Hardware Reference
In-Depth Information
1 = Error occurred on the motherboard.
2 = Error occurred in an expansion slot.
In this example,
yyyyy
represents a number from 00000 through FFFFF that indicates, in
hexadecimal notation, the byte in which the error has occurred.
Also, (z) is (S) or (E):
(S) = Parity error occurred in the system unit.
(E) = Parity error occurred in an optional expansion chassis.
Note
An expansion chassis was an option IBM sold for the original PC and XT systems to add
more expansion slots.
When a parity-check error is detected, the motherboard parity-checking circuits generate
a nonmaskable interrupt (NMI), which halts processing and diverts the system's attention
to the error. The NMI causes a routine in the ROM to be executed. On some older IBM
systems, the ROM parity-check routine halts the CPU. In such a case, the system locks
up, and you must perform a hardware reset or a power-off/power-on cycle to restart the
system. Unfortunately, all unsaved work is lost in the process.
Most systems do not halt the CPU when a parity error is detected; instead, they offer you
the choice of rebooting the system or continuing as though nothing happened. Addition-
ally, these systems might display the parity error message in a different format from IBM,
although the information presented is basically the same. For example, most systems with
a Phoenix BIOS display one of these messages:
Memory parity interrupt at xxxx:xxxx
Type (S)hut off NMI, Type (R)eboot, other keys to continue
or
I/O card parity interrupt at xxxx:xxxx
Type (S)hut off NMI, Type (R)eboot, other keys to continue
Thefirstofthesetwomessages indicates amotherboardparityerror(ParityCheck1),and
the second indicates an expansion-slot parity error (Parity Check 2). Notice that the ad-
dressgivenintheform
xxxx:xxxx
forthememoryerrorisina
segment:offset
formrather
thanastraightlinearaddress,suchaswithIBM'serrormessages.The
segment:offset
ad-
dress form still gives you the location of the error to a resolution of a single byte.
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