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Origins of the Modern PC
Homncruse writes "ComputerWorld dispels myths about the history of modern day computers — or, more appropriately, the invention of the first microprocessor. Contrary to popular belief, 'the [Intel] 8008 was not actually derived from the 4004 — they were separate projects.' In fact, the 8008 concept didn't originate from Intel (though they were eventually granted IP rights.) The article goes on to explain the events leading up to the invention and first intended use of the 8008 (a predecessor to the 8086, etc.), and how Intel was initially uneasy about the venture."
I enjoyed the Blueprint of the Datapoint 2200 enclosure, showing the crowded interior. I guess the caption writer has never seen the inside of a mechanical calculator. Imagine an object the size of a small desktop PC enclosure, entirely stuffed with mechanical linkages. It's truly astonishing.
By comparison, a handful of circuit boards stuffed with SSI and MSI chips was delightfully simple. No moving parts! No lubrication! No wear!
Fossil fuel engines, refridgeration and air conditioning systems have been around a lot longer than that, and there's still no better way to cool off something hot than running a cool liquid around it.
Have you been touched by his noodly appendage?
Tracing the x86 back to the 8008 is a mighty tenuous connection.
There are two very weak links.
First, the 8008 to 8080 transition was a major re-do. Like ten times the speed, an external stack, more. The opcodes were upwardly compatible to a point, but that's about the only similarity.
Next, the 8080 to 808x transition was just as abrupt. 16 bit registers, segments, and more. Again there was a certain backward compatibility, if you converted all the mnemonics and register names, but that was about all.
In the 1970s and early 1980s, before general-purpose personal computers, there was a whole industry for "word processors". These were special-purpose machines which offered text editing, printing, and storage for documents. They replaced typewriters. For the first time, people could edit documents without retyping. Word processors were not intended to be user-programmable; they ran a built-in application. Wang was a big name in that area, as were Datapoint and IBM. The original IBM PC reused the display from the IBM Displaywriter, IBM's family of word processors.
The next step was "shared-logic word processors", where several terminals connected to a central unit, with the central unit having a disk and printer. This was a low-end version of time-sharing. Datapoint introduced ArcNet, so the word processors could send documents to each other. But none of this stuff was user-programmable, although the hardware underneath was a general purpose CPU. It wasn't considered reasonable that users in a typical office could program something as complex as a computer. Also, these machines barely had an operating system; they were usually running the application on the bare machine.
After the IBM PC came out, Wang tried to enter that business. They weren't very successful. I used one of their early 8086 machines, the Wang PIC, which had a scanner. It ran a variant of DOS, which, interestingly, allowed about 800K of user space instead of 640K, because they did the split between RAM and device space at a higher address than IBM did. (The real 8086 limit isn't 640K; it's 1024K minus whatever address space is needed for devices.) It used a completely different (and more rugged) plug-in card design than the IBM PC, and wasn't software-compatible. A nice machine, it just lost out for being incompatible.
So really, PCs are descended from these word processors.
It was Intel's clear intention to allow simple, fully automatic translation of assembly code between one generation and the next. So the fact that the transition from each generation to the next is expressed in large steps does not make it a mighty tenuous connection. To exemplify:
(1) The slow speed of the 8008 required hardware acceleration for parity computation, so the 8008 ALU provided a parity bit in the flags register. That bit lasted all the way through the Pentium line. (Could it remain in X86_64? I no longer work in the assembly language world and do not know.)
(2) The original A,B,C,D,E,H/L register configuration with its byte/word weirdness in the 8008 was still plainly visible in the 16-bit X86 line, and hints of those structures lasted right through IA32, though IA32 does have significant improvements in orthogonality. (This is the genesis of the non-orthogonal register sets that compiler writers complained about all the way through IA32, which are fully rectified only with X86_64.)
The connection is not only not tenuous, but (I claim, having worked with every CPU they built from the 8008 to my current Core2duo) clearly connected by an intentional, nearly unblemished record of source-level backward compatibility for the 40 years of its history.
You do have a good point with respect to the way Intel scheduled its generational developments. When my group at AT&T was debating a project based on i486 DX2/66 and i960CA/CF, the Intel FAEs were exceptionally forthcoming with us about the way Intel developed their processor families. One of the more interesting things I learned was that Intel's X86 families were developed using dual teams, each team leapfrogging the other with successive generations. There was constant discussion among the teams, so often ideas from one would slip into the other.
There is no question that each generation was intended to be as large a leap as possible beyond the last, so you do have a good point about the internal architecture of the processor families.