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The 640 MEG Shareware Studio 2
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The 640 Meg Shareware Studio CD-ROM Volume II (Data Express)(1993).ISO
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TIPS-069.ASC
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1992-07-16
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TIP #: 069
KEYWORDS: Memory, Parity Failure
UPDATED: May, 1992
PROBLEM: Computer reports "+++ ERROR: Memory parity failure! +++".
Replacing the bank of memory containing the error address reported
by the register dump does not solve the problem.
SYMPTOMS: This error message appeared on a Zenith 386/25MHZ computer system
with 8 Megabytes of memory installed. The problem was
intermittent, initially occurring only after the computer was used
for a long period of time. Further analysis showed that the length
of time was not as significant as the size of the programs being
used. Memory hungry programs like Lotus 1-2-3 generated the error
consistently. The address given for the error indicated that the
problem was in the first megabyte of memory, but replacing that
bank of memory did not solve the problem.
SOLUTION: Perform diagnostics without a memory manager (such as QEMM or
386MAX) installed. Memory managers may disguise the true address
of the parity error by converting Extended memory to Expanded
memory, which has no physical address. Some memory managers also
"sort" memory by speed, hiding the actual address. By running
diagnostics without a memory manager, the true address of the
offending memory chip may be accurately determined.
The problem with this machine turned out to be in the third bank of
memory. Programs that made extensive use of the EMS cache memory
would trigger the parity error. Since EMS memory was being
supplied by the memory manager, and paged in and out through the
page frame, the error location reported by the register dump was
inaccurate.
In this particular case, the error was also intermittent, making
diagnosis more difficult. To increase the chances of finding the
defective SIMM, I blocked the ventilation holes to increase the
temperature within the case while running the diagnostics program.
This caused the error to appear almost immediately when the test
reached the defective memory area. Replacing the defective SIMM
solved the problem, and the machine has worked flawlessly since
that time.