RAM compatibility

[Averyius]

I currently have two RAM DIMM - modules installed in my self-built computer, each DDR2, 512 MB, 667MHz, PC2-5300 from "Corsair". I want to buy extra RAM modules to improve performance. I have the possibility of buying some second hand RAM modules designated as 512MB GEIL PC2-4300 (DDR2-533) CL=3-3-3-8 (GX5124300UX) by the seller. He tells me it is not advisable to mix my ones with his ones but I get the impression he just wants to sell me the five pieces he has instead of just two more. He advertises with a price of €1 (per piece I assume) but wants € 19 for all five. I live in Austria incidentally and am using this forum since I am British and need an English language forum.
Can anyone tell me if my RAM modules are compatible with the ones he is selling? Is it ok to buy and install two extra but different RAM modules in the two empty DIMM slots even if they are DDR 2? Will the computer still work?

 

[txus.palacios]

It is not usually recommended since things can go south. Incompatibilities and such, so he was not scamming you. Although, if I have to be completely honest, I have mixmatched a lot of different modules, and as long as clocks, latencies and voltages are the same you shouldn't have a lot of problems.

 

[ATMINSIDE]

The computer will still work, but will potentially be unstable.

I would just get all the sticks from him personally, then replace your current RAM with the GEIL RAM. Especially since they run at two different speeds.

 

[txus.palacios]

He could always downclock the Corsairs.

 

[ATMINSIDE]

He could always downclock the Corsairs.

There's a guy in the AMD section right now that can't OC his CPU because of mismatched RAM. They also won't run at 1600 (which both sets are rated for), and are still unstable at 1333.