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IBM 5150  -  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:
   • 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.


Example marking Motherboard RAM     Comments
5150_label_16kb_64kb_cpu.jpg  4 banks of 16 KB  • 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  • 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.