S-100
From Computer History Wiki
The S-100 bus was designed for 8080 and 8085 but mainly used in many Z80 systems. Being well defined it allowed many manufacturers to produce boards and cases for it, which made manufacture and expansion of a system very easy. Most used CP/M as the operating system on them.
S-100 is short for Standard 100, according to an advertisement by Cromemco on page 2 in the November 1976 issue of BYTE magazine.
