What is ECC?
ECC memory stands for Error Checking and Correction. Using ECC memory allows the system to detect and correct single bit errors. ECC is not recommended for home PCs because the home PCs are normally shut down regularly. ECC memory is most commonly found in servers where they are not shut down. It is estimated that a single bit soft error occurs once per 1GB of memory per month, running at 24 hours a day.
Flavors of ECC memory
Registered ECC uses buffers to temporarily hold data for one clock cycle before it is transferred. This increases reliability but sacrifices speed due to the additional clock cycle. We suggest Registered ECC for systems with 4GB of memory or more.
Unbuffered ECC allows the system to directly access the each memory chip on the module. It is faster but suffers a bit on the reliability side compared to registered ECC. Best used for system memory that is lower than 4GB.
You also see CL7 or CL9 on some memory modules like Kingston. These refer to the clock cycle. CL7 is faster than CL9 and is more expensive. Also, when a price list refers to kit of 2, it means that you get two pieces. So a 4gb in kit of 2 means that you are getting 2 pcs of 2gb that gives you a total of 4gb. Kingston does this to make sure that your memory modules are an exact match when you place it on your system