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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting the System Memory | Parity Errors ]

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 checking enabled.
  • 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 differences.
  • 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 above).

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