System Compatibility

 The following flags are used in TECH Help! to refer to differences in
 various IBM-compatible platforms.  When you see one of these items, it
 indicates that the function, variable, port, or feature under discussion
 is specific for that particular version of the PC and probably does not
 apply to other versions (especially older versions).

       AT applies to the IBM AT or compatible: based on an 80286 CPU
      286 applies to any computer based on the 80826, including the XT-286,
          PS/2 models 50 and 60, and various clones.

     PS/2 applies to IBM PS/2 only ("real" PS/2s based on 286/386 CPU)

      386 applies to PCs which use 80386 CPU (supports virtual 86 mode)
      486 applies to PCs which use 80486 CPU (has build-in math chip)
  Pentium applies to PCs which use Pentium (80586) CPU
          In general, all 386+ CPUs are in same category, software-wise.

    PC/XT applies to either the PC or XT, but specifically NOT the AT
       XT applies to the XT (mostly refers to differences in disk BIOS)

     PCjr applies ONLY to the PCjr (in other words, ignore it)

   (none) when no reference is given, the topic applies to all members of
          the PC family, and has remained compatible through the variations
          in ROM-BIOS firmware and PC (and clone) hardware.

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