[citation][nom]knowledge seeker[/nom]For DDR3 memory, should the memory speed be half the FSB frequency, as is the case for DDR2? I have seen many comments built around that premise, drawing the necessary conclusion that DDR3-1600 would require the impossible FSB of 3200 to be fully utilized. Therefore, buying such memory is useless. If that is the case, I would have thought that an article on "mainstream-ready" DDR3-1600 would have mentioned that fact. For the sake of clarity, could the author of this article please comment on this issue? Is there ANY rational reason for using DDR3 memory on an X48 motherboard?[/citation]
It used to make sense to run the memory and FSB at the same clock rate, back in the PC-133 days. Memory controller overhead back then would often make the system perform worse with the memory set to a faster speed. But memory controllers got better, and eventually speeds of up to 1.5x FSB clock showed small performance gains.
DDR3-1600 runs at 800 MHz, which is 1.5x 533. So, if your CPU was overclocked to 533 MHz FSB clock (FSB-2133), having DDR3-1600 would make sense already. And 533 MHz is pretty easy to do with many of today's chipsets.
When the next generation of Intel desktop processors are available in the near future, they will have the memory controller onboard with no FSB limitations on bandwidth. As with AMD's solution, gains from faster RAM will only be limitted by the processor's ability to use it.
And that's where motherboard manufacturers come in. Even though memory speed will be controlled at the processor, processor parameters will be controlled by BIOS. Everyone is talking about speeds as high as DDR3-2000 being available on some of the high-end boards.