I recently bought a custom PC on the cheap. It is an i5 750 2.8ghz in an Asus P7H55-M motherboard and with 1 x 2gb Corsair XMS3 1300. I decided this month to get a bit more memory and just wanted to upgrade to 4gb but couldn't find a way of only buying 1 x 2gb stick. So i bought a pair - Corsair XMS3 4GB (2 x 2GB) 240-Pin DDR3 1600. Can I slot these in with my other 2gb stick to make 6gb even though it is only dual channel or should I remove it and just run the new 4gb??
I did give it a go and it seems to run fine, I'm running Windows 7 64bit and it recognises the 6gb, just wanted to know whether i'm getting any added performance from it or whether it may cause instability??
Get the following specs for the 1300 dimm and the 1600 dimms:
Frequency (1300 and 1600, easy enough)
Timings (i.e. 8-8-8-18 and 9-9-9-20 or whatever).
Then, set your system to the lowest voltage, slowest frequency (here, 1300MHz, and higher timings (i.e. 9-9-9-20 or whatever they turn out to be).
By using the safest settings (lower voltage and speed, slower timings), you'll ensure that all the dimms run smoothly. You risk instability if you use timings that are too fast or if you run your 1300MHz dimm at 1600MHz speeds. You risk damage if you over-volt your memory, but usually you can undervolt a little with no stability problems (assuming you don't overclock the memory). I'm going to guess that both sets of memory run at the same voltage already, and you just need to adjust the frequency and timings (if not already auto-detected to the slower of the two).
To make sure its stable, you can run memtest86+ for a few hours (or overnight) to make sure it doesn't detect any errors.