RISC/os is a discontinued UNIX operating system developed by MIPS Computer Systems, Inc. from 1985 to 1992, for their computer workstations and servers, including such models as the MIPS M/120 server and MIPS Magnum workstation. It was also known as UMIPS or MIPS OS. Because of its early UNIX heritage, RISC/os was limited in comparison to modern UNIX variants – for example, even the last releases of RISC/os did not support shared libraries. In July 1992, Silicon Graphics purchased MIPS Computer Systems for $220M. Support for RISC/os was subsequently phased out.