OpenVMS is an operating system, which Digital Equipment Corporation (DEC) originally developed for their VAX servers. Later, it was ported, and now also runs on DEC Alpha and Itanium-based systems. It is a 32 bit operating system. When it was published in 1977, it was one of the first of its kind. OpenVMS is capable of supporting many concurrent users; each user is able to run several programs at the same time. It was also one of the first operating systems with a Graphical user interface, the VAXstation was a very popular workstation at the time. OpenVMS uses virtual memory, and was originally developed as a time sharing, batch processing system. It was made for transaction processing, and is a real-time system. The jobs users submit can have a higher priority than those of the operating system. The operating system offers high availability through clustering: The system load can be distributed over multiple computers. That way, the system is "disaster-tolerant": One machine that fails will not shut the operation down.