My first (usable) computer was a Commodore 64, with 3 registers but a special addressing mode for RAM in the 0x00-0xFF range. It was largely used as 256 bytes of “kinda like a register but not exactly” storage.
Brilliant little machine, the good old 64. You are absolutely right about the zeropage (0x00-0xFF) and the three registers. Two of those three were pretty special and limited however. So, I'd say the C64 (and all 6502 or 6510 based systems) had really only one general purpose register.
