I want to buy 3 X 4 GB DDR3 1600Mhz Ram, I already have 3 X 1GB DDR3 1333.Can i put the memory in and will it work IE. can it downlclock the 1600Mhz to 1333Mhz. I cant over clock my Core i7 Motherboard because it does not support overclocking (Pegatron IPMTB-GS).
More about :memory speeds motherboard compatibility
RAM does not run at a "certain speed". Rams runs at the speed the motherboard configures it to run at by default.
1600mhz RAM means that it is guaranteed to work at speeds up to 1600mhz, but it will work perfectly fine at ANY speed below that.