To ECC or not ECC

Greetings Several hours of reading the web and I still cannot overcome my density. I'm looking at a Socket 939 motherboard with one single-core Opteron 148. The motherboard supports ECC or non-ECC RAM The BIOS can turn off ECC if the RAM supports it. What is the kernel's involvement with ECC when it's enabled in the BIOS? Just reporting errors? Does ECC RAM incur a performance hit when no errors are detected? TIA & Cheers