RAM Parity - Memory Errors

Memory Errors

In earlier times faulty memory was relatively common, and parity errors, very noticeable to the user, not infrequent. Since then errors have become less visible as simple parity RAM has fallen out of use; either they are invisible as they are not detected, or they are corrected invisibly with ECC RAM. Modern RAM is believed, with much justification, to be reliable, and error-detecting RAM has largely fallen out of use for non-critical applications. Most machines in the twentyfirst century do not support parity or ECC, with consequent risk of data corruption; this has become acceptable as a consequence of the increased reliability of memory. Some machines that support parity or ECC allow checking to be enabled or disabled in the BIOS, permitting cheaper non-parity RAM to be used. If parity RAM is used the chipset will usually use it to implement error correction, rather than halting the machine on a single-bit parity error.

However, as discussed in the article on ECC memory, errors, while not everyday events, are not negligibly infrequent. Even in the absence of manufacturing defects, naturally occurring radiation causes random errors; tests on Google's very many servers found that memory errors were not rare events, and that the incidence of memory errors and the range of error rates across different DIMMs were much higher than previously reported.