PC Switch Settings  (includes PC-1 and PC-2)

DIP switches on the PC and XT tell the BIOS what equipment and how much
memory is installed.  These switches are read during the POST and bit
flags are set into the BIOS Equipment List variable and are made available
to the programmer via INT 11H (Equipment Check).

The topics above show details of the DIP switch settings, as well as
jumpers and other hardware configuration for the different standard IBM

Non-IBM PCs usually don't adhere to these settings.  For instance, Compaq
Portable switches bear no resemblance to those of the standard PC and
aren't documented in any manual available to Compaq owners.  Deskpro
switches are labeled inside the chassis.

See Also: POST
INT 11H (get equipment list)
INT 15H (extended AT services)
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Switch Settings