I came across an article that said CP/M came out in April 1974. I remember using this OS in the microcomputer world in the late 70ās; early 80ās. It came from PL/M, (Programming Language for Microcomputers) later renamed CP/M(Control Program for Microcomputers). Iām not sure what its legacy is though as far as I can recall it was wrapped up in litigation for quite some time. It was used in the 8-bit world but not sure what it's role was in the early PC world!
Happy computing, Murray š