this type of ram used a parity bit to be sure that it's data was valid- typically found in server class machines. i don't believe our macs even support this type of ram and i do know that when you do have a machine that supports it, all of it has to be ecc ram - you can't mix it. generally you only buy it when your required to, and it costs more. On Sunday, August 17, 2003, at 08:01 AM, mentholiptus wrote: > Can someone explain what "ECC" as opposed to "non-ECC" means when > purchasing memory? Will "non-ECC" memory work in a G4/G5?