The Z80 came about when Federico Faggin, after working on the 8080, left Intel at the end of 1974 to found Zilog with Ralph Ungermann, and by July 1976 they had the Z80 on the market.[4] Faggin designed the instruction set to be binary compatible with the Intel 8080[5][6] so that most 8080 code, notably the CP/M operating system and Intel's PL/M compiler for 8080 (as well as its generated code), would run unmodified on the new Z80 CPU. Masatoshi Shima, the principal logic and transistor level-designer of the 4004 and the 8080, under Faggins supervision at Intel, also designed most of the microarchitecture as well as the gate and transistor levels of the Z80 CPU at Zilog, assisted by a small number of engineers and layout people.[7][8]