What is the difference between ECC and non-ECC (non-parity) memory? Is there a performance difference?
ECC stands for Error Correction Code. It is similar to Parity, but more advanced. It can detect multiple errors in data returned from memory and actually correct a single error. ECC memory has 8 extra bits to support the ECC. The system board to be used must support ECC, and all of the memory in the system must be ECC for it to be actively supported. Your system board specifications will tell you whether or not you can use ECC.
Using ECC decreases your PC's performance by about 2%. Current technology DRAM is very stable and memory errors are rare, so unless you have a need for ECC, you are better served with non-parity SDRAM. Most importantly, ECC memory is only needed in mission critical enviornments like a web server. It serves little to no benefit for the average user.
If you already have a PC, you need to match the type of memory already installed in your system. If you are unsure whether you have ECC or non-parity, count the number of small, black, IC chips mounted on one of your existing sticks of memory. If the number of chips on one side is even, as in 4 or 8, you have non-ECC. If the number of chips on one side is NOT even, as in 9, you have ECC.
In short...
If you are building a PC and plan to use your system as a server or a similar mission critical type machine, it is to your advantage to use ECC. If you plan to use your PC for regular home, office, or gaming applications, you are better off with non-parity.