What are PCI parity errors?

Effectively, a PCI parity error occurs if a PCI transaction suffers corruption.

Parity data is generated on all PCI transactions.

From the PCI bus specification: "Parity generation is not optional; it must be done by all PCI-compliant devices."

Parity checking during data reads is also mandatory on all devices except those which will never be included in add-in cards (i.e. motherboard or chipset-integrated devices), and "temporary data" devices (e.g. graphics adaptors).

Many BIOSes do not enable PCI parity error checking (EDAC does).

Unreported PCI parity errors are very bad news for devices like PCI hard disk controllers.

You may well have experienced PCI parity errors in the past (it's just that your computer didn't tell you about it!).