The relation between Ram and Processor

[vitinho]

A processor (Intel) with 400 MHz FSB should be matched with what speed of ram? 266, 333 or 400 DDR? Why? Any one can explain? And how about if it's an AMD processor? Thank you!

 

[Duvie]

A 400mhz intel cpu produces 3.2gb/s of theoretical bandwidth and therefore dual pc1600 or 200mhz ddr would be optimal for it. The pc 1600 stands for 1600mb or 1.6gb/s or bandwidth and then times the 2 channels and you have 3.2gb/s...

the relationship is the cpu can only handle that much throughput so anymore is a waste and any less like scddr of even pc2700 or 333mhz ddr in underkill....

Theoretically I guiess one can state that in single channel mode one stick of pc3200 or 400ddr is also equivalent to that of the 400mhz p4. However the 400mhz fsb is quad pumped 100fsb and tring to find any intel chipset with 1:2 ratios in a scddr mode will be tough to impossible.


table:

p4 400fsb = (2) pc1600 200mhz ddr sticks = (1) pc3200 400mhz stick

p4 533fsb = (2) pc2100 266mhz ddr sticks

p4 666fsb = (2) pc 2700 333mhz ddr sticks

p4 800fsb = (2) pc 3200 400mhz ddr sticks


You see the pattern??? p4 800fsb = 2stciks or 2 x 400mhz for 800...800 = 800


Ofcourse cas setting will effect actual memory bandwidth as well as in most instance a pc3200 stick ran at 400mhz will not yield 3200 in say sissoft sandra instaed will be around 3000 only...

 

[vitinho]

All understood, Duvie... Gracias
But how about if I use 2 sticks of DDR 400 instead of one... what advantages do I get?

 

[Duvie]

JUst enough to actually get to 3.2gb/s of memory bandwidth. Like I said the theoretical of pc3200 1 stick would be 3.2gb/s but do to timings and whatever quirks it often does not do that. The 2nd stick would insure you peg the max bandwidth allowed by the 400fsb p4. Not much advantage but in the future you may step up to a 533fsb or 800fsb chip and have room to grow into it.

It is like amd when ppl started running 400ddr with a 333fsb xp chip (before 400fsb bartons) The advantageous were 1% or less in a lt of test (neglible) In that case pc2700 or 333mhz ddr was a perfect fit for the cpu's 2.7gb/s of bandwidth. The only increase was likely due to once agai pc2700 often only scores in the 2500's in bandwidth test so it was not a 100% max out.


I would recommend ocing the chips fsb ,aybe upwards towards 133fsb...I had a p4 1.6a (400fsb) chip that did 171fsb. If you can get the fsb up any you will take advantage of the memory you have...

 

[vitinho]

well, my mobo only supports DDR 333... but unoficcialy DDR 400 supported...
how about if I get a stick of 512 DDR 400, instead of 2 256 DDR 400... (my mobo is single channel, not dual)
and the CAS latency thing, how & how much should I tune it to?

 

[WaTaGuMp]

Originally posted by: vitinho
well, my mobo only supports DDR 333... but unoficcialy DDR 400 supported...
how about if I get a stick of 512 DDR 400, instead of 2 256 DDR 400... (my mobo is single channel, not dual)
and the CAS latency thing, how & how much should I tune it to?

The latencies you want to set are the lowest you can get and be stable, if you can run 2 2 2 5 then do so if not then relax them try 2.5 2 2 5 or 2 3 3 6 etc etc. Uping the dram voltage can help with latencies so play around with that also, 2.8 2.85 are normal for alot of memory now a days.

No reason to get 2 sticks if your running single channel unless you need 1 gig then 2 sticks is ok.