I'm currently using a 667mhz ddr2 1GB ram in the DIMM1 slot. My motherboard supports up to 4GB 800mhz ddr2 ram so I'm planning to get 2gb 800mhz ddr2 ram to upgrade my system. I'm just wondering if it would make any difference to my system's performance which DIMM slot I put the ram into, as it is running at a faster speed and has more memory then the other ram. My motherboard has 4 DIMM slots btw.
All of the RAM modules will be automatically downclocked to the speed of the lowest speed RAM module installed.
In your case it doesn't matter which slots you have the RAM installed into since you will still be operating in single channel mode because of the memory module size mismatch. If your new memory module was a 1GB module then it would matter which memory slot you placed it into because then you could run in dual channel mode to gain better memory performance. Of course I'm assuming your motherboard supports dual channel operation.