Ping Huang <pshuang@sgi.com> writes:

  If you don't know what release of IRIX you are currently running,
  the SGI admin FAQ explains how to find out.

  IRIX 5.3 is the current release on systems with the R2000 and R3000
  CPU's and the Crimson with GTX graphics; it is the last release
  which will support these systems.  IRIX 5.3 was first released in
  early 1995.

  IRIX 6.2 is the current release on Crimson with non-GTX graphics,
  Indigo R4000, Indy, {Indigo2,Onyx,CHALLENGE}, POWER
  {Indigo2,Onyx,CHALLENGE}, and {Indigo2,Onyx,CHALLENGE} R10000
  systems; note that this list includes most of the installed base.
  IRIX 6.2 was first released in March 1996.

  IRIX 6.3 is the current release on O2 systems.  IRIX 6.3 was first
  released in September 1996.

  IRIX 6.4 is the current release on the Origin 200 and 2000 and the
  Onyx2 systems.  IRIX 6.4 was first released in late 1996.

  (The reason the phrase "was first released" is used is that SGI
  often re-releases a version of IRIX without renumbering, to make
  changes to add support for new hardware models.  For example, the
  latest re-release of IRIX 6.2 as of December 1996 is "IRIX 6.2 with
  Indigo2 IMPACT 10000", released June 1996.)