DDR SDRAM Specifications - DDR SDRAM

flora

I am looking at buying a new Abit board that supports DDR SDRAM, but I am not sure about a couple of things.

1.) Is there really a need for ECC? If so, when?
2.) The board specs said that it could hold 2 non-buffered DDR chips or 4 buffered DDR chips. How do you tell if a chip is buffered?

I have looked around and haven't found anything to answer my questions. Below is the exact wording from the Abit board's specifications:

"Note: the motherboard accepts either up to 2 DIMMs of unbuffered DDR SDRAM (2GB max) or up to 4 DIMMs of registered DDR SDRAM (4GB max). You cannot mix unbuffered and registered SDRAM, nor can you have more than two sticks of unbuffered SDRAM."