Low speed ram for high speed FSB

[geckoracer]

I'm probably asking a nube question so please bare with me.

Why are all the high-end motherboards like EVGA 122-CK-NF68-A1 running a max of DDR2 800 on a 1333mhz bus; when they could run DDR2 1066? It's drastically closer to being at bus speed with minimal overclocking. It only makes sense to me that you want your RAM to run at the speed of your bus, or is that mistaken?

I realise they claim 1200mhz on SLI ready RAM, but I've read that its a gimmic. Though I haven't read a clear explanation why. Maybe someone can point me in the right direction on that too?

Thanks in advance for your words of wisdom!

 

[Peter]

Welcome!

Good question ... as long as you let yourself be confused by marketing numbers.

You got 128bit wide ("dual channel") DDR2-800, this is actually 400 MHz, two data bits per clock, 128 bits wide. FSB1333, which translates to 333 MHz, four data bits per clock, 64 bits wide, which is actually SLOWER than the available RAM throughput.

The perfect RAM speed for this CPU would let the northbridge run a synchronous 333 MHz bus clock, meaning that DDR2-667 would actually do the job.

The perfect solution would be to eliminate the FSB and run the RAM directly off the CPU. Oh look, AMD already did that in 2003.

 

[geckoracer]

"AIC" said the blind man. Thanks for the info! This helps me build my box with assurance. ^_^