PC2-5300u = non-ECC, unbuffered
PC2-5300e = ECC
PC2-5300p = Parity
PCs-5300r = Registered
PC2-5300f = Fully Buffered
Parity just checks for errors and finds them – 1 extra bit
ECC attempts to repair the errors as well – 8 extra bits
Parity uses a checksum to make sure the data in memory is not corrupted, if it is it cannot fix it. ECC employs a RAID 5 like philosiphy. Even if there is a certain level of corruption, it is possible to fix it.