The Zilog 80 processor chip was a strong contender in late 70's and early 80's computers such as the Sinclair brands. Running at between 1 and 2 Mhz it was an 8 bit chip with, if I remember correctly, one accumulator and one register. In 1989 it was chosen for use in the Nintendo Gameboy and a souped-up version remained in the 1998 Color Gameboy. It's main competitor in the 80's was the 6502.