IBM chose the Intel 8088 for the first PC. If they had chosen the Motorola 68000 instead ( As Apple did)  it might have swept the floor with all the competition. The limitation of the 8088 was that it could only handle 64K segments of data. This was not seen as a problem at the time but would come back and haunt them as applications got bigger and bigger. The reasons for the choice are probably complex and revolve on cost versus quality.   Apple however believed that people would be willing to pay extra for the best. They were of course both right.

    The first Apple had just been launched and was selling like hot cakes. IBM, up to then only interested in corporate computer systems wanted something to compete as fast as possible. This at a time when it was calculated that just ordering an empty box from IBM would take six months to deliver. What developed was the first IBM PC from off-the-shelf parts in record time. This made it easy for competitors such as Compaq to make "IBM Compatible" PC's. The only patented device was the BIOS which had to be written from scratch from a set of specifications by newly qualified "IBM Virgin" programmers.

    The 8088 was followed by the 8086, 80286, 80386, 486 and Pentium. The 80 at the beginning got dropped from around the 286 as it became a bit of a mouthful. The Pentium should have been a 586 but Intel didn't like the press naming their products for them and chose a different name to flat foot them. Some other manufacturers did however adopt the 586 name and are now referred to as "Pentium Equivalent". 

    What happened to the 80186 or 186? These chips were produced but went into control devices for washing machines and pop-up toasters but not into PCs. This is what we were told. I do know that our main Biochemistry analysers where I work, had a Data Mananger Computer which had a 186 CPU. It was nothing wonderful but it interfaced with the Analyser and had a keyboard and a green monitor.

    The 386 was the first CPU with used a flat memory structure but by then the damage had been done. DOS and Windows 3.1 was structured to deliver data in chunks of 64K. So the system had to emulate the segmented structure and the speed never reached it's full potential. So Apple was justified in claiming that the speed the CPU operated was not a reliable measure of performance.

    With the introduction of Windows 95 the problem seemed to be finally resolved. However it was still hobbled because of a commitment to backwards compatibility. Apple never bothered with legacy support. Their customers were quite happy to buy a new system and start from scratch each time a newer model came out.

   Windows NT promised the world but needed a lot of, at the time, very expensive memory. (The "NT" stands for "New Technology"). Windows NT 4.5 was superceded by Windows 2000, and Windows XP.  The last two are really NT 5.0 and 5.1 respectively. Don't believe me? Open a DOS box and type "ver". Notice also that the flash screen states "Based on NT Technology" (Which would expand to "Based on New Technology Technology").

   So in theory, with both Apple and PC's using chips with flat memory architecture, the clock speed should be everything. Not so, it is just one consideration. The motherboard is just as important. The chipset, Northbridge, Southbridge, Primary Cache, Secondary Cache, Bus speed (to name but a few) must also be considered. So which is better? I have no idea but whatever you buy nowadays will probably outperform anything that was out there five years ago.

Clock Doubling

   After the 486, the manufacturers introduced clock-doubling. This meant that a CPU running at a BUS speed of either 25 MHz of 33 MHz (depending on the chip) would now run at 50 MHz or 66 MHz. So for example a CPU designated as a 486 DX2 66 runs at 66 MHz with a Motherboard BUS speed of 33 MHz. Therefore if you have an old 486 PC which has an  SX or DX chip running at 25 or 33, the simplest upgrade apart from more memory is to install a 486 DX2 66 chip. This will provide a co-pro and a much faster PC. It's not quite as simple as that because 486's from different manufacturers needed different jumper configurations. The Motherboards do not usually make it obvious what needs to be reset for each CPU. However if you stick to the same manufacturer there should be no problem. Therefore let us say you have an Intel 486 SX 33 (or 25). Replace it with an Intel 486 DX2 66 and it will now run at 66 (or 50). Running CPU's at lower speeds (under-clocking) will do no harm. It's over-clocking that generates extra heat and requires more care.

    Later on a 486 DX4 100 was introduced but this one cannot be substituted in an older board as it runs at a lower voltage and would be fried. Incidentally the 486 I was recently given by a friend has a 486 DX4 100 but it runs at a BUS speed of 33 MHz. Therefore this should really be called a 486 DX3 99 but it isn't. Clock Tripled in this case. All goes to show how when you think you have sussed it out you find there are still things out there to trip you up 8-)