-=> /* Quoting Murray Lesser to Frank Sexton */ <=-
 FS> Since the only "standard" comm ports that are defined
 FS> by the official AT standard are COM1 and COM2, the
 FS> video card manufacturers don't care about COM3 and
 FS> COM4 addresses. They figure they're free game. The
 FS> addresses for COM3 and COM4 are "de facto" standards
 FS> in the industry but are not hardcoded into the
 FS> official AT specs.
 ML> I don't think there ever were a set of "official AT
 ML> specs" - at least not published by IBM.
FS>How was IBM able to build more than one machine the same if
FS>there were no specs?  I thought they had XT specs and AT
FS>specs that they went by and that these were eventually
FS>adopted by "clone" makers.
He is right, there were official XT spec's but there were no official AT
specs. I am sure there were enough internal specs for manufacturing but
what IBM normally calls official spec's documents are extremely
detailed. The AT only had 2 com ports max so a com 3, 4 etc was up for
grabs. What we call the ISA bus was standardized by IEEE. The AT BIOS
had very narrow parameters and needed a maintenance floppy to set them.
Building that logic it into a chip was done by BIOS cloners Pheonix,
AMI, Award etc.  and was not IBM's idea.
The AT was intended to be short lived.  It had things like hand soldered
piggy backed RAM chips and was a real mess.  A sure indicator that
engineering was overruled by marketing.  I still have one of those 6MHz
beasts in my garage.  It was released because MCA was not ready when the
sales people wanted it but it was supposedly running in the lab on the
day that the AT shipped.  Lots of things in the AT fell through the
cracks, it was all going into the ABIOS and MCA and what became the
PS/2.  The AT caught fire; it was not expected. It lasted two years
instead of the probably planned one year with an 8MHz version and normal
RAM's in the second year. The excess inventory went into an XT-286. The
rest is history.
--Lynn
 * SLMR 2.1a * Clones are people two!
--- DB 1.39/004485
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