The CLC - clear carry - instruction predates the 4004. The PDP-11 for instance used it. I think you're seeing patterns that aren't really there. One thing the

The CLC - clear carry - instruction predates the 4004. The PDP-11 for instance used it. I think you're seeing patterns that aren't really there. One thing the 4004 and 8008 do have in common is a similar floor plan for the chips. They both have the ALU on the left, data bus along the top, instruction decoding in the middle, registers on the right, and on-chip stack on the right. Other processors of that era (e.g. 6800, 6502, 8080) have very different layouts so it's not just coincidence. Texas Instruments produced the TMC 1795, a chip equivalent to the 8008 (before the 8008), and it also has a completely different layout. If you look lower-level, at e.g. the ALU implementation or the register implementation or the pin drivers, there's less similarity. I would have expected they would essentially cut-and-paste some of these low-level pieces, but they are more different than I would expect.