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From: U39648@uicvm.uic.edu (Darius Vaskelis)
Newsgroups: comp.windows.ms
Subject: Re: IBM's XGA and non-386 PCs
Message-ID: <91028.214630U39648@uicvm.uic.edu>
Date: 29 Jan 91 03:46:30 GMT
References: <868@nih-csl.nih.gov> <1991Jan29.005123.12066@agate.berkeley.edu>
Organization: University of Illinois at Chicago
Lines: 38

In article <1991Jan29.005123.12066@agate.berkeley.edu>, ss@sprite.Berkeley.EDU
(Srinivasan Seshan) says:
>Does the XGA run in a 55SX?  I had assumed that it was a 32bit MicroChannel
>board and needed a model 70 or higher.
>
>I hope I'm wrong since I have a 55sx.

The IBM PS/2 XGA Adapter/A is a 32-bit Microchannel board, but it does in fact
run in 16-bit slots.  (with some performance degradation, of course!)

It requires a 386SX or better processor not only because it has a few 386-
specific instructions during POST, but because it maps graphics WAY up high in
memory.  As in, around the 3G or 4G boundaries!  The 286 only addresses 16M
directly, and 1G = 1024M.  It does this for the 640x480 mode with 65536 colors.
You can also have MULTIPLE XGA adapters in the system, each mapped to another
area way up high.

Just as a note: owners of 80286 PS/2s are not TOTALLY out of the picture.
Seems that if you get one of those "rip out yer old 80286 and stick in a board
with a 386SX in its place" upgrades, an XGA will work.  I have not verified
this myself, so don't bitch at me if it don't work.  Also, you can apparently
use an XGA if you use one of the Aox MicroMASTER 386 upgrades.  However, it
currently will only allow the XGA to run in its lower performance non-bus-
mastering mode (the current Windows driver) but will NOT work in the full
bus-mastering mode (the current OS/2 Presentation Manger driver).  This is due
to some kind of Aox MicroMASTER 386 vs. IBM XGA bus mastering conflict, and
Aox claims that they are working on it WITH IBM.  Just as a note, the Aox
(because of almost total control of the Microchannel bus) MicroMASTER cards
have conflicts with almost all bus-mastering cards, and Aox is working on it
with IBM.  Seems that in Aox's quest for performance, they upped the ante on
bus-mastering and did it somehow better than everyone else, but in the end it
makes it not entirely happy with the existance of other bus-masters.  (This is
a paraphrasing of a conversation with an Aox technician.)

- Darius
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