How can I decide if a memory is good or bad?

[kpagcha]

I need to buy a new computer and as long as I know the most important things are CPU, GPU if you want to play games, and memory.

What should I be looking at in order to judge how good a memory is? I know not only its capacity, but also the model, meaning DDR3 is better and newer than DDR2.

I also know that different models work at a different frequency, and each motherboard support different range of frequencies. Does this impact on the performance?

I would like to get some tips in order to evaluate different memories.

 

[Alpha3031]

CAS Latency/frequency is the latency in ms, generally you'd want lower latency in ms and higher frequency. For capacity, you generally can't go wrong with a 2x4 kit.

 

[Tradesman1]

With most fairly modern systems look for 8GB and generally 1600/9 minimum (which is considered entry level today) in a 2x4GB to enable the extra performance from dual channel (up to 10-15%)...Yes will want DDR3...depending on what all you do or plan to do with the rig a higher freq may be better (faster) as gaming primarily just uses the DRAM as a data conduit