IBM 5160  -  Motherboard Versions

According to IBM user documentation, there are 2 versions of the motherboard.

IBM differentiated them by the amount of RAM that it was possible to fit into the motherboard's RAM sockets:
   • 64-256KB
   • 256-640KB

Both were not released simultaneously.  The 64-256KB motherboard was supplied in early model 5160's, and the 256-640KB motherboard was supplied in later model 5160's.

Example marking Motherboard RAM     Comments
5160_label_64_256kb.jpg  4 banks of 64 KB  • Detail on the RAM for this motherboard is here.
 • Supplied with the 11/08/82 revision of BIOS.
 • This motherboard is also found in the IBM 5155.
 • A modification is possible so that 640K of RAM can be fitted on the motherboard.  See note 1.
5160_label_256_640kb.jpg 2 banks of 256 KB
2 banks of 64 KB
 • Detail on the RAM for this motherboard is here.
 • Supplied with either the 01/10/86 or 05/09/86 revision of BIOS.

Note 1 An IBM supported modification is possible that allows 640K of RAM to be fitted in the RAM sockets of the 64-256KB motherboard.
You will need certain parts.  The procedure can be found here.
Be sure to keep track of what you do, so that if things do not work out, you can undo what you have done.
If you are successful, consider marking the motherboard in some way to remind yourself (and others) that the motherboard has been modified.

Note that as the pointed-to procedure indicates, the jumpering of pins 1 and 2 on jumper pad E2 (photo), is the same as connecting pins 1 and 8 of U44 together via wire (photo).  Both achieve the desired outcome, which is the grounding of pin 1 of U44.  Your choice as which of those two methods you use.