The 8080 is often said to be the "first truly usable microprocessor". Its predecessor, the first 8-bit microprocessor [[Intel 8008]], had a rigid seven-level address call stack instead of a flexible Stack Pointer. The 8008 instruction set was itself based on the CPU board, built out of dozens of TTL chips, of the Datapoint 2200 computer. [https://www.righto.com/2023/08/datapoint-to-8086.html Source]
Despite what its their naming suggestssuggest, the Intel 8008 and [[Intel 4004]] were separate projects with distinct architectures and purposes. The 8008 was not an upgrade or evolution of the 4004.
See: [https://www.righto.com/2016/12/die-photos-and-analysis-of_24.html Die photos and analysis] [https://www.righto.com/2017/02/reverse-engineering-surprisingly.html The ALU] [https://www.righto.com/2017/03/analyzing-vintage-8008-processor-from.html The counters] [https://www.righto.com/2020/11/reverse-engineering-carry-lookahead.html The carry-lookahead circuit] 8008 microprocessor reverse engineered