1976: CP/M - History of Desktop OSs
"Control Program/Monitor" was the first widely used mass-market operating system for microcomputers that were affordable enough to be purchased by the general public. Developed by Gary Kildall at Digital Research (initially Intergalactic Digital Research), the operating system was written in Kildall's own original PL/M (Programming Language for Microcomputers) and designed to run on an Intel Intellec-8 development system.
The OS became widely popular due to its application portability between different computer and hardware types and was targeted especially at 8-bit Intel 8080 and Zilog Z80-based computers. It integrated a BIOS, a BDOS (Basic Disk Operating System or BDOS), as well as a CCP (Console Command Processor). Possibly the best known computers to run CP/M were the Amstrad PCW (also called the "Joyce" in some markets), the Amstrad CPC 464 and 664, which included the software by default with the 3-inch floppy drive, and the Commodore 128. CP/M was maintained until 1983. Digital Research was sold to Novell in 1991.