Can I add a 2*2Gb pair to my 2*1Gb pair?

[Runbalk]

I always hear about how important it is to ensure memory modules match so was wondering just how closely they do have to match.

Currently I have 2Gb (2*1Gb) of ddr2 pc2-6400 RAM with the following timings: 800MHz, 4-4-4-12 2T @ 2.1V (EPP). I have 2 slots free that I want to put more memory in.

I was wondering if it was okay to get a 2*2Gb pair but with the same timings or if the module sizes had to be the same too?

 

[Runbalk]

Cool cheers. Well the only reason for adding an extra 4gb was just because I could. Is there not much of an advantage of 6 over 4? Mainly play computer games, but also do some video editing and 3d work every now and then...