MP944 / F-14 CADC
The Central Air Data Computer was a flight control system for the F-14 fighter, using the MP944 MOS/LSI chipset developed between 1968 and 1970. This computer processed information from sensors and generated outputs for instrumentation and to control the aircraft. The main operation it performed was computing polynomial functions on the inputs. This chipset was designed by Ray Holt, who argues on his website (firstmicroprocessor.com) that this 20-bit serial computer should be considered the first microprocessor.
Block diagram of the F14A CADC computer. Module 1 performs multiplication, module 2 performs division, and module 3 performs special logic functions. From Architecture Of a Microprocessor.
The architecture of this computer is pretty unusual; it consists of three functional modules: a multiplier, a divider, and "special logic". Each functional unit has a microcode ROM (including an address register) that provides a 20-bit microinstruction, a data steering unit (SL) that selects between 13 data inputs and performs addition, the arithmetic chip (multiply (PMU), divide (PDU) or special logic (SLF)), and a small RAM chip for storage (RAS). Each data line transfers a 20-bit fixed-point value, shifted serially one bit at a time. The main purpose of the SLF (special logic function) chip is to clamp a value between upper and lower bounds. It also converts Gray code to binary[21] and performs other logic functions.[22]
I don't consider this a microprocessor since the control, arithmetic, and storage are split across four separate chips in each functional unit.[23] Not only is there no CPU chip, there's not even a general-purpose ALU chip. Computer architecture expert David Patterson says, "No way Holt's computer is a microprocessor, using the word as we mean it today."[24] Even if you define a microprocessor as including a multi-chip processor, Viatron beat the CADC by a few months. While the CADC processor is very interesting, I don't see any way that it can be considered the first microprocessor.
Intel 4004
The well-known Intel 4004 is commonly considered the first microprocessor, but I believe the TMX 1795 beat it. I won't go into details of how Busicom contracted with Intel to have the 4004 built for a calculator, since the story is well-known.[25] I did a lot of research into the dates of the 4004 to determine which was first: the 4004 or the TMX 1795. According to the 4004 oral history, the first successful 4004 chip was the end of February 1971 and shipped to Busicom in March. TI wrote a draft announcement with photos of the TMX 1795 on February 24, 1971, and it was written up in Businessweek in March. The TMX 1795 was delivered to Datapoint in the summer and TI applied for a patent on August 31. The 4004 wasn't announced until November 15.
To summarize, the dates are very close but it appears that the TMX 1795 chip was built first (assuming the chip was working for the Feb 24 writeup) and announced first, while the 4004 was delivered to customers first. On the other hand, Federico Faggin claims that the 4004 was a month or two before the TMX 1795[17]. However, the TMX 1795 was patented; I assume that someone would have mentioned in all the patent litigation if the 4004 really beat the TMX 1795 (rather than building a demo out of the Four-Phase AL1). Based on the evidence, I conclude that the TMX 1795 was slightly before the 4004 as the first microprocessor built, while the 4004 is clearly the first microprocessor sold commercially. Texas Instruments claims on their website: "1971: Single-chip microprocessor invented", and I agree with this claim.
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