Microsoft KB Archive/68729

Meaning of Memory Parity Error Messages PSS ID Number: Q68729 Article last modified on 02-26-1992 PSS database name: W_Win3

3.00 3.00a

WINDOWS

Summary:

The syntax of a parity error message depends on the machine. The message can appear in a variety of forms, such as:


 * Memory Parity Error
 * Parity Check 2
 * Fatal Parity Error
 * MEMORY PARITY INTERRUPT AT 114F:006E

An intermittent error at boot up might read something like:

READ/WRITE FAILURE @ 2CD9F0 READ D2D3 EXPECTING D3D3

These are hardware error messages, indicating that a defective or damaged RAM memory chip has been addressed.

To test the RAM, run a recursive system diagnostics program on the computer, which will accurately check all the RAM memory addresses.

More Information:

When information is sent from the CPU to RAM, the number of bits must be an even number. The parity bit is set by the parity chip, so that an even number of bits are always being sent.

Data Bits Parity Bit ——— ———-

1 1 0 1 1 0 1 0 1 (parity bit set)

1 1 0 1 1 0 0 0 0 (no parity bit set)

When the information is read back from RAM to the CPU, the number of bits is checked by the parity chip. If the information was written to a bad chip, the bit’s value will change, causing the parity to change, and the parity chip to take notice.

The following is an example:

G = Good chip B = Defective chip

Memory Chips G G G B G G G G Parity Bit ———— - - - - - - - - ———-

CPU->RAM 1 1 1 1 1 0 0 0 1

RAM->CPU 1 1 1 0 1 0 0 0 1 /

Data Bit Changes

In the above example, the fourth data bit was changed in RAM (due to a faulty chip) and now the sum of the bits is odd. When this information is read back into the CPU, the parity chip notices this and sends a fatal trap error to the CPU, which generates the parity error message and locks the computer up, requiring a cold boot.

Reference(s):

“DOS Power Tools” Paul Somerson, 200-202, Bantom Computer Books, 1988.

Additional reference words: WIN30 3.00 3.0 3.00a 3.0a

Copyright Microsoft Corporation 1992.