What is the Difference between ECC memory and Non-ECC Memory and does it matter which type I buy as long as they are the same?

ECC memory has additional bits on the simm that can be used for either Parity Checking or automatic single bit error correcting by the system board. Old PC, 486 and before normally had Parity Checking. This is done by haveing 9 bits per byte instead of only the 8 bits required. With 64 bit wide memory simms it takes the same number of bits to do Parity Checking as ECC (which is better). Parity Checking just reports memory hardware errors (lost data bits) and allows the system code to abort the operation and stop the system with an error message. ECC on the other hand allows the system board to "correct" the error and keep running. Without either, a memory hardware error goes undetected until a program crashes, data files show up with strange errors or your system get corrupted. For Parity Checking or ECC to work, all memory simms in the system must be ECC type, and you must enable the feature in the system BIOS. However, there is no reason that ECC memory can not be used with non-ECC (standard memory) as standard memory. It is often made with better quality memory modules anyway. If they are the same price and quality, get the ECC memory. If you can replace all your memory with ECC simms, then turn on ECC checking for a more reliable system. I can never find ECC memory when doing a major upgrade.

hello thx jackg just learn something new. have a grate day OT Forum

There may be no reason why they won't work together but sometimes it won't anyway. Dell ECC memory leaps to mind as I have yet to find ANYTHING that will work in tandem with it. When it comes to a memory upgrade I have found it not so important the brand or type but rather that they are all identical.Get it all at once from the same place and it will most probable work where a mix n match may or may not. ECC is WAY to pricey and only realy intended for servers originally anyway. Jimi_l