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

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.

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.

Article discusses and dismisses that possibility

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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