Excerpted from message dated 09-20-97, Frank Sexton to Derek Oldfather:
FS>Since the only "standard" comm ports that are defined by the official
  >AT standard are COM1 and COM2, the video card manufacturers don't
  >care about COM3 and COM4 addresses. They figure they're free game. 
  >The addresses for COM3 and COM4 are "de facto" standards in the
  >industry but are not hardcoded into the official AT specs.
Hi Frank--
    I don't think there ever were a set of "official AT specs" - at
least not published by IBM.  (The "ISA spec" is not an IBM document.)
AFAIK, there is no such thing as an "IBM compatible" PC, not even when
built by IBM.
    I have owned seven IBM-built desktop/laptop systems since the first
one in early 1982.  No two of these had identical hardware/software
interfaces.  Prior to the PS/VP, I had purchased the "Technical
Reference" manual (optional at extra cost) for each system.  Each such
manual contained a chapter outlining the hardware/software interface
differences between that machine type and its predecessors!
    I assume that IBM licensees get more complete specifications than
are available to the public.  However, until fairly recently, IBM made
little effort to enforce its PC patents.  Remember the cries of anguish
that went up when IBM decided to enforce the MCA patents, and to require
"back licensing" to the PC patents from anyone who wanted to license the
MCA.  IMO, this was the major cause of the small-computer-press campaign
against the MCA.  Anyway, the lack of available specifications (along
with severe cost cutting) is one reason there are so many adapters and
peripherals that will not work with OS/2.
    Regards,
          --Murray

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 * MR/2 2.25 #120 * The wyse JdeBP seith: "Have a good OS/2 day."
--- Maximus/2 2.02
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