What is VMS?

Recently I had a conversation with a account manager of a large software company who never heard of VMS.

VMS is an old operating system, but it is still used in a lot of companies.


VMS is an operating system, developed in 1977 by Digital Equipment Corporation (DEC). The name VMS means Virtual Memory System.

The first version ran on a 32-bit VAX-11/780 (also a DEC machine). VMS was rewritten in 1992 for DEC's 64-bit Alpha processor. From that moment on, the name was changed in OpenVMS. DEC was taken over by Compaq in 1998 and in 2001 VMS was ported to Intel's Itanium (IA-64) processor. Compaq was taken over by HP in 2002, but OpenVMS still exists, on Alpha and on Itanium systems.

OpenVMS is known as a robust and stable operating system. Sometimes people joke that the uptime of Windows is measured in days, of UNIX in months, but of VMS systems in years.

At the hackers conference DEFCON9, 4300 hackers were present. None of them was able to break in into an OpenVMS system running an HP Secure Webserver. The system was declared "cool and unhackable" by the hackers.


OpenVMS file systems consist of separate disks, just like Windows. OpenVMS contains a Record Management System which supports several file types (stream, sequential, relative and indexed files). This enables 'native' basic database functionality built in the filesystem.

OpenVMS has clustering possibilities way ahead of UNIX and Windows. For instance, in VMS clusters it is possible to work on the same file from two nodes, because the cluster supports two systems sharing the same disk (over SCSI).

Batch processing in OpenVMS is also better supported than in UNIX or Windows.

OpenVMS has a concept called "logical names". Logical names are system variables referring to a disk, a directory or file, or that contain other specific information. For instance the logical SYS$SYSDEVICE contains the system's bootdevice.

In OpenVMS files have version numbers. This way errors can easily be corrected. A directory listing is shown below:


The number behind the ; states the version of the file. When a file is changed by accident, the previous (original) version can be copied back easily.

Just like UNIX has shell scripting, VMS has the DCL language. The possibilities of both languages are comparable.


VMS is an expensive operating system. The price was always much higher than UNIX or Windows (and Linux of course).

TCP/IP was not natively implemented in VMS for a long time. Still, a separate product is needed for TCP/IP (the native networking technology is DECnet).


Because of the robust properties and the good security, VMS is often used in:

  • Production (automotive, steel and aluminum production, SCADA systems, etc)
  • Medical
  • Defense
  • Space
  • Secret services
  • Telecommunications (until recently, most SMS test-message systems were based on VMS)
  • Nuclear
  • Financial institutions
  • Chemical industry

This entry was posted on Friday 02 February 2007

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Sjaak Laan

Recommended links

Ruth Malan
Gaudi site
Esther Barthel's site on virtualization
Eltjo Poort's site on architecture


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