Open Virtual Memory System (OpenVMS), initially known just as Virtual Memory System (VMS), is the name of a high-end computer server operating system that runs on the VAX and Alpha families of computers, developed by Digital Equipment Corporation of Maynard, Massachusetts (DEC was later purchased by Compaq, and is now owned by Hewlett-Packard), and most recently on Hewlett-Packard systems built around the Intel Itanium CPU.
OpenVMS is a multi-user, multiprocessing virtual memory-based operating system (OS) designed for use in time sharing, batch processing, real time (process priorities can be set higher than OS kernel jobs) and transaction processing. It offers high system availability through clustering, or the ability to distribute the system over multiple physical machines. This allows the system to be "disaster-tolerant" against natural disasters that may disable individual data-processing facilities. VMS also includes a process priority system that allows for real-time process to run unhindered, while user processes get temporary priority "boosts" if necessary.