View Full Version : Ibm Pc Rom Bios

Great Hierophant
October 4th, 2006, 07:19 PM
The IBM PC 5150 had three BIOS revisions:

All BIOSes are 8KB. The third is vastly more common than the earlier revisions. All

The IBM PC/XT 5160 had three BIOS revisions:

The first BIOS is 8KB and probably virtually identical to the PC's 10/27/82 BIOS. The second and third BIOS are 32KB and are similar to the AT BIOS. I don't know whether you could use a second or third BIOS in a 64-256KB motherboard because the ROM socket could be looking for an 8KB ROM. Alternately, the BIOS ROM in the XT could be a 32KB chip with only 8KB used.

The IBM PC AT 5170 had three BIOS revisions:


In this case, each BIOS is 32KB, but the first BIOS is tied to the earlier motherboards with the piggybacked RAM. The second BIOS is useable in these motherboards because IBM supplied a hard drive upgrade for the old ATs with ROMs containing the new BIOS and updated drive tables. The third BIOS is only found in ATs with the 8MHz 80286s and can't be used in PCs with 6Mhz 80286s.

The IBM PC/XT 286 had only one, as did the IBM PC Convertible 5140 and the IBM PCjr 4860. The IBM PC Portable 5155 uses the PC/XT first BIOS.

Dumps are available for each of the last BIOSes of the PC, XT and AT, but the others could be useful as well. Anyone care to dump those, its really easy to do.

October 4th, 2006, 08:16 PM
Sorry .. part of this is wrong. Including BASIC (which is part of the ROM), the BIOS size on the PC and XT is 40KB, not 8KB.

My source is "Upgrading and Repairing PCs, 8th Edition".

Great Hierophant
October 4th, 2006, 08:44 PM
I didn't include the BASIC, which didn't change much, if at all within the six years of BIOS revisions. But you can add 32K for the total amount of ROM within each system.

October 5th, 2006, 02:16 AM
Alternately, the BIOS ROM in the XT could be a 32KB chip with only 8KB used.
For the first BIOS version, yes (if you exclude BASIC). Have a look at the '5160 BIOS versions' post in the '5150 vs. 5160 FAQ' thread.