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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).