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IBM 5150  -  BIOS Revisions


There were 3 revisions of the BIOS, differentiated by date (there are no version numbers).
The date format used is MM/DD/YY.

On the 5150 motherboard, the ROM in socket U33 contains the BIOS.
Note that the ROM's in sockets U29/U30/U31/U32 are not part of the BIOS.  Those ROM's contain cassette BASIC.

The photos below are merely representative.

If required, see here for information on substitution/replacement.

	Dated  04/24/81 Has the IBM part number of "5700051" printed on it. Useable only on motherboards of type 16KB-64KB Limitation #1:  By design, only recognises up to 544 KB of RAM. Limitation #2:  The BIOS expansion ROM in cards that have one is not recognised. Examples: EGA/VGA cards, hard disk controllers. (photo source: Framer at the VCFF))
	Dated  10/19/81 Has the IBM part number of "5700671" printed on it. Useable only on motherboards of type 16KB-64KB Has the same two limitations as the earlier BIOS.
	Dated  08/16/82 Has the IBM part number of "5000024" printed on it. May not have been publically released due to the bug described below.  Click here for information about a discovery 'in the wild.' BUG:  EGA, and 5150 compatible VGA cards, do not work if the video switches in motherboard SW1 are set to ON-ON  (but will if the switches are OFF-OFF). FYI:  The IBM 5160 also has an 08/16/82 dated BIOS revision. (Which does not have the same bug.) (photo source: compaqportableplus at the VCFF))
	Dated  10/27/82 Has the IBM part number of "1501476" printed on it. Useable on motherboards of types 16KB-64KB and 64KB-256KB The two limitations of the 1981 dated BIOS' are removed. This BIOS has bugs that require all 4 banks of motherboard RAM be populated and used. If you are upgrading a 16KB-64KB motherboard to this 10/27/82 BIOS, then read here. Some of these have content that starts with "1501476 COPR. IBM 1981" and others, "1501476 COPR. IBM 1982".  They are functionally the same.