What is ECC and what does (un-)buffered/registered means?
ECC means Error Checking and Correcting. ECC is a code which is used to correct data errors and which is saved at the end of each sector. This error correction is generally used for servers and is utilized for all memory modules except for the EDO RAM memory module. For the R/DIMM memory modules this error correction is easy to recognize as 2-3 additional small chips are connected to the pins. The ECC error correction is compatible for all common RAM memory modules. This is not the case for (un-)buffered/registered RAM memory modules. This type of RAM memory module is not compatible to common R/DIMM memory modules without this feature or to main boards without corresponding support. The ECC error correction is no longer used as the modern RAM memory modules do not require this method of error correction any longer.