The Zilog Z80 microprocessor. Prefer [game-boy] instead for questions about the Game Boy CPU nicknamed the ‘GBZ80’.
The Z80 8-bit microprocessor was introduced by Zilog in 1976.
Its instruction set is a superset of the intel-8080, with several additional registers and a few backwards-incompatible modifications to instruction timing.
- Z80 Reference Manual (PDF) from Zilog.
- Computer History Museum's oral history of the Z-80 (PDF) featuring the main designers' detailed recollections of its creation.
- Down to the silicon: how the Z80's registers are implemented by Ken Shirriff. There are other good Z80 articles on the same blog site.