Copyright Michael Karbo , Denmark, Europe.
Chapter 1. The PC, history and logic
The PC is a fascinating subject, and I want to take you on an illustrated, guided tour of its workings. But first I will tell you a bit about the background and history of computers. I will also have to introduce certain terms and expressions, since computer science is a subject with its own terminology. Then I will start to go through the actual PC architecture!
The PC is a microcomputer, according to the traditional division of computers based on size.
No-one uses the expression microcomputer much anymore, but that is what the PC actually is. If we look at computers based on size, we find the PC at the bottom of the hierarchy.
The point of the story is that the baby has grown up, and has actually taken the lead! Today, PC’s are as powerful as minicomputers and mainframes were in the past. Powerful PC’s can now compete with the much more expensive workstations. How has the PC come so far?Fig. 1. Data processing in 1970. Digital PDP 11/20.
a short look at the historical background of the modern PC, which originated in
Today the PC is an industry standard. More than 90% of all microcomputers are based on Microsoft’s software (Windows) and standardised hardware designed primarily by Intel. This platform or design is sometimes called Wintel, a combination of the two product names.
But at the time that the PC was introduced by IBM, it was just one of many 16-bit microcomputers. For example, the company, Digital, sold many of their “Rainbow” machines in the middle of the 1980’s, which I have worked with myself. These other machines were not IBM-compatible, but they weren’t very different from IBM’s machines either, since they were all based on Intel’s 8088 CPU. There were actually a number of different types of PC in the 1980’s.Fig. 2. DEC Rainbow from 1982. It costed around Euro 8.000 – then!
But over just a few years, late in the 1980’s, the market got behind IBM’s standards for PC architecture. Using the Intel 8086 and 8088 processors and Microsoft’s operating systems (DOS initially, later Windows), the PC revolution got seriously underway. From that time on, we talked bout IBM-compatible PCs, and as the years passed, the PC developed to become the triumphant industry standard.
In parallel with the IBM/Intel project, Apple developed the popular Macintosh computers, which from the very start were very user-friendly, with a graphical user interface. The Macintosh is a completely different platform from the platform of Windows-based pc’s I am describing in this guide.
The Macintosh has also been released in generation after generation, but it is not compatible with IBM/Intel/Microsoft’s PC standard.
Fig. 3. An almost IBM-compatible PC from 1984.
In the table below you can see the development of the PC and it’s associated operating systems. The PC was actually a further development of the 8-bit microprocessors (like the Commodore 64, etc.), which were very popular until late in the 1980’s.
The computer shown in Fig. 2, is a very interesting hybrid. It marked the transition from 8 to 16-bit architecture. The computer contains two processors: an 8-bit Z80 and a 16-bit 8088. This enabled it to run several different operating systems, such as CP/M and MS-DOS 2. The two processors, each with their own bus, shared the 128 KB RAM. It was a particularly advanced machine.Fig 4. The microprocessor has entered its fourth decade.
If we look back at the earlier PC, there are a number of factors which have contributed to its success:
Initially, the PC was an IBM product. It was their design, built around an Intel processor (8088) and adapted to Microsoft’s simple operating system, MS-DOS.
But other companies were quick to get involved. They found that they could freely copy the important BIOS system software and the central ISA bus. None of the components were patented. That wouldn’t happen today! But precisely because of this open architecture, a whole host of companies gradually appeared, which developed and supplied IBM-compatible PC’s and parts.
In the late 1980’s there was a lot of talk about clones. A clone is a copycat machine. A machine which can do exactly the same things as an original PC (from IBM), and where the individual components (e.g. the hard disk) could be identical to the original’s. The clone just has another name, or is sold without any name.
We don’t distinguish as much today between the various PC manufacturers; but they can still be divided into two groups:
Finally, I just want to mention the term servers. They are special PC’s built to serve networks. Servers can, in principle, be built using the same components that are used in normal PC’s. However, other motherboards and a different type of RAM and other controllers are often used. My review will concentrate primarily on standard PC’s.
The very first microprocessor Intel produced (the model 4004, also discussed on page 26) was 4 bit. This meant that in a single operation, the processor could process numbers which were 4 bits long. One can say that the length of a machine word was 4 bits. The Intel 4004 was a 4-bit processor with a 4-bit architecture. Later came processors which could process 8 bits at a time, like the Intel 8008, 8080, and not least, the Zilog Z80 (a very large number were sold). These were used in a large number of 8-bit computers throughout the 1970’s and well into the 1980’s.
The PC (in the 1980’s) was initially a 16-bit computer. With the development of the 80386 processor, there was a change to the 32-bit architecture which we are still using today.
Now there is a 64-bit architecture on the way, both from Intel (with the Itanium processor) and from AMD (with various Athlon 64 processors). But it is still too early to predict the extent to which the 64-bit architecture will spread into normal, Windows-based PC’s.
Fig. 5. Today’s PC’s use mostly 32-bit architecture.
Our PC’s have “spiritual roots” going back 350 years. Mathematicians and philosophers like Pascal, Leibnitz, Babbage and Boole laid the foundations with their theoretical work.
The Englishman, George Boole (1815-1864), was also a natural talent. He grew up in very humble surroundings, and was largely self-taught.
Another Englishman, Charles Babbage, began developing various mechanical calculating machines in 1823, which are today considered to be the theoretical forerunners of the computer. Babbage’s “analytical machine” could perform data calculations using punched cards. The machine was never fully realised; the plan was to power it using steam.
However, it was only in the 20th century that electronics advanced sufficiently to make practical exploitation of these theories interesting.
In the 1930’ies Atanasoff was a professor of mathematics and physics at
winter of 1939 Atanasoff was very frustrated from his lack of progress. After a
long car ride (Atanasoff was fond of fast cars) he found himself drinking
whisky in a bar (he was fond of scotch as well). Suddenly he had the solution.
A machine built on four principles. It should work on base-two (binary) numbers
instead of base-10 and use condensers for memory. Atanasoff teamed up with a
brilliant young electrician Clifford Berry and later the
Another pioneer was the German Konrad Zuse (1910-1995). He was only 18 when he constructed his own mechanical binary computer called Z1.
During the Second World War Zuse’s computer Z3 was used in the German aircraft industry. It was the first computer in the world to be programmed with software. It is interesting, that Zuse’s computers were developed entirely independent of other contemporary scientists work.
Figur 8. Konrad Zuse. One of the first scientists to produce working computers.
During the war, the Germans also used an advanced code machine (Fig. 8), which the English expended a great deal of effort on “hacking”. They were successful, and this contributed to laying the foundation for the later development of computing.
interesting piece of trivia: In 1947, the American computer expert, Howard
Aiken, stated that there was only a need for six computers in the entire