2 ms·
The 8080 has 7 registers and a single addressing mode for accumulator-based instructions (which is most of them), therefore base-8 organization is pretty natura
by bonzini 3y ago
The 8080 has 7 registers and a single addressing mode for accumulator-based instructions (which is most of them), therefore base-8 organization is pretty natural. Likewise for 8086 which has 8 registers and 8 ways to use registers to form an addressing mode (with absolute addressing and three different displacement modes, there would be 8*3+1=25, but they sacrificed [BP] to fit everything in MOD={00,01,10}). Of course one wonders if the choice of 8 registers and 8 addressing mode was due to some kind of fixation with base 8, or vice versa.
Compared to the 6809, the 6502 or the 68000, the biggest reminiscence of the Z80 is the difference between AX/CX/DX/BX having 8-bit parts and SI/DI/SP/BP not having them. Though the low/high parts of IX and IY were accessible on the Z80 via undocumented opcodes (maybe even SP? I don't remember).