5 ms·

A Lost IBM PC/at Model? Analyzing a Newfound Old Bios

115 points by TMWNN 1y ago

mrlonglong 1y ago
Excellent write-up.
- viler 1y ago
  Appreciated, thanks!
drfuchs 1y ago
Any chance it was for the "IBM Personal Computer AT/370" that nobody remembers (perhaps because nobody used)?
- viler 1y ago
  That was one option I thought of at first (mentioned in the first section), but the info I found indicated that the /370 models used the same firmware as the "plain" 5170s - if there were any BIOS extensions, they were probably somewhere on the add-on cards. The AT/370 also had 512K of on board RAM, while this BIOS seems to indicate 640K.
- m463 1y ago
  I remember that. I think it ran VM/SP or whatever it must have been called. I recall the 370 part was on a card.
  - ForOldHack 1y ago
    3 cards. CPU/Memory and communications cards.
- TMWNN 1y ago
  Article discusses and dismisses that possibility
- helf 1y ago
  [dead]
- ForOldHack 1y ago
  Details: The IBM AT/370 used standard bios on the motherboard, and the two 68k custom cards had their own bioses. The 68ks were very heavily modified by one of the motorola engineers. Its the second version of the AT Bios that was disgusting was verion 2, that ran on 6mhz 286s and prevented you from swapping the crystal for a 16Mhz/8Mhz speed up. The first version had bugs, and the third version was for the 8Mhz machines. ( still a few bugs ). This is the AT/370: https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compatible_systems https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compati... https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro-370/ https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro... https://anycpu.org/forum/viewtopic.php?f=22&t=350 https://anycpu.org/forum/viewtopic.php?f=22&t=350 There was one additional model of the IBM AT: THE IBM XT/286: An AT class mother board in an XT sized case. https://www.dosdays.co.uk/computers/IBM%20PC-XT-286%20(5162)/ibm5162.php https://www.dosdays.co.uk/computers/IBM%20PC-XT-286%20(5162)...
- drfuchs 1y ago
  Oops. Anyway, I remember attending a talk by one of the IBM engineers back when they first released the XT/370. He said that they looked at all possible ways to integrate their production line as a kind of secondary track off of one of the main production lines for the PC/XT, but the most economical option ended up being a separate facility that would receive normal pallets of regularly boxed, end-user XTs from the main factory, unbox them, make the mods, and pack them back into XT/370-labeled boxes for shipping.
- kjs3 1y ago
  Plenty of people remember, and used, them. Just not people who tend to hang out here. I knew several IBM VM dev types who had them as light dev/remote mainframe access machines, usually at home. They were popular enough there was a followon product: the PC/390 which was the same idea, more advanced processor, based on a PS/2 microchannel platform (and, AFAIK, OS/2). You want really obscure? Unisys had the same idea with the "Micro-A", which was a PC running OS/2 with a coprocessor card with a single chip implementation of an A-series mainframe. I know of 2, possibly 3, still around.
eek2121 1y ago
Back when I was a teenager, I would have absolutely gone down a rabbit hole like the author did. From "Upgrading and Repairing PCs" to reading all the technical manuals, usenet, etc. I definitely nerded out over this stuff! Glad to see folks still take an interest. These days, I've an acquired brain injury. Between that an old age, it was a bit hard to read, but also, just a little bit familiar, so I enjoyed it. Now I am expecting "256 color VGA programming in C" to resurface at some point! :D Old hardware was always so much fun...
- mrandish 1y ago
  256 colors? VGA? Bah! You kids with your newfangled graphics modes. 320 x 200 CGA and 16 colors is more than enough. See the linked "8088 MPH" video for proof: https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-all-your-emulators/ https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-al...
  - m463 1y ago
    > 320 x 200 CGA with the opposite of smooth scrolling - video off during text scrolling. BLINK! kind of like the crazy blinking ancestor of vsync off
  - vardump 1y ago
    320 x 200 CGA allows you to have only 4 colors at a time. Of course you can change the fixed palette on a certain scanline to have more colors. See for example California Games.
    - 1313ed01 1y ago
      160x100 CGA low resolution could do 16 color (bit of a hack, but semi-official). And then there were tricks to get more colors in higher resolutions as well, especially if you used the TV output instead of a CGA monitor. https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-illustrated/ https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...
sema4hacker 1y ago
My OCD tendencies would have made me label the one chip ..ODD.. instead of .ODD... just for a little more symmetry.
notherhack 1y ago
The blog refuses connections from VPNs. https://archive.is/Ef75R https://archive.is/Ef75R
- viler 1y ago
  Strange... if it does, that's not my doing - it seems to work fine with the VPN I use, but I'll look into it. Thanks for the heads up.
breakingcups 1y ago
I love this sort of digital archeology

115 points by TMWNN 1y ago

mrlonglong 1y ago

Excellent write-up.

viler 1y ago
Appreciated, thanks!

drfuchs 1y ago

Any chance it was for the "IBM Personal Computer AT/370" that nobody remembers (perhaps because nobody used)?

viler 1y ago
That was one option I thought of at first (mentioned in the first section), but the info I found indicated that the /370 models used the same firmware as the "plain" 5170s - if there were any BIOS extensions, they were probably somewhere on the add-on cards. The AT/370 also had 512K of on board RAM, while this BIOS seems to indicate 640K.
m463 1y ago
I remember that. I think it ran VM/SP or whatever it must have been called. I recall the 370 part was on a card.
- ForOldHack 1y ago
  3 cards. CPU/Memory and communications cards.
TMWNN 1y ago
Article discusses and dismisses that possibility
helf 1y ago
[dead]
ForOldHack 1y ago
Details: The IBM AT/370 used standard bios on the motherboard, and the two 68k custom cards had their own bioses. The 68ks were very heavily modified by one of the motorola engineers. Its the second version of the AT Bios that was disgusting was verion 2, that ran on 6mhz 286s and prevented you from swapping the crystal for a 16Mhz/8Mhz speed up. The first version had bugs, and the third version was for the 8Mhz machines. ( still a few bugs ). This is the AT/370: https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compatible_systems https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compati... https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro-370/ https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro... https://anycpu.org/forum/viewtopic.php?f=22&t=350 https://anycpu.org/forum/viewtopic.php?f=22&t=350 There was one additional model of the IBM AT: THE IBM XT/286: An AT class mother board in an XT sized case. https://www.dosdays.co.uk/computers/IBM%20PC-XT-286%20(5162)/ibm5162.php https://www.dosdays.co.uk/computers/IBM%20PC-XT-286%20(5162)...
drfuchs 1y ago
Oops. Anyway, I remember attending a talk by one of the IBM engineers back when they first released the XT/370. He said that they looked at all possible ways to integrate their production line as a kind of secondary track off of one of the main production lines for the PC/XT, but the most economical option ended up being a separate facility that would receive normal pallets of regularly boxed, end-user XTs from the main factory, unbox them, make the mods, and pack them back into XT/370-labeled boxes for shipping.
kjs3 1y ago
Plenty of people remember, and used, them. Just not people who tend to hang out here. I knew several IBM VM dev types who had them as light dev/remote mainframe access machines, usually at home. They were popular enough there was a followon product: the PC/390 which was the same idea, more advanced processor, based on a PS/2 microchannel platform (and, AFAIK, OS/2). You want really obscure? Unisys had the same idea with the "Micro-A", which was a PC running OS/2 with a coprocessor card with a single chip implementation of an A-series mainframe. I know of 2, possibly 3, still around.

eek2121 1y ago

Back when I was a teenager, I would have absolutely gone down a rabbit hole like the author did. From "Upgrading and Repairing PCs" to reading all the technical manuals, usenet, etc. I definitely nerded out over this stuff! Glad to see folks still take an interest. These days, I've an acquired brain injury. Between that an old age, it was a bit hard to read, but also, just a little bit familiar, so I enjoyed it. Now I am expecting "256 color VGA programming in C" to resurface at some point! :D Old hardware was always so much fun...

mrandish 1y ago
256 colors? VGA? Bah! You kids with your newfangled graphics modes. 320 x 200 CGA and 16 colors is more than enough. See the linked "8088 MPH" video for proof: https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-all-your-emulators/ https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-al...
- m463 1y ago
  > 320 x 200 CGA with the opposite of smooth scrolling - video off during text scrolling. BLINK! kind of like the crazy blinking ancestor of vsync off
- vardump 1y ago
  320 x 200 CGA allows you to have only 4 colors at a time. Of course you can change the fixed palette on a certain scanline to have more colors. See for example California Games.
  - 1313ed01 1y ago
    160x100 CGA low resolution could do 16 color (bit of a hack, but semi-official). And then there were tricks to get more colors in higher resolutions as well, especially if you used the TV output instead of a CGA monitor. https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-illustrated/ https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...

sema4hacker 1y ago

My OCD tendencies would have made me label the one chip ..ODD.. instead of .ODD... just for a little more symmetry.

notherhack 1y ago

The blog refuses connections from VPNs. https://archive.is/Ef75R https://archive.is/Ef75R

viler 1y ago
Strange... if it does, that's not my doing - it seems to work fine with the VPN I use, but I'll look into it. Thanks for the heads up.

breakingcups 1y ago

I love this sort of digital archeology