Comment by rbanffy
13 years ago
I remember the Z80 felt distinctively more sluggish than the 6502 (I had an Apple II with a Z-80 Softcard in it so it could run CP/M). Now I know why.
13 years ago
I remember the Z80 felt distinctively more sluggish than the 6502 (I had an Apple II with a Z-80 Softcard in it so it could run CP/M). Now I know why.
No you don't, this was a clever optimization not a performance degrading hack. It was possible to save half the ALU transistors "for free" so the designer did. The for free bit is important. The Z80 ran a superset of the 8085 instruction set at equal or greater speed, but the 8085 had an 8 bit ALU.
The minimum time of an instruction to execute on the 6502 was 2 clock cycles. The maximum is 7, IIRC. On the Z80, it's 4, with the maximum being about 30.
This has, of course, little to do with the width of the ALU.