Comment by adrian_b
Very impressive work, but most of the work has been necessary because Intel 4004 was not really the first microprocessor, this was just BS propaganda used by Intel to push back by one year the date of the launch of the first microprocessor, to 1971.
The first true (civilian) microprocessor was Intel 8008, in 1972.
Intel 8008 was a monolithic implementation, i.e. in a single PMOS integrated circuit, of the processor of Datapoint 2200, therefore it deserves the name "microprocessor".
The processor of Datapoint 2200 had an ugly architecture, but there is no doubt that it was a general-purpose CPU and traces of its ISA remain present in the latest Intel and AMD CPUs.
On the other hand, the set of chips that included Intel 4004 was not intended for the implementation of a general-purpose computer, but it was intended just for the implementation of a classic desktop calculator, not even a programmable desktop calculator.
This is the reason for the many quirks of Intel 4004, e.g. the lack of instructions for the logic operations, and many others that have increased the amount of work required for implementing a MIPS emulator suitable for running Linux.
Even if Intel 4004 was intended for a restricted application, after Intel has offered to sell it to anyone, there have been many who have succeeded to use it in various creative ways for implementing microcontrollers for the automation of diverse industrial processes, saving some money or some space over a TTL implementation.
In the early days of the electronics industry it was very normal to find ways to use integrated circuits for purposes very different from those for which the circuits had been designed. Such applications do not make Intel 4004 a true microcontroller or microprocessor. Very soon many other companies, and later also Intel, have begun to produce true microcontrollers, designed for this purpose, either 4-bit or 8-bit MCUs, then Intel 4004 has no longer been used for new designs.
I'm glad to see the Datapoint 2200 is getting attention, but by reasonable definitions of "microprocessor", the Intel 4004 was first, the Texas Instruments TMX 1795 was second, and the Intel 8008 was third. It seems like you're ruling out the 4004 on the basis of "intent" since it was designed for a calculator. But my view is that the 4004 is a programmable, general-purpose CPU-on-a-chip, so it's a microprocessor. Much as I'd like to rule out the 4004 as the first microprocessor, I don't see any justifiable grounds to do this.
Intel's real innovation—the thing that made the microprocessor important—was creating the microprocessor as a product category. Selling a low-cost general-purpose processor chip to anyone who wanted it is what created the modern computer industry. By this perspective, too, the 4004 was the first microprocessor, creating the category.
My article in IEEE Spectrum on this subject goes into much more detail: https://spectrum.ieee.org/the-surprising-story-of-the-first-...