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)...