Back then, memory was only one cycle away, so was practically registers. This is why the 6502 zero page was so important. 6502 instructions took very few cycles

Back then, memory was only one cycle away, so was practically registers. This is why the 6502 zero page was so important. 6502 instructions took very few cycles, so you could move a zero-page byte to the accumulator in 3 cycles, sometimes 2, and is why a $25 6502 could match a $200 Z80. Z80 had a faster clock, but instructions took loads of cycles. Nowadays that is OK, but Z80 did not pipeline. It had fancy looping instructions, but they ran slower than the loop would have.