Memory modules CL2/CL3... Most memory module beside the size and speed also have either a CL2 or a CL3,what?

Question

does this mean,,and r they interchangeable

Answer 1

CL is CAS latency or the time (in number of clock cycles) that elapses after the memory controller sends a request to read a memory location and before the data is sent to the module's output pins. The lower the number the better is the memory's performance. They are interchangeable but when you mix modules, BIOS would default CL setting to the higher number. Some more info here:
http://en.wikipedia.org/wiki/CAS_Latency