CP/M is an acronym for "Control Program for Microprocessors". It was one of the earliest operating systems for Personal Computers.
CP/M was designed by Digital Research for use with the Intel 8080 based microprocessors, originally single tasking, 8-bit, for up to 64k of RAM. Later versions were capable of multi-user operation and 16 bit processors (see also CP/M-86
It was commonly used from the mid 1970's until the mid 1980's. As an early operating system it was prehistoric compared with those of the 1990's and beyond. Although it was primitive, it was also remarkably simple and uncomplicated to use. In common with computing during that period, the persons who made the best use of it had some formal computing science knowledge to install, use and maintain CP/M systems.
Most users favored CP/M and it was the closest to an industry standard at that time. It went through some versions as microprocessors improved, and was a clear rival to Microsoft's MS-DOS but fell out of use because IBM changed to MS-DOS as its chosen operating system for IBM PCs.
This was what set in motion Microsoft as an operating system provider and was ultimately the demise of compact and manageable operating systems for Personal Computers until Microsoft's grasp on them was loosened somewhat. So, ultimately, part of the blame can be laid at the feet of IBM.
"I much prefer the editor of CP/M than MS-DOS. Makes batch files a breeze to write."