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).