Midrange computers were once called minicomputers. They have capacities in between desktop and mainframe computers, and sizes between a 19" color TV and a large refrigerator. Historical firms in this market were Data General, Digital Equipment Corp. (DEC), IBM, Prime. Compaq (via DEC merger) and IBM now dominate this market. Compaq (via DEC merger) makes and sells VMS, IBM makes and sells OS/400. Compaq bought and merged with DEC a few years ago and acquired VMS.
Data General (DG) was a firm that made minicomputers and their operating systems. It was acquired by EMC. DG's main operating systems (OSs) were AOS/VS and DGUX. Both systems are in decline. As with other software in this situation, legacy system users still need aid and support, so users are working together to keep systems running.
OS/400 is the operating system used on IBM's AS/400 (now renamed "System i5") computers. OS/400 and AS/400 were launched in 1988. OS/400 is now known as "i5/OS".


Virtual Memory System, a multi-user, multitasking, virtual memory operating system that runs on the VAX and Alpha lines of minicomputers and workstations, originally developed by Digital Equipment Corporation. VMS was introduced in 1977 and the first customer version shipped in 1978 along with the first VAX minicomputer. The operating system was renamed to OpenVMS in the early 1990's. In 1998, Compaq acquired DEC. Compaq announced the port of the OS to the Itanium Processor Family in 2001. Subsequently, Hewlett Packard aquired Compaq and has maintained roadmaps for the OS, committing to the Itanium port, and they successfully demonstrated OpenVMS booted on an Itanium in early 2003. FreeVMS is an initiative to rewrite the OpenVMS operating system and associated utilities under a public license.
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