Switches for original IBM PC's and XT's

If you have two DIP switch blocks and 5 slots, you have a PC. If you have one DIP switch block and 8 slots, you got an XT. Though most PC's were floppy based and most XT's were hard drive models, both were sold both ways and either may have had a hard drive added or removed over the years.

In historical order, first the PC, then the XT:


IBM PC

Switch block 1, near center of board:

Switch block 2, near power supply:

Switches 1, 2, 3, 4, 5 = Total memory installed


IBM XT

Switch block 1:

Note that many of these settings make more sense if you consider ON as a binary zero and off as a one. Since you must have at least 1 bank of memory, switches 3 & 4 ON,ON means binary 00 extra banks, or just one bank. off,off is binary 11, or 3 extra banks for a total of 4 banks.

Comments, corrections, clarifications welcome!


Paul Reid 71031.3603@compuserve.com
USED WITH PERMISSION FROM PAUL REID

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