The short answer is that IRIS Performer 2.0 is the latest
  all-platform release and 2.1 is the InfiniteReality (all flavors -
  Onyx, Onyx2, iR Reality) release.  If you are doing development for
  an application targeted primarily at an InfiniteReality graphics
  platform using InfiniteReality features, you should buy 2.1.  You
  can run 2.1 on any platform running IRIX 6.2 or later, but its only
  benefit over 2.0 was features for the InfiniteReality graphics
  platform.

  IRIS Performer also creates and ships binary compatible bug-fix
  upgrades for the execution environment of the main releases.  These
  maintenance releases have a third field in their number string and
  are binary compatible with the base release.  These upgraded
  execution environments include the optimized DSOs and demo
  executables and are shipped with IRIX releases and made available
  for older IRIX releases through patches.  The following table lists
  the latest versions of our releases and the version of IRIX that
  they shipped with and the corresponding patch number.

  Performer Maintenance Releases:
  
    performer_eoe   shipped in IRIX  available in Patch  for IRIX Releases
    -----------------------------------------------------------------------
*** 2.0.4/2.1.2(*)	6.4		1696		 6.2 and later
    2.0.3/2.1.1(*)	6.3	
    2.0.2				1347		 6.2 and later
    2.0.1		6.2

  
  (*) The 2.1.X upgrades are included as 2.1 compatibility subsystems 
    inside the corresponding 2.0.X version.  This is done to allow upgrades
    for both releases to ship inside IRIX.
  (***) this is the latest maintenance version check it out!

  All InfiniteReality systems (Onyx, Onyx2, ir Reality) running IRIX
  6.2 or later should use IRIS Performer 2.1 (eoe and dev).  Note
  that Performer 2.1 was originally only officially supported on Onyx
  InfiniteReality systems and is only of benefit on those system or
  for doing development for those systems.  Other systems and
  projects not targeted at InfiniteReality should use 2.0 eoe and 2.0
  dev,  plus the latest eoe upgrade or patch as indicated above.

  Patches available for IRIS Performer development subsystems: (also
  see later section on patches)

  There have are 2 patches available for the Performer 2.0
  development subsystems (sample source code, header files, debug and
  static libraries) that correspond to the 2.0.2 eoe maintenance
  release:

  patch 1392 IRIX 6.2 and later
  patch 1414 for IRIX 5.3 (contains dev and eoe)

  These patches are for the 2.0 development subsystems _only_.  Do
  not attempt to install them if running any other base release for
  development.