MP/M

MP/M, short for Multi-Programming Monitor Control Program, was a multi-user operating system that Digital Research developer Tom Rolander created in 1979 as a multi-user extension of the company's single-user CP/M. It let several users connect to one computer at once, each from a separate terminal, and let each user run and switch between several of their own programs at the same time, using a priority-scheduled multitasking kernel with memory protection, concurrent input and output through XIOS, and support for print spooling and queueing. Digital Research built versions of MP/M for both 8 bit processors, the 8080 and Z80, and 16 bit processors, the Intel 8086 and 80286, each under its own version name. Originally proprietary, MP/M was later open sourced, with Caldera and then Lineo permitting redistribution and modification of Digital Research's source code starting in 1997.