Non-Parity vs. Parity

Parity     As data moves through your computer (e.g. from the Central Processing Units to the main Memory), the possibility of errors can occur . . . particularly in older 386 & 486 machines. Error detection was developed to notify the user of any data errors. By adding a single bit to each byte of data, this bit is responsible for checking the integrity of the other 8 bits while the byte is moved or stored. Once a single-bit error is detected, the user receives an error notification; however, parity checking only notifies, and does not correct a failed data bit. If your SIMM module has 3, 6, 9, 12, 18, or 36 chips then it is more than likely Parity. Logic Parity      Also known as Parity Generators, or Fake-Parity, these modules were produced by some manufacturers as a less expensive alternative to True-Parity. Fake-parity modules "fool" your system into thinking that parity checking is being done. This is accomplished by sending the parity signal that the machine looks for, rather than using an actual parity bit. In a module using Fake-Parity, you will NOT be notified of a Memory error, because it is really not being checked. The result of these undetected errors can be corrupted files, wrong calculations, and even corruption of your hard disk. If you need Quality modules be cautious of suppliers with bargain prices; they may be substituting useless Fake-Parity. Non-Parity      These modules are just like Parity modules without the extra chips. There are no Parity chips in Apple® Computers, later 486, and most Pentium® class systems. The reason for this is simply because Memory errors are rare, and a single bit error will most likely be harmless. If your SIMM module has 2, 4, 8, 16, or 32 chips, then it is more than likely Non-Parity. Always match the new Memory with what is already in your system. To determine if your system requires parity, count the number of small, black, Integrated Circuit chips on one of your modules.

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Last Update: 10:36 PM 6/29/01