copied from a forum because i was looking for it as well a few weeks ago
Buffered means exactly that, there is a buffer in the ram to reduce the electrical load on a motherboard. This is typically found in server and high-end workstation boards. It adds a 1 cycle delay to memory reads.
Un-buffered means that the system reads more or less directly from the memory banks, its faster because it doesn't have to let the ram prep the information so to speak, but it has limits in the number of chips and the densities that can be used. It's common to see boards that support 1 or 1.5GB un-buffered 2 or 3 GB buffered (or the respective limits for the appropriate board) memory configurations.
Parity memory uses a parity bit in an attempt to insure data integrity. Again this is used in server and workstation level systems. Parity unlike ECC cannot correct errors, only alert the system that one has occurred.
I know you didn't ask, but ECC memory is similar to parity, but it uses its extra bit to not only check but can correct errors in memory reads. Because it's done by the chipset only, it cannot determine if the data was written correctly, only that what was read is correct to what is known. The amount of correction is typically a single bit, but that doesn't necessarily need to be the case. (Note: I have never seen an ECC system that could correct more than a single bit error.) ECC adds a significant penalty to read and write operations, so is typically used only in critical applications, hobbyists and tweakers are typically encouraged to disable ECC functions on their systems.
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