OpenVMS

OpenVMS (Open Virtual Memory System^[2]), previously known as VAX-11/VMS, VAX/VMS or (informally) VMS, is the name of a high-end computer serveroperating system that runs on the VAX^[3] and Alpha^[4] 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^[5] 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.^[6][7][8][9]

OpenVMS commercialized many features that are now considered standard requirements for any high-end server operating system. These include:

• Integrated computer networking (originally DECnet and later, TCP/IP) ^[10]
• Symmetrical, asymmetrical, and NUMA multiprocessing, including clustering ^[11]
• A distributed file system (Files-11) ^[12]
• Integrated database features such as RMS ^[13] and layered databases including Rdb ^[14]
• Support for multiple computer programming languages ^[15][16]
• An extensible shell command language (DIGITAL Command Language) ^[17][18]
• Hardware partitioning of multiprocessors ^[19]
• High level of security ^{[20][21][22][23]}

Enterprise-class environments typically select and use OpenVMS for various purposes including as a mail server, network services, manufacturing or transportation control and monitoring, critical applications and databases, and particularly environments where system uptime and data access is critical. System up-times of a decade or more have been reported, and features such as Rolling Upgrades and clustering allow clustered applications and data to remain continuously accessible while operating system software and hardware maintenance and upgrades are performed, or when a whole data center is destroyed. Customers using OpenVMS include banks and financial services, hospitals and healthcare, network information services, and large-scale industrial manufacturers of various products.