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IBM 5150  -  Motherboard Versions


Photos of some IBM 5150 motherboards are at here.

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

IBM differentiated them by the amount of RAM that it was possible to fit into the motherboard's RAM sockets:
   • 16KB-64KB
   • 64KB-256KB

Both were not released simultaneously.  The 16KB-64KB motherboard was supplied in early model 5150's, and the 64KB-256KB motherboard was supplied in later model 5150's.

It is beyond the scope of this web page to discuss/document what some people may call sub-versions.  For example (one example of many), the two different ways that delay TD2 was implemented in the 64KB-256KB motherboard.


Example marking Motherboard RAM     Comments
5150_label_16kb_64kb_cpu.jpg  4 banks of 16 KB  • "16KB-64KB CPU" is printed on the motherboard.
 
 • Detail on the RAM for this motherboard is here.
 
 • As supplied, fitted with either the 04/24/81 or 10/19/81 revision of BIOS.
 • It was common for owners to upgrade the BIOS to the 10/27/82 revision via a BIOS upgrade kit.  See note 1.
5150_label_64kb_256kb_cpu.jpg  4 banks of 64 KB  • "64KB-256KB CPU" is printed on the motherboard.
 
 • Detail on the RAM for this motherboard is here.
 
 • As supplied, fitted with the 10/27/82 revision of BIOS.  See note 1.





Note 1 Due to software bugs, the 10/27/82 revision of motherboard BIOS requires that all four RAM banks be populated (and motherboard switch blocks SW1 and SW2 be set appropriately).
Additional information about that is at here.