adapter “digests” the data it has to look after. When the adapter has finished its work, it notifies the CPU using a new IRQ signal – it rings the doorbell again.
Let’s look at the keyboard as an example. Every time you press a key, an IRQ is sent from the keyboard controller to the CPU. First, the keyboard sends its data as a series of individual bits along the keyboard cable. The bits are received on the motherboard by the keyboard controller. On modern PC’s this function is included in the Super I/O controller, but it used be on a separate 8042 chip. When the keyboard controller has collected one byte – that is one character – it sends an IRQ signal to the PIC (the IRQ controller).
The signal requests permission from the CPU to send the character on. The PIC notifies the keyboard controller when the way is clear to the CPU, and then the byte is moved onto the I/O bus. At the physical level, an IRQ is a printed track on the bus. The printed track connects to all the PCI slots on the motherboard, so no matter which slot the adapter is installed in it has contact with the IRQ system.
8 or 15 IRQ lines
In the original PC architecture, an 8259 Programmable Interrupt Controller was used on the motherboard. It could handle 8 IRQ lines. This was later extended to two controllers with a total of 15 lines (one of the lines is used to connect the two PIC’s). That means there are 15 IRQ’s available to I/O devices. They are used for several tasks.
Certain system devices, such as the FPU (the number cruncher discussed earlier, and the system clock, each lay claim to one IRQ. Five of the IRQ’s are reserved for internal system devices like these. In Fig. 179 these are, for example, IRQ numbers 0, 8 and 13.
The remaining IRQ’s are available for I/O devices. You can also see in Fig. 179 that a number of IRQ’s are free. E.g. numbers 5, 7 and 10.
Each of the IRQ’s is a physical printed track that runs throughout the whole bus and hence the whole motherboard. The IRQ’s have different priorities, so that the CPU knows which IRQ should be given preference, if two signals are set at the same time.
You can use the Windows Device Manager (or System Information) to see the way IRQ’s are distributed on your PC, as shown in Fig. 179. They should hopefully match.
Shared IRQ’s – a typical PC solution
One of the big innovations in the PCI bus is that it allows shared IRQ’s. Two adapters can actually share an IRQ. In my PC there are no less than six devices sharing IRQ 11, and it works faultlessly.
The invention of ”shared IRQ’s” is a good example of the evolutionary development of the PC architecture. The basic fault lies with the thin and undersized IRQ system; there are only 15 “doorbells” available in the system, and that is far too few.
It would be logical to extend the system to, for example, 256 doorbells. But that is not possible for compatibility reasons. The IRQ system is located at a very deep level in the PC architecture, and it would require complete reprogramming of both the CPU instructions and the operating systems if one changed it. And the PC would no longer be able to run, for example, old DOS programs.
In order to maintain compatibility, a ”work-around” solution is typically chosen. A stopgap solution you could say – but one which works. A doorman is employed at each doorbell. He checks who is ringing the doorbell – which device is using the IRQ. And voila, using shared IRQ’s, the system works again!
How it was in the old days …
Before the PCI bus came along we were stuck with the ISA bus, which was very limited by the small number of IRQ’s. It didn’t take much before you were short of free IRQ’s if you needed several adapters in your PC. Sound cards used to especially play up. Sound cards are quite complex pieces of equipment, incorporating several functions. The old ISA based Sound Blaster cards usually claimed two IRQ’s and nothing less than two DMA channels as well. A card like that could be very difficult to install.
An ISA network card, might be configured by the manufacturer to work with IRQ 9, 10, 11 or 12, for example. One of the values (e.g. IRQ 11) was chosen as the standard factory setting (as the default value). When the customer installed the new network card, it would try, at startup, to go on the bus as IRQ 11. If there was no other device using IRQ 11 already, the card would probably work fine. But if IRQ 11 had been claimed by another card, there would be problems – the two devices had a conflict. Often the PC wouldn’t even start, and the air was thick with panic.
The solution was, for example, to change an IRQ jumper on the physical network card, and then try again. We are fortunately completely spared from that kind of mess with the newer PC’s. The PCI bus checks itself which adapters are using shared IRQ’s, and the system functions quite automatically and problem free.
View the shared IRQ’s
Look a bit more closely at Fig. 179. The first thing to note is that it relates to an older motherboard, which also has an ISA bus. That is apparent by the fact that (ISA) is written in front of a number of the IRQ’s. Don’t be too concerned about that, because the ISA bus is not actually used for anything – nor are the IDE controllers, although you could get that impression from IRQ 14 and 15.
The following devices have been listed as located on the PCI bus, and they all use IRQ 11.
These devices are:
Device
|
Description
|
Creative SB Audigy
|
Sound card
|
D-Link Ethernet
|
Network controller (network card)
|
HPT 370
|
A RAID controller, built into the motherboard.
|
IEEE1394
|
FireWire controller, built into the sound card.
|
Radeon VE
|
Video card (which is on the AGP bus).
|
VIA USB
|
USB host controller, built into the south bridge.
|
Figure 180. Six logical devices which share the same IRQ.
DMA and bus mastering
DMA stands for Direct Memory Access, and is a system on the motherboard which permits an adapter to transfer its data to RAM – without drawing on the PC’s data processing power. It’s actually the CPU which controls every event on the bus. With DMA, this intelligence has been put out in the DMA controller on the motherboard.
This special controller chip (Intel 8237, often integrated into the modern south bridge) is allowed to move data to and from RAM, via the I/O bus. And this happens without the CPU being burdened with the work.
The motherboard has a number of DMA channels, each assigned a number. They are used by the ISA devices, which can each lay claim to one of the DMA channels. The floppy drive, for example, uses DMA:
There are no direct DMA channels on the PCI bus. Instead, bus mastering is used. It is a very similar system, where special controller functions permit adapters to take control of the bus. The adapters can then deliver their data directly to RAM, in a way which burdens the CPU as little as possible. It doesn’t have to monitor the transaction – the bus master looks after that.
The goal is that the PC can multitask – that is, handle several tasks at the same time. The hard disk can deliver data to RAM in a steady stream, while the CPU does other work at the same time. The bus mastering system works well with ATA devices, which work closely with RAM.
Though in this area, the SCSI controller is much more developed than the ATA controller. In practise, SCSI disks can operate almost independently of the CPU. SCSI interfaces are therefore still used to control hard disks in high-end servers and workstations.
Memory-mapped I/O
All devices, adapters, ports, etc. each have their own address. It is also called an I/O port number. The I/O address is necessary for the CPU (or RAM) to be able to fetch and send data to and from the device. The way this takes place inside the PC is called memory mapping of I/O devices.
I’m not exactly sure how much practical benefit is derived from understanding this system. But it is part of the whole story, so I’ll give you a quick overview. When you want to send data to your network card, it takes place through one or more I/O ports. These ports are located in RAM – that’s actually the whole idea.
Thus when you want to send data to your network card, you send it to a particular area in the RAM. And the network card is ready to fetch its data from the same place, as soon as it gets the signal from the interrupt controller.
The PC can address (access) every byte in the RAM storage. And this addressing is exploited in the I/O ports. Every adapter is allocated a specific RAM address. That is, a small portion of RAM is linked to the I/O device. From then on, all data exchange to and from the device passes through this ”mailbox”.
All I/O devices have their own ”mailbox number” – a port address. Since the PC is fundamentally a 16-bit computer, there are a total of 2 to the 16 (216 = 65,536) possible port addresses. They are specified using hexadecimal numbers, from 0000h up to FFFFh. Here are some examples of I/O addresses, as seen using the Windows Device Manager.
The table of I/O addresses takes up the ”bottom” 64 KB of the PC’s working storage ( from 0000h to FFFFh). The I/O addresses fall inside that special ”first megabyte of RAM” – which you might like to read about in the guide “Do it yourself DOS”. The individual I/O addresses can have varying lengths of up to 64 bytes.
We can see here that the system of I/O addresses was designed right back in around 1980, and is still being used. It is fortunately very rare that one, as a user, has to set up port addresses. Certain network cards support user-defined I/O addresses, but you would have to be very unlucky to encounter a conflict in this area.
Chapter 41. Check your adapters
I have now described adapters and their bus connections in a number of more theoretical sections.
Let’s look at the subject a little more practically. I will use my own PC as an example, to show which adapters are installed and what I can learn from them.
Look in the cabinet
If you are going to follow my examination using your own PC, start by looking in the cabinet and seeing what adapters (plug-in cards) are actually installed. I have three cards installed:
The three cards are:
I can see this from the back of the cabinet. There I can see the card’s back plates and connectors, and they look like this:
A closer look at a sound card
I will now take a closer look at one of my adapters. I have chosen the middle card, which is a sound card, a Sound Blaster Audigy. It is a bit unusual in that it has a built-in FireWire port. That is, the card has several functions; it operates as a sound card with many facilities. And it also functions as an IEEE-1394 (FireWire) host controller. This is what the card physically looks like:
Since the card has several functions, it appears in several places in the list of system devices. I can find it under sound devices, where there are two devices (Creative Gameport and Creative SB Audigy) which are components of this adapter. And further down I can see the FireWire controller (IEEE 1394):
If I double-click on the device ”Creative SB Audigy”, I see the following information displayed:
I can read that the actual sound functions are located on PCI bus 0 (there can be several PCI buses on the same motherboard). The adapter is installed as device 8. The sound component is function number 0.
If I double-click on the device ”Creative Gameport”, I can see that the game port is function number 1 on this card.
Finally, I will look at the FireWire controller. It has function number 2 on device 8 (which is the SB card):
Figure 190. The FireWire controller is the last function on this sound card.
Check your own cards
In the section above I have shown how you can use the Windows Device Manager to investigate the PC’s I/O system. You can do this in all versions of Windows. However, Windows 98 doesn’t provide the Location information (as at the bottom of Fig. 190. Both Windows 2000 and XP provide this.
In all versions of Windows, you can open System Properties by using the shortcut key, Windows+Pause, and then clicking your way in to the Device manager.
Examine your PC’s I/O devices yourself now as follows:
1. First find out what adapters you have in your PC. Note which sockets (slots) the cards are installed in, and check the connectors on the back plate so that you are sure of their function.
2. Note the information displayed on the screen when you start the PC (as in Fig. 175, on page 68). You can stop the screen scrolling using the P key to give you time to note the information.
3. Then open the Windows Device Manager and find the devices corresponding to your plug-in cards.
4. See what IRQ’s they use, and note where they are located on the PCI bus, if you can find this.
5. Compare your observations on IRQ allocation with the messages you see on the screen during PC startup. Are these consistent? Is it the same adapters and IRQ’s you can see in both places?
6. Then use the Device Manager to find an overview of the IRQ allocation. Compare this with Fig. 179. Which IRQ’s are shared? Which internal system devices can you see in your list?
7. Which DMA channels are being used in your PC? Compare this with Fig. 181.
8. Finally, investigate your hard disk and USB controllers. What can you find out about them?
If you spend some time doing this exercise I guarantee you will gain a better grasp of this part of the PC architecture!
Chapter 42. I/O and The south bridge
We have now looked at the various I/O buses, and the chipset’s south bridge plays the central role in the transfer of data on these buses. But, as mentioned before, the south bridge is assisted by a small Super I/O controller. Let me describe it briefly.
Functions of the south bridge
The south bridge is a chip on the motherboard. If we want to look at one of the latest models, we could take the south bridge from Intel’s 915 chipset, which is designed for motherboards with Pentium 4 processors.
A peek at the chip’s specifications reveals that it contains the following components and functions:
Component
|
Description
|
DMI
|
Direct Media Interface is the connection to the memory with a bandwidth of max 2 GB/sec.
|
PCI Express
|
Hi-speed bus for I/O adapters
|
PCI ports
|
Standard I/O bus.
|
Serial ATA
|
Controller for up to four SATA hard disks
|
Matrix Storage
|
Advanced Host Controller Interface for RAID 0 and 1 on the same drives. Including support for Native Command Queuing and hot plug drive swaps.
|
Ultra ATA/100
|
Controller for PATA devices like hard disks, DVD- and CD-drives.
|
USB ports
|
Hi-speed USB 2.0 ports.
|
7.1 channel audio
|
Option for integrated sound device with surround, Dolby Digital and DTS.
|
AC97 modem
|
Integrated modem.
|
Ethernet
|
Integrated 10/100 Mbs network
controller. |
Figure 192. Selected functions in a modern south bridge.
But a number of traditional controllers for the floppy disk drive etc. are missing. These can be placed in the Super I/O controller.
Super I/O
The so-called Super I/O controller is found on all motherboards. It is a helper chip, which looks after a number of the less demanding controller functions for the south bridge.
The tasks of the Super I/O controller are quite well-defined: it is therefore fine to use a mass-produced, standard chip, which can be used on virtually any motherboard. This helps keep prices down, and these Super I/O controllers come from companies like Winbond and ITE.
The super I/O controller is connected to the south bridge using a special low-speed bus, and this architecture is called LPC (Low Pin Count). The chip is a 128-pin chip containing these components:
Controller
|
Description
|
FDC
|
82077-compatible floppy disk controller
|
UART
|
Serial port, 16550-compatible controller, including IrDA (infrared)
|
LPT
|
Parallel printer port
|
Game
|
For a joystick
|
KBD
|
8042-compatible keyboard controller
|
PS/2
|
Mouse port
|
LED
|
Controls the small LED’s in the cabinet
|
Fan
|
Controls the fan
|
Figure 194. Functions which the Super I/O chip typically takes care of.
You will find many different layouts of the motherboard. The south bridge may be connected to other controller chips. This could be:
It is up to the individual motherboard manufacturers to decide how they will use the chipset. The south bridge offers loads of facilities which can be implemented if desired.
For example, some south bridges have built-in primitive sound devices (based on the AC-97 standard). This uses the CPU to process sound. On some motherboards this functionality will be put to use, while other manufacturers will choose to integrate a “real” sound chip from, for example, Creative.
In any case, some users will choose to install a separate sound card with even more functionality – regardless of what sound features the motherboard offers.
The serial and parallel ports
The serial and parallel ports are included in the I/O system, and their controller is located in the Super I/O controller.
The PC is equipped with at least one (usually two) asynchronous serial ports. These are the male connectors on the back of the PC, which have either 9 or 25 pins, of which often only 3-4 are used for serial transmission.
The parallel port is also called the printer port, because that is what it is normally used for. The printer connector on the back of the PC is a 25-pin female connector.
The ports are also called COM1, COM2 and LPT. These are so-called logical device names, which the PC startup program automatically allocates to these devices during startup, just as A:, C:, CON, PRN and KBD are logical names.
Today the serial ports and serial devices are used much less than they used to be. This is especially due to the USB bus, which can connect equivalent devices. But if you use, for example, a USB based modem, it will behave just as if it was a normal serial device. Below an ISDN adapter is installed, which is connected via USB. It creates two virtual COM ports which can be seen using the Device Manager. In this way the Internet dialup program can use the USB device in exactly the same way as if it was connected to a (physical) COM port:
Figure 198. The COM3 and COM9 ports are actually a USB device.
Asynchronous transmission
The serial ports work using asynchronous transmission, which it might be interesting to know a little bit about.
Asynchronous transmission means that data can be transferred at irregular intervals, as you might already be familiar with from using a modem. The transmission only starts when the receiver is ready to receive. And the receiver can use unlimited time to ”digest” the data. The opposite principle is synchronous transmission, where a shared clock controls the pace.
The irregularity means that you have to be able to work out when to send data, and when a portion of data has been sent completely. This is achieved using a protocol, which defines the packet sizes, etc., which the sender and receiver have to agree on.
When the sender has nothing to say, a stream of 1’s is sent. At the start of a transmission, a 0 is sent. After this start bit, the data is sent in portions of 5, 6, 7 or 8 bits. Then follows 0, 1 or 2 so-called parity bits, which are used to perform a simple check on the transfer, and the packet is closed with 1 or 2 stop bits. The most common standard is 8 data bits, no parity bit and 1 stop bit. This system is often called 8/N/1.
The necessary ”packaging” of data into portions for serial transmission takes place in the UART chip, which is part of the Super I/O controller.
UART stands for Universal Asynchronous Receiver/Transmitter. The UART chip converts the data stream between the parallel I/O bus and the serial connection. Bytes from the I/O bus have to be “chopped up” into series of bits and “framed” with stop bits, etc., and this takes place in the UART.
Figure 200. The UART controller repackages data in order to be able to perform a serial transfer.
Chapter 43. SCSI, USB and Firewire
In this chapter I need to discuss three I/O buses. They are very different, but they still belong together.
As I mentioned, the three buses are very different, but they also overlap with each other. For example, you can buy CD burners with all three types of interface.
SCSI
SCSI (Small Computer System Interface) is an advanced controller technology, which is especially used in high-end PC’s. These can be network servers or just powerful workstations, for which there are a number of different SCSI standards. The SCSI bus can transfer up to 160 MB/second, which is more than the PCI bus can deliver.
A SCSI system is built around a central controller, called the host adapter, which is almost a tiny computer in its own right. The adapter can be quite expensive if, for example, it has to be used with very fast hard disks. However there are simpler SCSI adapters, for example, those sold with SCSI based scanners.
 |
Figure 202.
A small SCSI controller. Note the wide cable. |
The best known manufacturer of SCSI adapters is Adaptec. It used to also be quite common for motherboards to have built-in SCSI controller – often of high quality.
A host adapter can control a number of SCSI devices, which are connected in a long series (a chain). Every device is allocated an identification number, and a terminator has to be put in at both ends of the SCSI chain. This is done, for example, using a jumper on one of the devices.
The SCSI controller has its own startup routine in which it identifies the devices which are connected. The startup procedure can be followed in the screen:
SCSI is intelligent
The big advantage of SCSI is the intelligent protocol which manages the devices and ensures optimal data transfer. Each device requests, for example, data from the host adapter, which then does all the work of acquiring this data. While each SCSI device is working, the controller has time to do other tasks.
The SCSI controller actually manages an entire small network of I/O devices, and thus relieves the CPU of the burden of all the associated work. SCSI therefore works well in multitasking environments such as web servers. These can have scores of SCSI disks organised in RAID chains.
Today, SCSI is used primarily for tape units (streaming tape) or hard disks in servers in large network servers (e.g. used by Internet service providers).
SCSI disks have a greater transfer capacity than standard ATA drives, and are more robust and generally better quality. SCSI used to be the only option if you wanted a big hard disk. But in recent years, ATA drive specifications have greatly improved, and today they are comparable with SCSI disks.
One consequence of the technological advances has been that the SCSI standard has lost a great deal of its significance. For scanners, the USB and FireWire I/O buses are used instead. These are much easier to configure, and have the advantage of small connectors and thin cables.
Figur 205. SCSI hard disks anno 2004.
RAID
RAID stands for Redundant Array of Inexpensive Disks. It is a disk technology that connects together a serious of standard hard disks to form an advanced, error correcting system, which is used in servers.
The system is virtually an extension of the SCSI standard, and was first used in 1987. Since then, ATA-based RAID systems have been developed which use the much cheaper ATA or SATA disks in an equivalent configuration (see the discussion later in the guide). The trick is, that you can spread your data over several disks. With a RAID chain of hard disks, you gain two advantages:
There are several RAID categories. A RAID controller has to be used, which is a special SCSI adapter. Here is a brief description of some of the standards:
Level
|
Technique
|
RAID 0
|
Two or more disks are connected together, and the files are split between them (striping). The goal is purely greater speed, as the controller can read from/write to several disks at the same time. There is no extra security.
|
RAID 1
|
Two hard disks are used. Purely provides increased security, as the data is written twice – first normally, and then to the mirror disk. If the first disk goes down, the second is immediately ready to replace it.
|
RAID 0/1
|
Uses four disks and combines the two techniques above.
|
RAID 3
|
Spreads the data over several disks and stores parity data on one of them.
|
RAID 5
|
Improves both performance and security. Uses at least three, usually four disks. Is considered to be the best principle.
|
USB
USB stands for Universal Serial Bus and is an I/O standard originally developed by seven companies – Compaq, Digital, IBM, Intel, Microsoft, NEC and Northern Telecom (see the USB Implementers Forum at www.usb.org).
USB is a cheap serial I/O bus with an open specification. This means that anyone can produce USB products, without having to pay licences to anyone.
USB has been the biggest and most welcome innovation in PC design seen for many years. It is an expansion bus which allows a vast amount of PC equipment to be connected. It’s suddenly possible to connect loads of different gadgets to the PC – and using just one type of connector! And USB devices can also be used both with Macintosh computers and PC’s – yet another advantage.
USB has been advertised since 1994, and for many years it was called the Useless Serial Bus. But starting in 1999, production finally surged forward, and there are now thousands of different USB gadgets.
USB unifies all the different connections for keyboard, mouse, scanner, joystick, digital camera, and perhaps printer, onto a shared bus – connected using a common connector type.
USB – the technology
From a technical viewpoint, the following can be said about USB:
There has to be a USB host controller in the PC in order to be able to connect the devices. This controller can be bought separately, as an adapter, but most motherboards have one built into the chipset’s south bridge. There are typically two or four USB connectors on the motherboard, but you can have many more USB devices than this if you connect an extra hub (e.g. integrated in a screen, as in Fig. 209.
A flexible bus
I am personally very grateful for USB. I find use for the following devices:
USB has thus made the serial ports (COM1 and COM2) redundant, and we can be very happy about that. The technology has also opened the door for the development of a number of new cheap and fun products.
Figure 209. This screen has a built-in USB hub in its base. That means that a further four USB devices can be connected to the screen, which is itself connected to the PC’s USB connector.
IEEE 1394 – FireWire
Another, more SCSI type, interface is called IEE 1394. It doesn’t look a lot like SCSI, as we know it, but the standard is an extension of the SCSI standard. IEEE 1394 (FireWire in everyday language) is a high-speed serial bus which has a maximum transfer rate of 400 Mbit per second.
Figure 210. A FireWire cable
Some computers are born with FireWire ports being integrated on the motherboard. On other PC’s, you can install a cheap little adapter; then you can have direct access to your digital DV video camera. IEEE 1394 connections are “hot”, i.e. you can connect and disconnect devices without having to restart your PC, just as for USB.
A summary
I have described three expansion buses in this chapter which, from a technological perspective, are very similar. For many years, SCSI has been a ”luxury bus” which made it possible to use a number of more sophisticated devices with a standard PC. But as I mentioned, the significance of SCSI is declining.From the beginning, USB was planned to particularly replace the PC’s serial COM ports. This has been very successful, and USB has become an indispensable element of the modern PC architecture.
At the time of writing, USB 2.0 is a completely new standard, but there is no doubt that it will be a big success, due to its good bandwidth and backward compatibility. As I mentioned, FireWire is used particularly on Macintosh computers and for DV cameras.
All digital cameras (as far as I know) have a FireWire port, which makes it very easy to download video footage for further processing on the PC. Windows XP is setup for this, as I described in my guide, ”Do it yourself Windows XP”.
Figure 211. In the middle of the picture you can see the small DV connecter on this digital video recorder.
For external disks (hard disks and CD/DVD drives), both USB version 2.0 and FireWire can be used. Maxtor, for example, supplies large, cheap, external hard disks using both interfaces.
Controller
|
Bandwidth
|
USB 1.1
|
1.2 MB/sec.
|
FireWire
|
40 MB/sec.
|
USB 2.0
|
40 MB/sec.
|
SCSI
|
Up to 160 MB/sec.
|
Chapter 44. Hard disks, ATA and SATA
I am now finally going to describe the ATA interface, which has been mentioned several times earlier in the guide. The ATA interface is used for hard disks (as in Fig. 20, and the motherboard’s ATA controller is built into the chipset’s south bridge, as shown in Fig. 195.
We have also seen, that ATA devices use bus mastering to exchange data directly with RAM. But what does this interface actually consist of? And why do new standards for hard disks keep coming out? We are going to look at that now.
History of the hard disk
It is critical that we have a place to save our programs and data when the PC is switched off. Otherwise it is useless. Twenty years ago, diskettes were used, but their capacity is very limited.
Right back in 1957, IBM introduced the first “fixed disk storage”. It was a big thing with 50 disks that were 24 inches in diameter. This very early hard disk had a capacity of 5 MB – a huge storage space at the time, which cost $35,000 a year to lease. One of IBM’s models was called the 3030, and in the weapons-conscious USA , this led to the hard disk being given the nickname, Winchester disk (a Winchester 3030 was a popular rifle) – a nickname that was also used in Europe for many years.
The first computer with a hard disk was IBM’s RAMAC, which was used during the 1960 Olympics to calculate sports results. A bit later, in 1962, removable disk packs were developed – a forerunner of the floppy disk. In 1964, the CRC algorithm was introduced. It provided greater security by checking and comparing data before and after it was written to the disk. In 1971, the first 8-inch diskettes came onto the market.
But it wasn’t until the middle of the 1980’s that people began to use hard disks in more standard PC’s, and since then development has surged ahead. The capacity of a standard hard disk has actually become a thousand times greater in the period 1990-2000.
The standard user’s need for disk space (e.g. for digital photos, video and music) has grown in step with this, so that 120-250 GB of disk space or more is normal in many PC’s – a figure which will double over the next few years.
Hard disks are constantly being developed which have greater capacity and speed (the two go together, as we shall see), and there is therefore a constant need for new types of hard disk controllers. The companies leading the development are Maxtor, Western Digital, IBM/Hitachi and Seagate.
The physical disk
Hard disks consist of one or more magnetic plates mounted in a metal box. The standard size (as in Fig. 213) is about 10 x 14.5 x 2.5 cm, and such a device can contain hundreds of gigabytes of data. Inside the box, a number of glass or metal plates whir around at, for example, 5400 or 7200 revolutions per minute – these being the two most common speeds.
The read/write heads hover over the magnetic plates, and can transfer data at a tremendous speed:
The actual read/write head is a tiny electromagnet. The magnet ends in a C-shaped head, the shape of which ensures that it virtually hovers above the magnetic plate. Under the read/write head are the disk tracks. These are thin rings packed with magnetic particles. These magnetic particles can be arranged in patterns of bits, which are translated into 0’s and 1’s by the electronics of the hard disk:
When the disk moves under the read/write head, it can either read the existing data or write new data to the disk:
The read/write heads are the most expensive part of the hard disk. When the disk is switched off, the heads are parked in a special area, so that they will not be damaged during transport. In Fig. 216, the cover has been removed from a hard disk, and you can see the uppermost arm with its read/write head.
Tracks and sectors
The individual files are written across a number of disk sectors (at least one), and this task is handled by the file system.
The file system is part of the operating system, which the disk has to formatted with. In Windows 98, the FAT32 file system is used. In Windows 2000/XP, you can also use NTFS. They are different systems for organising files and folder structures on the hard disk. You can read more about the file system in my guide, ”Do it yourself DOS”.
Hard disk development
New hard disk models are constantly being developed, and for each new generation, the capacity becomes greater. This is possible due to new read/write heads and magnetic plates which are more dense. When the magnetic density is increased, hard disks can be produced which have greater capacity for the same number of plates.
Another consequence of higher density is that the disks become faster, since they can transfer more data per rotation. There are simply more bits hidden in each track.
All hard disks have a certain amount of cache installed as 2 or 8 MB of fast RAM, which functions as a buffer. The cache helps ensure that the data gathered by the mechanics of the disk is optimally exploited.
The new and faster hard disks are always followed by new types of interface, since the controller principles have to be upgraded as well in order to handle the large amounts of data. At the time of writing, the fastest ATA interface is called ATA/133, but it is about to be replaced with Serial ATA (see Fig. 221).
The hard disk’s interface
The hard disk is managed by a controller built into the actual unit. This controller works together with a similar controller linked to the PC’s I/O bus (on the motherboard). I showed this setup in Fig. 20, in order to explain the concept of “interface”.
The interface’s job is to move data between the hard disk sectors and the I/O bus as fast as possible. It consists of:
In the ”old days”, interfaces such as ST-506 and ESDI were used. The ATA (AT Attachment) interfaces are based on the IDE standard (Integrated Drive Electronics). The names, IDE and ATA are “owned” by Western Digital, but are used anyway in everyday language.
Enhanced IDE
The IDE standard wasn’t especially fast, and couldn’t handle hard disks bigger than 528 MB. So the ATA standard came out in the mid-1990’s, and is still used today for cheap, high-performance, mass-produced hard disks. ATA is an enhanced edition of IDE, where the interface was moved from the ISA bus to the high-speed PCI bus. In principle, ATA (or parallel ATA) can be used for a number of different devices. The most common are:
ATA was developed as a cheap, all-round interface, designed for the different types of drives.
Host controller with two channels
The ATA interface can be seen as a bus, which is managed by a host controller. Up to four devices can be connected per host controller, and the devices connect directly to the motherboard.
The slightly unusual thing about the ATA interface is that there are two channels, which can each have two devices connected. They are called the primary and secondary channels. If two devices are connected to one channel, they have to be configured as one master and one slave device:
These four channels are standard on today’s motherboards using parallel ATA. Motherboards typically have connectors for two ATA cables, which can each connect two devices (master and slave).
These rectangular, male ATA connectors are placed in a fairly accessible location, and are used to connect the ribbon cables which fit hard disks and CD/DVD drives.
Transfer speeds and protocols
There are many ATA versions. The protocol has been changed over the years, but on the whole, the products arebackward compatible.
This means that you can readily connect an old CD-ROM drive which uses the PIO 3 protocol, for example, to a modern motherboard with an ATA/133 controller. The drive just won’t be any quicker as a result. The shift from parallel ATA/133 to Serial ATA is more profound. Here we use a different type of controller and new cables.
The various protocols have different transfer speeds, as shown in the table below.
Max. theoretical transfer rate
| |
PIO 3
|
13.3 MB/second
|
PIO 4
|
16.6 MB/second
|
Ultra DMA (ATA/33)
|
33 MB/second
|
ATA/66
|
66 MB/second
|
ATA/100
|
100 MB/second
|
ATA/133
|
133 MB/second
|
SATA
|
150 MB/second
|
The transfer speeds listed apply to the interface. Few hard disks can deliver more than 80 MB/second, but even so, it’s still good to have the fastest possible interface. If two hard disks are used on the same controller, or if disks with a large cache are used, there can be a need for big bandwidth for short periods.
With the ATA/66 standard, a new type of ATA cable was introduced. Hard disk cables normally have 40 conductors, but in the new version this is extended to 80, as each wire is balanced by a ground connection. This reduces electrical noise and allows for greater bandwidth.
Parallel ATA setup
If you build your own PC or upgrade it using a new hard disk or CD/DVD drive, it is important that you know the limitations of the parallel ATA system.
Modern motherboards can automatically recognize ATA devices. This means that, in principle, you can install your drive and start the PC, and it should work. You can follow the startup program while it “installs” the drive, as shown in Fig. 223, where two hard disks and CD burner are installed.
In the first four lines, the controller auto detects the four channels for connected devices. It then ”mounts” (configures) the two Maxtor hard disks on the primary channel, and finally the HP burner on the secondary channel. You can read this in the lines below:
Each ATA device has a small area containing jumpers which are used to set whether it is the master or slave device. If the startup is to proceed as painlessly as in Fig. 225, the jumpers have to set correctly on all devices, and of course the cables have to correctly connected.
Multitasking and protocol limitations
But this is not the case if two disks are connected to the same ATA channel. They cannot multitask. Either the master is working, or the slave is working, but not both at the same time. It is therefore best to install two hard disks on separate channels if they have to work at the same time.
The two main channels (primary and secondary ATA) can each run their own protocol, but the master/slave channels cannot do this. If you install two devices which use different protocols on the same channel, you run the risk that the slowest device will determine the speed for the whole channel. The optimal solution, therefore, is to connect your hard disk as the master on, for example, the primary channel, without connecting a CD drive as a slave device.
Look at the following picture. The CD burner is sitting by itself on the secondary ATA channel (Secondary Master), and this is for the sake of the hard disks. The two hard disks have been placed on the primary channel, since they both use the same protocol (ATA/66 in this case). The device’s protocols can be seen on the right in the last two columns (PIO and UDMA mode):
If you use all four ATA connections, it might look like this:
ATA connection
|
Device
|
Primary, master
|
Hard disk 1
|
Primary, slave
|
Hard disk 2
|
Secondary, master
|
CD ROM burner
|
Secondary, slave
|
DVD drive
|
A problem arises when you need to connect two hard disks, in addition to a CD/DVD drive or drives. This is not possible, without compromising on quality. The two hard disks have to placed on the same channel, since CD drives generally operate using a slower protocol. But this does not allow for the optimal utilisation of the hard disks – they should ideally have their own channel, all to themselves, for the sake of multitasking.
This is why motherboards with an extra built-in ATA RAID controller are much more preferable – with these you can install up to 8 ATA devices in the same PC (see Fig. 220. But if you ensure, right from the start, that you put a big hard disk in the PC, this helps.
ATA RAID
The ATA interface can quickly become a bottleneck, as I have just described. I therefore warmly recommend using a motherboard with an extra built-in RAID controller. This doubles the number of possible devices. Many motherboards (like my own from Epox) have both a standard ATA device in the south bridge, and an extra controller (from HighPoint or Promise), and this provides much greater flexibility.
Another option is to buy and external RAID controller which can be mounted in an expansion slot. This will also allow for a further four ATA devices to be connected. For years I used the Fasttrack controller from Promise, which you can see in Fig. 170. If you look carefully you can see two ATA connectors at the top of the card.
Since the ATA limitations have become more pronounced in recent years, most motherboards today can be bought with an extra built-in RAID controller, and that’s the easiest solution.
The RAID controller actually allows for striping of drives (see Fig. 206, but you may also simply use it as an extra ATA controller.
This way one can use two hard disks, which each have an ATA channel all to themselves. Just as the two optical drives each have their own channel also. Perfect! The hard disks run at full speed, and the CD drives have the optimal configuration.
SATA - Serial ATA
The old well-known, parallel ATA system is clumsy and in-flexible. The big ribbon cables take up to much room in the computer cabinet and they reduce the circulation of air. The cables have a fixed length and they make it difficult to mount the harddisks.
Furthermore the PATA-system with master/slave channels is difficult to work with, and the band width is limited.
The successor to the ATA system is called Serial ATA. Here we have an interface using small handy cables with only 7 wires in stead of the big 40/80-wired cables used in the Parallel ATA-interface.
|  |
Serial ATA is a high-speed serial interface in family with Ethernet, USB, FireWire and AMD's Hyper Transport. All these interfaces use a serial technology. They only have two channels: one receiving data and one transmitting them. This can be achieved with a very simple cabling. The data communication only requires 0,25 Volt compared to the 5 Volt of parallel ATA.
The existing PATA system has a limit of 128 GB volume harddisks. This gave problems with the first 160 GB disks. The parallel system only operates with 28 bit data for addressing the disks. It can only adress 228 sectors. Since each sector on the hard disk holds 512 bytes of data, we have 228 times 512 bytes data, which is 128 GB.
To use bigger hard disks, the operating system has to address the sectors directly. In Windows XP this function is called 48 bit LBA, and is it has caused some troubles to have it work. Using Serial ATA, there are no problems with bigger hard disks.
More about Serial ATA:
The controlling logic of Serial ATA is much more sophisticated (and SCSI-like) than in the traditional ATA interface. Serial ATA can process several commands at the same time and re-arrange them for better efficiency.
Figure 231. Cable for Serial ATA.
Some motherboards available in 2004 have SATA controllers based on a bridge. In reality it is just a converter, giving an old-fashioned PATA controller SATA functionality.
These boards take both parallel and serial ATA-disks. This sis great when you have old hard disks, you need to reuse with a new motherboard.
However, this bridged controller gives no room for better bandwidth. So to se better performance from the SATA hard disks, we need a new generation of motherboards without PATA-compatibility.
Chapter 44. Hard disks, ATA and SATA
I am now finally going to describe the ATA interface, which has been mentioned several times earlier in the guide. The ATA interface is used for hard disks (as in Fig. 20, and the motherboard’s ATA controller is built into the chipset’s south bridge, as shown in Fig. 195.
We have also seen, that ATA devices use bus mastering to exchange data directly with RAM. But what does this interface actually consist of? And why do new standards for hard disks keep coming out? We are going to look at that now.
History of the hard disk
It is critical that we have a place to save our programs and data when the PC is switched off. Otherwise it is useless. Twenty years ago, diskettes were used, but their capacity is very limited.
Right back in 1957, IBM introduced the first “fixed disk storage”. It was a big thing with 50 disks that were 24 inches in diameter. This very early hard disk had a capacity of 5 MB – a huge storage space at the time, which cost $35,000 a year to lease. One of IBM’s models was called the 3030, and in the weapons-conscious USA , this led to the hard disk being given the nickname, Winchester disk (a Winchester 3030 was a popular rifle) – a nickname that was also used in Europe for many years.
The first computer with a hard disk was IBM’s RAMAC, which was used during the 1960 Olympics to calculate sports results. A bit later, in 1962, removable disk packs were developed – a forerunner of the floppy disk. In 1964, the CRC algorithm was introduced. It provided greater security by checking and comparing data before and after it was written to the disk. In 1971, the first 8-inch diskettes came onto the market.
But it wasn’t until the middle of the 1980’s that people began to use hard disks in more standard PC’s, and since then development has surged ahead. The capacity of a standard hard disk has actually become a thousand times greater in the period 1990-2000.
The standard user’s need for disk space (e.g. for digital photos, video and music) has grown in step with this, so that 120-250 GB of disk space or more is normal in many PC’s – a figure which will double over the next few years.
Hard disks are constantly being developed which have greater capacity and speed (the two go together, as we shall see), and there is therefore a constant need for new types of hard disk controllers. The companies leading the development are Maxtor, Western Digital, IBM/Hitachi and Seagate.
The physical disk
Hard disks consist of one or more magnetic plates mounted in a metal box. The standard size (as in Fig. 213) is about 10 x 14.5 x 2.5 cm, and such a device can contain hundreds of gigabytes of data. Inside the box, a number of glass or metal plates whir around at, for example, 5400 or 7200 revolutions per minute – these being the two most common speeds.
The read/write heads hover over the magnetic plates, and can transfer data at a tremendous speed:
The actual read/write head is a tiny electromagnet. The magnet ends in a C-shaped head, the shape of which ensures that it virtually hovers above the magnetic plate. Under the read/write head are the disk tracks. These are thin rings packed with magnetic particles. These magnetic particles can be arranged in patterns of bits, which are translated into 0’s and 1’s by the electronics of the hard disk:
When the disk moves under the read/write head, it can either read the existing data or write new data to the disk:
The read/write heads are the most expensive part of the hard disk. When the disk is switched off, the heads are parked in a special area, so that they will not be damaged during transport. In Fig. 216, the cover has been removed from a hard disk, and you can see the uppermost arm with its read/write head.
Tracks and sectors
The individual files are written across a number of disk sectors (at least one), and this task is handled by the file system.
The file system is part of the operating system, which the disk has to formatted with. In Windows 98, the FAT32 file system is used. In Windows 2000/XP, you can also use NTFS. They are different systems for organising files and folder structures on the hard disk. You can read more about the file system in my guide, ”Do it yourself DOS”.
Hard disk development
New hard disk models are constantly being developed, and for each new generation, the capacity becomes greater. This is possible due to new read/write heads and magnetic plates which are more dense. When the magnetic density is increased, hard disks can be produced which have greater capacity for the same number of plates.
Another consequence of higher density is that the disks become faster, since they can transfer more data per rotation. There are simply more bits hidden in each track.
All hard disks have a certain amount of cache installed as 2 or 8 MB of fast RAM, which functions as a buffer. The cache helps ensure that the data gathered by the mechanics of the disk is optimally exploited.
The new and faster hard disks are always followed by new types of interface, since the controller principles have to be upgraded as well in order to handle the large amounts of data. At the time of writing, the fastest ATA interface is called ATA/133, but it is about to be replaced with Serial ATA (see Fig. 221).
The hard disk’s interface
The hard disk is managed by a controller built into the actual unit. This controller works together with a similar controller linked to the PC’s I/O bus (on the motherboard). I showed this setup in Fig. 20, in order to explain the concept of “interface”.
The interface’s job is to move data between the hard disk sectors and the I/O bus as fast as possible. It consists of:
In the ”old days”, interfaces such as ST-506 and ESDI were used. The ATA (AT Attachment) interfaces are based on the IDE standard (Integrated Drive Electronics). The names, IDE and ATA are “owned” by Western Digital, but are used anyway in everyday language.
Enhanced IDE
The IDE standard wasn’t especially fast, and couldn’t handle hard disks bigger than 528 MB. So the ATA standard came out in the mid-1990’s, and is still used today for cheap, high-performance, mass-produced hard disks. ATA is an enhanced edition of IDE, where the interface was moved from the ISA bus to the high-speed PCI bus. In principle, ATA (or parallel ATA) can be used for a number of different devices. The most common are:
ATA was developed as a cheap, all-round interface, designed for the different types of drives.
Host controller with two channels
The ATA interface can be seen as a bus, which is managed by a host controller. Up to four devices can be connected per host controller, and the devices connect directly to the motherboard.
The slightly unusual thing about the ATA interface is that there are two channels, which can each have two devices connected. They are called the primary and secondary channels. If two devices are connected to one channel, they have to be configured as one master and one slave device:
These four channels are standard on today’s motherboards using parallel ATA. Motherboards typically have connectors for two ATA cables, which can each connect two devices (master and slave).
These rectangular, male ATA connectors are placed in a fairly accessible location, and are used to connect the ribbon cables which fit hard disks and CD/DVD drives.
Transfer speeds and protocols
There are many ATA versions. The protocol has been changed over the years, but on the whole, the products arebackward compatible.
This means that you can readily connect an old CD-ROM drive which uses the PIO 3 protocol, for example, to a modern motherboard with an ATA/133 controller. The drive just won’t be any quicker as a result. The shift from parallel ATA/133 to Serial ATA is more profound. Here we use a different type of controller and new cables.
The various protocols have different transfer speeds, as shown in the table below.
Max. theoretical transfer rate
| |
PIO 3
|
13.3 MB/second
|
PIO 4
|
16.6 MB/second
|
Ultra DMA (ATA/33)
|
33 MB/second
|
ATA/66
|
66 MB/second
|
ATA/100
|
100 MB/second
|
ATA/133
|
133 MB/second
|
SATA
|
150 MB/second
|
The transfer speeds listed apply to the interface. Few hard disks can deliver more than 80 MB/second, but even so, it’s still good to have the fastest possible interface. If two hard disks are used on the same controller, or if disks with a large cache are used, there can be a need for big bandwidth for short periods.
With the ATA/66 standard, a new type of ATA cable was introduced. Hard disk cables normally have 40 conductors, but in the new version this is extended to 80, as each wire is balanced by a ground connection. This reduces electrical noise and allows for greater bandwidth.
Parallel ATA setup
If you build your own PC or upgrade it using a new hard disk or CD/DVD drive, it is important that you know the limitations of the parallel ATA system.
Modern motherboards can automatically recognize ATA devices. This means that, in principle, you can install your drive and start the PC, and it should work. You can follow the startup program while it “installs” the drive, as shown in Fig. 223, where two hard disks and CD burner are installed.
In the first four lines, the controller auto detects the four channels for connected devices. It then ”mounts” (configures) the two Maxtor hard disks on the primary channel, and finally the HP burner on the secondary channel. You can read this in the lines below:
Each ATA device has a small area containing jumpers which are used to set whether it is the master or slave device. If the startup is to proceed as painlessly as in Fig. 225, the jumpers have to set correctly on all devices, and of course the cables have to correctly connected.
Multitasking and protocol limitations
But this is not the case if two disks are connected to the same ATA channel. They cannot multitask. Either the master is working, or the slave is working, but not both at the same time. It is therefore best to install two hard disks on separate channels if they have to work at the same time.
The two main channels (primary and secondary ATA) can each run their own protocol, but the master/slave channels cannot do this. If you install two devices which use different protocols on the same channel, you run the risk that the slowest device will determine the speed for the whole channel. The optimal solution, therefore, is to connect your hard disk as the master on, for example, the primary channel, without connecting a CD drive as a slave device.
Look at the following picture. The CD burner is sitting by itself on the secondary ATA channel (Secondary Master), and this is for the sake of the hard disks. The two hard disks have been placed on the primary channel, since they both use the same protocol (ATA/66 in this case). The device’s protocols can be seen on the right in the last two columns (PIO and UDMA mode):
If you use all four ATA connections, it might look like this:
ATA connection
|
Device
|
Primary, master
|
Hard disk 1
|
Primary, slave
|
Hard disk 2
|
Secondary, master
|
CD ROM burner
|
Secondary, slave
|
DVD drive
|
A problem arises when you need to connect two hard disks, in addition to a CD/DVD drive or drives. This is not possible, without compromising on quality. The two hard disks have to placed on the same channel, since CD drives generally operate using a slower protocol. But this does not allow for the optimal utilisation of the hard disks – they should ideally have their own channel, all to themselves, for the sake of multitasking.
This is why motherboards with an extra built-in ATA RAID controller are much more preferable – with these you can install up to 8 ATA devices in the same PC (see Fig. 220. But if you ensure, right from the start, that you put a big hard disk in the PC, this helps.
ATA RAID
The ATA interface can quickly become a bottleneck, as I have just described. I therefore warmly recommend using a motherboard with an extra built-in RAID controller. This doubles the number of possible devices. Many motherboards (like my own from Epox) have both a standard ATA device in the south bridge, and an extra controller (from HighPoint or Promise), and this provides much greater flexibility.
Another option is to buy and external RAID controller which can be mounted in an expansion slot. This will also allow for a further four ATA devices to be connected. For years I used the Fasttrack controller from Promise, which you can see in Fig. 170. If you look carefully you can see two ATA connectors at the top of the card.
Since the ATA limitations have become more pronounced in recent years, most motherboards today can be bought with an extra built-in RAID controller, and that’s the easiest solution.
The RAID controller actually allows for striping of drives (see Fig. 206, but you may also simply use it as an extra ATA controller.
This way one can use two hard disks, which each have an ATA channel all to themselves. Just as the two optical drives each have their own channel also. Perfect! The hard disks run at full speed, and the CD drives have the optimal configuration.
SATA - Serial ATA
The old well-known, parallel ATA system is clumsy and in-flexible. The big ribbon cables take up to much room in the computer cabinet and they reduce the circulation of air. The cables have a fixed length and they make it difficult to mount the harddisks.
Furthermore the PATA-system with master/slave channels is difficult to work with, and the band width is limited.
The successor to the ATA system is called Serial ATA. Here we have an interface using small handy cables with only 7 wires in stead of the big 40/80-wired cables used in the Parallel ATA-interface.
| |
Serial ATA is a high-speed serial interface in family with Ethernet, USB, FireWire and AMD's Hyper Transport. All these interfaces use a serial technology. They only have two channels: one receiving data and one transmitting them. This can be achieved with a very simple cabling. The data communication only requires 0,25 Volt compared to the 5 Volt of parallel ATA.
The existing PATA system has a limit of 128 GB volume harddisks. This gave problems with the first 160 GB disks. The parallel system only operates with 28 bit data for addressing the disks. It can only adress 228 sectors. Since each sector on the hard disk holds 512 bytes of data, we have 228 times 512 bytes data, which is 128 GB.
To use bigger hard disks, the operating system has to address the sectors directly. In Windows XP this function is called 48 bit LBA, and is it has caused some troubles to have it work. Using Serial ATA, there are no problems with bigger hard disks.
More about Serial ATA:
The controlling logic of Serial ATA is much more sophisticated (and SCSI-like) than in the traditional ATA interface. Serial ATA can process several commands at the same time and re-arrange them for better efficiency.
Figure 231. Cable for Serial ATA.
Some motherboards available in 2004 have SATA controllers based on a bridge. In reality it is just a converter, giving an old-fashioned PATA controller SATA functionality.
These boards take both parallel and serial ATA-disks. This sis great when you have old hard disks, you need to reuse with a new motherboard.
However, this bridged controller gives no room for better bandwidth. So to se better performance from the SATA hard disks, we need a new generation of motherboards without PATA-compatibility.
Chapter 45. System software. A small glossary
We have now examined most of the PC’s architecture, from CPU and RAM, to expansion buses, to the hard disk. We still need to look at the motherboard’s built-in system software.
There is software stored on every motherboard. The ROM circuits contain important system routines which help to startup the PC and which hold everything together. The following chapters provide a brief introduction to these topics:
The guide concludes with a glossary.
PC startup
When you switch on the power to your PC, a lot of things happen. You here the noise of the various cooling fans, and shortly afterwards, text starts to scroll up onto the screen. It is the system software which is doing this work.
Remember that the PC cannot do anything unless it receives instructions. Instructions are fragments of programs which are loaded into the CPU, and the CPU starts by executing the system software which is stored on the motherboard. Later, once the PC is up and running, the operating system can fetch instructions (programs) itself from the hard disk; but during startup, the CPU is fed instructions from the ROM code in the motherboard.
That is, the startup programs are stored in ROM circuits. ROM stands for Read Only Memory. These circuits contain data, which can normally only be read. Thus the PC is ”born” at the manufacturer with system software stored in its hardware.
On newer motherboards, however, Flash ROM is used (so-called EEPROM circuits). With these, the data can be changed by the user (BIOS updates). For convenience, these circuits are still called BIOS ROM.
BIOS is important system software, because it is only after these programs have been loaded and executed that the PC’s operating system can be loaded from the hard disk (or alternatively, from a diskette or another drive). This is called the boot process.
Checking the hardware
If POST encounters a fault in the machine, the program will write a message on the screen. If the screen has not yet been made ready, or if the fault is, for example, linked to the video card, the program will normally emit beeps using the PC speaker. The pattern of bleeps and beeps varies for the different BIOS manufacturers, but the pattern indicates where the fault is located. For example, 8 beeps from a BIOS from AMI can mean a fault in the graphics system, while a constant series of short beeps indicates a fault in the RAM when using BIOS from Award. Some motherboards have built in LED’s which can also signal faults (you can actually see these in Fig. 30. The fault messages are always explained in the motherboard manual.
When POST has finished executing, you normally hear a single beep from the speaker, and startup continues. Next the BIOS is loaded for the video card. This leads to the first text on the screen, which is normally the name of the BIOS supplier and the program version.
The startup program is now in the process of checking the various hardware, and generally “bringing the machine to life”. You can make contact with the Setup program at this time, for example by pressing the Delete key once. After this you will see that the ”RAM is being counted”. You can also read which CPU is in the machine. Any error messages (e.g. if the hard disk is not connected properly) can now be seen on the screen.
Try to follow the startup process yourself when you switch on your PC. You can stop the process by pressing the Pause key, so that you have time to read the messages. Below you can see the startup messages for a PC with Award BIOS, which has found 512 MB of RAM.
The startup program installs the other system devices, such as floppy disk and ATA drives, and locates the “logical devices” (such as COM, LPT, etc.). The PCI bus is scanned for devices.
CMOS and Setup
The startup program needs information about the PC’s hardware. However, some of this system information has to be manually entered. This includes things like whether a floppy disk drive is installed, and the actual time and date, etc. Fortunately we don’t have to type in this information every time we start the PC. It is done by the manufacturer, and the information is stored in a small CMOS chip.
CMOS is a special type of RAM, which excels at using very little power. The chip is used as a storage area for the small database of hardware information. The database is necessary for the startup programs, which, for example, use it as a list of the hardware which has to be checked. See also the discussion of ESCD, which is included in the CMOS storage. This is a store containing information about the PC’s Plug and Play compatible devices.
You can correct the settings in the CMOS storage yourself. You might need to do this, for example, if you install a new hard disk. That’s why we have access to the CMOS via the Setup program, which is also stored in the motherboard’s ROM circuits. Setup can be activated during startup by pressing a special key (e.g. Delete).
Figure 235. The Setup program is used to change the settings in the CMOS storage.
Chapter XX. A quick look at Setup
If you want to look at the facilities of the Setup program, you have to activate it while the startup programs are scrolling over the screen.
The Setup program can look a bit different, from one PC to another. Below is the opening menu from my PC:
There are many options, which in this example have been divided into 14 different submenus. I won’t go through the whole system; as most of it you will never use anyway.
But let’s take a look at some of the options the various menus offer, including features, setup and configuration. Even though you won’t need to change these settings on your own PC, they provide a good picture of how the Setup program can be used to adjust and actually program the motherboard in various ways,
Standard CMOS Features
This menu is one of the most fundamental of them all. Here you can change the date and time. Floppy disk drives are so ”unintelligent” that the test program cannot check whether a floppy drive is installed or not. This must therefore be specified.
You can also set which ATA channels are in use. In Fig. 237 I have chosen the setting None, for the two unused ATA channels. This allows a slightly faster startup, since the program doesn’t have to search for devices which don’t exist.
Advanced BIOS Features
Here you can set which device should be used to boot from. It can be the hard disk or the floppy disk, and if you have several built-in hard disk controllers (ATA, RAID or SCSI), you specify which of them should perform the boot operation.
Many of the menu choices allow you to either enable or disable (activate or deactivate) various functions. In the fifth line (in Fig. 238) you can see that I have activated Quick Power On Self Test. This simplifies the POST program’s job, so that the PC can be ready faster.
In Fig. 238, the First Boot Device has been set to the floppy disk drive. That means the PC will try to boot from this if there is a diskette in the drive. This may not be smart, if you are nervous about being attacked by a virus on the boot sector of a chance diskette which happens to be in the drive. It can also be nice to avoid the PC stopping during startup because there is a diskette in the A drive.
If instead you specify that the First Boot Device is HDD-0, the PC will always boot from the hard disk – whether there is a diskette in the drive or not. You may also to let the PC boot from the CD drive. That is fine when installing Windows 2000 or XP.
Advanced Chipset Features
This menu is linked to the chipset, which can be programmed in various ways. For example, there are various advanced settings for the AGP and PCI buses. If you use a USB-based keyboard you can specify that here. Then it will work in 16-bit DOS mode (real mode) as well.
The other settings
I have already mentioned that many users never end up fiddling with these Setup settings. There is therefore no reason for me to go through the other menus in detail. Let me just briefly discuss the main points:
Integrated Peripherals. This menu contains settings associated with the ATA and Super I/O controllers. For example, you can disable the floppy disk controller (FDC), so that a floppy disk drive cannot be connected. If the motherboard has a built-in sound device you might be able to disable it here.
Power management. This menu allows you to set how the various power saving functions should operate. There is nothing to benefit from this. The PC consumes the same energy with or without power management activated. On the hand power management can be quite irritating in daily use.
PnP and PCI Configurations. This menu allows you to allocated IRQ’s for each PCI slot yourself. You can also change the PCI bus timing, should you happen to want to. See Fig. 174.
PC Health Status. This gives you a report on the CPU’s current temperature and voltage, and how fast the cooling fans are whirring (if they are connected in the right way). This menu is used, for example, by overclockers, who are very keen to know that the PC is not burning out.
Frequency/Voltage Control. This menu allows you to set the clock multiplier factor for the CPU, if it allows this, and adjust the voltage for the processor core, AGP system and I/O bus. See also Fig. 123.
Set Supervisor and User password. These menus allow you to choose a supervisor password, which is used to protect the Setup settings. This is used in some schools, where certain students have a tendency to fiddle with the computer’s setup options.
Conclusion
The CMOS storage contains a number of essential items of system data, which are used by the startup programs. The user has the option to change these settings via the Setup program.
Many of the more advanced options are not relevant to normal users like us. They are linked to the controller chips on the motherboard, which can be configured in various ways, but there is no reason to change these settings. The motherboard manufacturer has already configured everything optimally, and they recommend in the manuals that you don’t change anything. But if you are interested in your PC at the hardware level, you should definitely acquaint yourself with the facilities of the Setup program.
Resetting the CMOS storage
If you look at the main menu in Fig. 236, there are options there to reload the standard settings (Load Fail-Safe Defaults and Load Optimized Defaults). You can make use of this if, after playing around, you find that your settings no longer work.
It is a very good idea to write down what you change on a piece of paper – especially the first time you work with Setup. Record the menu and setting you change, and what the value was before you changed it.
If it gets right out of hand, you can always reset the CMOS. You might need to do this, for example, if you set up password protection for Setup, and then forget the password.
The motherboard as a jumper which erases the CMOS data. You move the jumper, start the PC, and the data is erased. You then enter new data and move the jumper back again.
Another method is to remove the motherboard battery. This maintains the CMOS data, so all the data is erased if you briefly remove the battery (which you can ease out of its round plastic holder).
Modern batteries last for many years, but you may find that the battery has to be replaced one day. You’re sure to notice when this happens. The Setup program will ask you to enter the date, etc. – every time you start the PC!
28. The BIOS programs
I have now described how the BIOS programs are stored in the motherboard’s ROM circuits, and how they look after starting up the PC and allow you to ”program” various hardware devices via the Setup program. But that’s not the whole truth about the BIOS. The BIOS is not only used during startup. And there is BIOS in other places, in addition to the motherboard. Let me conclude this examination of the PC architecture by describing the BIOS.
Using the BIOS
In the computer’s infancy, there were no operating systems. Applications (user programs) were written so that they controlled the PC’s hardware directly. Every program, for example, had to be coded to fetch characters from the keyboard and to send characters to the screen. In order to make programming easier, all the program routines that created interfaces to hardware devices were gathered into a library. This collection became the Basic Input Output System – the BIOS.
Today the BIOS is still a collection of program fragments which establish connections to certain hardware devices. The BIOS is still available to programmers, but the Windows operating system prefers to use its own drivers to communicate with hardware. Thus Windows has two ways of accessing each hardware device:
BIOS really has the same function as the drivers; it’s just an older system. Whereas the BIOS routines are placed in the actual hardware, the drivers are placed within the operating system. There is a BIOS routine, for example, which enables the PC to read input from the keyboard. The BIOS is located, as we have seen, in the ROM circuits on the motherboard. But it is also stored on expansion cards in so-called adapter ROM.
The BIOS we find on the motherboard handles all the motherboard’s own devices. External adapters (e.g. video cards) also need BIOS, and this code is, of course, placed in ROM circuits in the device. During startup, all the BIOS is merged and allocated RAM addresses, so that these program fragments are available to the operating system.
Figure 243. The Plug and Play system has its own BIOS, which is loaded into a RAM address.
Thus both the drivers and the BIOS tailor the hardware devices for the operating system, so that everything works together:
16 bit BIOS code
The BIOS routines are part of the very original PC architecture. They were therefore written in 16-bit code which suited the original 8088/86 processors, and which was executed in the slow real mode. The BIOS is the PC’s oldest and most primitive program layer.
Since modern CPU’s, and Windows, are a 32-bit environment, it is not appropriate to use the BIOS routines for anything beyond what is absolutely essential. During normal daily operations, Windows therefore uses its own 32-bit drivers to exchange data with hardware devices. These drivers work much faster, and can be constantly adapted to new hardware.
However, during startup, the BIOS is still important. At that time, the operating system hasn’t yet been loaded, so the startup programs draw on the BIOS. And if you work with a 16-bit operating system (such as DOS), it will be using the BIOS to a large extent.
Advantages of 32-bit drivers
Windows’ drivers can write directly to all kinds of hardware – bypassing the BIOS routines.
One example is the COM ports. If you use the BIOS routines attached to these, you cannot transmit any more than 9600 bits per second (baud) via a modem. But using Windows’ own drivers, much greater amounts of data can be transferred over the COM ports.
Thus in this situation the original BIOS routines are basically unusable. One could easily imagine that the BIOS could be upgraded to be more efficient. But that would presumably break the compatibility. So instead we continue to live with obsolete BIOS, but luckily it has little practical significance.
BIOS upgrades
The BIOS programs can be upgraded. Modern motherboards (as mentioned before) have their BIOS stored in flash ROM, which can be upgraded. You can obtain new BIOS software from your supplier or on the Internet.
To perform an upgrade you first download the new BIOS from the motherboard manufacturer’s web site and save it on a diskette. You then “run” this on the PC in DOS mode.
However, you shouldn’t start to experiment with BIOS upgrades unless you are sure that you have understood the instructions 100%, and that you have obtained the correct version of the BIOS. Otherwise it can cause big problems.
Instead of BIOS
Intel plans to replace the (very) old BIOS system with a new set of programs. The new system is called EFI (Extensible Firmware Interface) and is in it self a complete little operating system. It has a graphical user interface. Where the old BIOS is written in the Assempler language, the new EFI is written in C, making it more easy accessable.
29. The end
We have now worked our way fairly thoroughly through the PC’s architecture. I hope you have really learned something from the examination. The ongoing work is up to you. I recommend you take your time to analyse your own PC. You can learn a lot from that.
Getting help
There are a number of tools you can make use of when you start investigating:
It can also be very practical to have a startup disk with DOS on it. If you load this, you will get access to “pure DOS”, which you can learn a lot from working with.
Search on the Net
I have already mentioned that the Internet is a good source of knowledge on IT subjects. There are an incredible number of English language sites, which specialise in describing, analysing and commenting on various hardware items such as motherboards, processors, etc.
I won’t promote any sites in particular. When I need information myself on a particular topic, I use the Google search engine, and I can find a handful of relevant sites in a matter of seconds. In my experience you can get a lot out of doing this.
If I was to mention a specific site, it would have to be www.geek.com. It is run by Rob Hughes, and every month he sends out a little newsletter, which I can warmly recommend. Rob talks about all the new processors, and developments in the area of RAM, chipsets, etc, and also provides links to other sites. It is very good, and free.
30. Glossary
Fairly early on in the guide I started to explain a number of terms. I will now conclude with even more of the same. Most of these expressions have been used in the guide; here is a brief explanation of them.
AMR. Audio Modem Riser. A standard for small expansion cards which are mounted on the motherboard and which provide connectors for the motherboard’s built-in sound and modem functions. Only used in very cheap PC configurations.
BIOS. Basic Input Output System. Program code which provides simple control over a hardware device.
Bus Master. A controller property, which allows a PCI device to take control over the PCI bus, so that data can be exchanged directly with RAM. CMOS. Complementary Metal-Oxide Semiconductor. Really a name for the process technology used, among other things, for CPU’s. There is a CMOS storage chip on the motherboard which contains a database of information about the motherboard and the other hardware devices. CSA. Communication Streaming Architecture. An Intel design, where the Gigabit LAN controller plugs directly into the north bridge.
DMA. Direct Memory Access. A system which allows an ISA device to move data directly to and from RAM.
DOS. Disk Operating System. A 16-bit operating system from the time before Windows. Can still be installed on any PC.
DRAM. Dynamic RAM. Storage cells which are used for standard RAM modules. Requires a constant refresh signal to remember the data.
ECC. Error Correcting Code. A type of RAM which can correct internal errors which might occur during program execution. Is used for DRAM in servers and in the CPU’s internal cache.
ECP. Enhanced Capabilities Port.
EIDE. Enhanced IDE interface for hard disks. Also called PATA for Parallel ATA.
EPP. Enhanced Parallel Port.
ESCD. Extended System Configuration Data. A list of the installed PCI devices. Included in the CMOS storage.
File system. A system for organising data at the sector level on, for example, a hard disk. E.g. FAT32, NTFS.
IDE. Integrated Drive Electronics. Hard disk interface.
IrDA. Infrared Data Association. Standard for wireless data transfer over short distances using infrared light (like your TV remote control).
Local bus. A bus (e.g. the system bus) which runs synchronously with the clock frequency in a connected device.
LPC. Low Pin Count. An Intel standard which is used, among other things, for non ISA-based Super I/O chips, designed with relatively few pins.
Mode. A state which an interface or a system can work in.
Multitasking. When a system can work on several jobs at the same time.
PCI. Peripheral Component Interconnect. The traditional motherboard’s standard I/O bus.
PCI Express. New standard replacing PCI and AGP.
PIO. Programmed I/O. Protocol for IDE/EIDE interfaces.
POST. Power On Self Test. The part of the BIOS programs which tests the PC during startup.
Protected mode. The 32-bit program state which replaced real mode.
Real mode. A 16-bit state which programs were limited to working in in the first CPU’s.
Registers. Tiny, lightning fast RAM stores, built deep into the CPU. RAID. Redundant Arrays of Inexpensive Disks.
SATA. Serial ATA.
SCSI. Small Computer System Interface. An ”intelligent” expansion bus.
SRAM. Static RAM. A type of RAM which (in contrast to DRAM) can maintain its data without a refresh signal. SRAM is faster and more expensive than DRAM. SRAM is used, for example, for processor caches.
Thank you very much for your attention !
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