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| Troubleshooting the System Memory | Parity
I am receiving a parity error as soon as I boot up the PC
Explanation: A parity error is
occurring on a PC as it boots up. The parity error will typically occur as soon as the
system completes the power-on self test; the memory count that is performed will typically
pass without any problems being recognized. In some cases, when booting up Windows 95 or
Windows NT for example, the parity error will not appear until the graphical user
interface of the Windows operating system itself comes up on the screen.
Diagnosis: The most common cause of parity errors when first booting up the PC are
incorrect configuration or using the wrong type of memory. It is unusual for an actual
memory failure, of the type that parity checks for (meaning, you wrote one value into
memory and read back another value with a bit changed) to be encountered at the start of
booting, although it is possible.
Recommendation: Look on the screen to see if the system is giving you any sort of
memory address that indicates where the parity error is occurring. Reboot the system and
see if the same address comes up again, and then reboot a third time. Take note of whether
or not the memory location changes, and then continue below:
- If the parity error is coming up as soon as the BIOS tries to boot, and especially if it
fails at memory address "0000" consistently, this is a dead giveaway of trying
to use non-parity memory in a parity system. Make sure that you have used real parity memory if you have parity
- If you are or were running with parity checking disabled, double-check the BIOS setting
to make sure that it is still set as disabled. If it is enabled accidentally, parity
errors will result.
- I have encountered a defect in the Abit IT5H motherboard, version 1.5, which will cause
it to fail when using parity memory--it just does not work in this board due to a design
flaw. Every time parity is enabled a parity error is generated immediately at boot time.
It is possible that other motherboards may have similar problems. The only solution is to
replace the motherboard or run with parity checking disabled.
- If you are trying to run with ECC enabled
on a motherboard that supports both parity and ECC, change the ECC/parity BIOS setting to
straight parity and try to reboot. If the parity error goes away, and returns when ECC is
re-enabled, the chances are high that you have false
parity memory in your PC. False or "logic" parity memory is designed to fool
the standard motherboard parity circuits but will not work if you set the machine to run
with ECC. The only good solution is to replace the memory.
- Make sure that the modules you are using are appropriate for your board. In particular,
there are some motherboards that will not support the newer ECC-only modules. See this section for more in the
- On a new PC, it is possible that you have an actual hardware failure. If the parity
error address remains the same or is in the same general vicinity each time it is
encountered, this implies a failure of the memory itself. Troubleshoot
the memory itself here.
- Look in the section on parity errors encountered
during operation. It is possible that one of the causes there could be responsible for
a parity error encountered during the boot (just less likely than the causes listed
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