The Free On-line Dictionary of Computing (30 December 2018):

Virtual Memory System
OpenVMS
VAX/VMS
VMS

    (VMS) DEC's proprietary operating
   system originally produced for its VAX minicomputer.

   VMS V1 was released in August 1978.  VMS was renamed "OpenVMS"
   around version 5.5.  The first version of VMS on DEC Alpha
   was known as OpenVMS for AXP V1.0, and the correct way to
   refer to the operating system now is OpenVMS for VAX or
   OpenVMS for Alpha.  The renaming also signified the fact that
   the X/Open consortium had certified OpenVMS as having a high
   support for POSIX standards.

   VMS is one of the most secure operating systems on the market
   (making it popular in financial institutions).  It currently
   (October 1997) has the best clustering capability (both
   number and distance) and is very scalable with binaries
   portable from small desktop workstations up to huge
   mainframes.

   Many Unix fans generously concede that VMS would probably be
   the hacker's favourite commercial OS if Unix didn't exist;
   though true, this makes VMS fans furious.

   FAQ

(http://cis.ohio-state.edu/hypertext/faq/bngusenet/comp/os/vms/top.html).

   Usenet newsgroup: news:comp.os.vms.

   [How does its performance compare with other OSes?]

   (1999-06-03)