An enhanced version of the Zilog Z80 with a 16 bit

architecture, introduced in July, 1987. It added an MMU to

expand addressing to 16Mb, features for multitasking, a 256

byte cache, and a huge number of new op codes (giving a

total of over 2000!). Its internal clock runs at 2 or 4 times

the external clock (e.g. a 16MHz CPU with a 4MHz bus).