CP/M

Control Program/Monitor, and later known as Control Program for Microprocessors, (CP/M) was an single user operating system developed for microcomputers, and became popular both with small businesses and for home hobbyists. Designed by Gary Kildall, it emphasized a small memory footprint and a reliable file system as floppy disk systems were becoming more widely used in the mid 70s. CP/M reached its peak level of popularity later in the late 70s and very early 80s before having its market largely displaced by DOS and its variants.

The early history of CP/M is a little cloudy, but it's generally agreed that the first version was completed by Kildall and his partner John Torode sometime in 1974. By 1975, Kildall had formed a new company called Digital Research, Inc. (DRI) and was selling the software. Originally CP/M was targeted on Intel 8080 chips, but was ported (often by vendors who licensed the system) to the similar Zilog Z80 and Intel 8086 architectures among others microchips. CP/M became a sort of lingua franca for microcomputers, and many small home systems in the late 70s and early 80s touted being CP/M compatible to tap into that extensive software ecosystem as well as the vendor's proprietary software.

Famously, IBM approached DRI in 1980 on Bill Gates suggestion to use a version of CP/M for their new personal computer. After failing to reach an agreement, IBM returned to Gates and contracted to have Microsoft produce a new operating system. Microsoft actually purchased a modified CP/M clone called 86-DOS and used it as the base for PC-DOS which shipped with the first IBM PC in 1981. The Atari ST was also envisioned as running CP/M but ultimately Atari opted to license DRI's graphical system GEMDOS.

The arrival of DOS led to the slow evaporation of CP/M from the marketplace, leading even DRI to slowly migrate their CP/M releases into a fully DOS compatible system, DR-DOS. The last official full CP/M version was released by DRI in 1983.

Most CP/M system were text only, as there was no common graphic card standards for the system until 1982; subsequently most games for CP/M were text only or used only simple graphics. Software written for CP/M typically was distributed on either 5.25" or 8" floppies.