bert@helix.nih.gov (Bert Tyler) (01/29/91)
> I've heard that the XGA adapter requires a 386SX or better > machine. Any idea why ? It is my understanding (from Jake Richter, who wrote the AUTOCAD drivers that come with that adapter, and who is writing a book on programming the XGA) that the Power On Self Test (POST) software for the XGA adapter that is executed when you power up your PS/2 uses 386-specific instructions, and for that reason you need a 386SX or better. The POST software was written by IBM. It is quite possible that the Windows and OS/2 drivers supplied by IBM for the XGA adapter also include 386-specific instructions. The adapter itself does not appear to require any particular chipset - Jake wasn't aware of the POST restriction when he wrote the Autocad driver, so *he* didn't use any 386-specific instructions. Also, I've written code for MS-DOS that throws my XGA into each of its extended modes and reads/writes pixels to the screen in each of those modes - all using the ancient 8088 instruction set.
ss@sprite.Berkeley.EDU (Srinivasan Seshan) (01/29/91)
In article <868@nih-csl.nih.gov>, bert@helix.nih.gov (Bert Tyler) writes: > I've heard that the XGA adapter requires a 386SX or better > machine. Any idea why ? 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. Srini Seshan ss@sprite.Berkeley.EDU
U39648@uicvm.uic.edu (Darius Vaskelis) (01/29/91)
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 ========================================================================= BITNET: U39648@UICVM | "Don't set fire to strangers." Internet: u39648@uicvm.uic.edu | - Mr. Zarniwoop