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

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...

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mrandish 7 hours ago | parent [-]

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-al...

	▲	m463 7 hours ago \| parent [-]
		> 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

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notherhack 2 hours ago | parent | prev | next [-]

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

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drfuchs 8 hours ago | parent | prev | next [-]

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

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viler 8 hours ago | parent | next [-]

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.

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m463 7 hours ago | parent | prev | next [-]

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 3 hours ago \| parent [-]
		3 cards. CPU/Memory and communications cards.

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TMWNN 7 hours ago | parent | prev | next [-]

Article discusses and dismisses that possibility

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ForOldHack 3 hours ago | parent | prev [-]

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-compati...

https://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro...

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)...

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sema4hacker 6 hours ago | parent | prev | next [-]

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

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mrlonglong 9 hours ago | parent | prev [-]

Excellent write-up.

	▲	viler 9 hours ago \| parent [-]
		Appreciated, thanks!