RAM - What is "ECC?"

Erm I've got another question.

KINGSTON 256MB PC-800 (400MHz DDR) - S$235
KINGSTON 256MB PC-800 (400MHz DDR) w/ECC - S$285
(Source - Hardware Zone)

What is "ECC?" Why is RAM more expensive with ECC?

ECC=Error Correcting Code, as the name implies if there is an error in the information on the RAM the system can fix that (without ECC the error would go unnoticed)

Though it requiers extra time and thus slows down your system, it is usually only supported on servers...

You will need to verify that your mobo really supports it if you indeed want ECC RAM...

In order to get ECC functionality, ALL of your RAM must be ECC.

To be honest, its not really something I would imagine that you might want unless you are running like a database server or domain controller or something. But if you buy high capacity RAM (i.e. 1 GB Dimm or something) you may find that it is only available in ECC because its thought that only servers would require such capacities at this time.