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Introduction
Checkpoint codes or in short CP codes are two-digit hexadecimal numbers that
are outputted by the system unit during the startup to indicate which part of
the POST process is currently being executed. Should the system hang or
unexpectedly restart before finishing the POST process the CP codes can be used
as a troubleshooting aid (especially in cases where no error codes are
displayed).
All PS/2 machines output the CP codes to the primary parallel port. To read
them you will need either a separate hardware logic or another computer
(details HERE). Later PS/2 systems also display
the codes on the computer screen (typically in the bottom right corner),
however, this output method doesn't cover the early codes that precede the
initialization of the video subsystem. The Model 95 is an exception here - it
displays the CP codes on the Operator
Panel.
Checkpoint Lists
The meaning of the CP codes differs between the individual PS/2 generations:
Additionally the Type 4 (and Type 3) complexes output early
4-digit SDL Codes.
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