ddr2 memory, 400 cl3 vs 533 cl4 vs 667 cl5 doesnt matter.

[hans007]

so i have about 4 gb or cl3 dd2-400 ram coming in and was thinking, 800mhz bus p4 is 64bit. thats 6.4 gbps. currently i have 1 gb of ddr2-533. and was thinking about if i should just use like 2 gb of ddr2 400 instead (4x512)

dual ddr2 (which is 128bits wide) 400 is 6.4 gbps
dual ddr2 533 is 8.0 gbps
dual ddr2 667 is 10.6 gbps

so bandwidth wise, a p4 can only use ddr2 400 anyway.

so i was thinking in terms of latency.

1/400mhz = 2.5 ns per cycle
1/533mhz = 1.87 ns per cycle
1/667mhz = 1.5 ns per cycle

so that means total latency for

400mhz cl3, is 7.5ns
533mhz cl4, is 7.5ns
667mhz cl5, is 7.5ns

so there is no difference in latency between all the flavors of cheap ddr2 even though ddr2 667 cl5 costs a lot more than ddr2400 cl3 (i can get twice as much ddr2-400 as ddr2-667 with same $). and i was thinking ddr2 -400 would be synchronous and 533 is not unless you have extreme editions with 1066bus. im sort of thinking that marketing and random uninformedness is causing us all to pay more for ddr2 ram that we dont need to be paying for 0 performance.

so i guess the only real reason to get say 533 , 667 or 800mhz ddr2 is because with less cycles of latency, you get a lower total latency , so theoretical 667mhz cl3 would be 4.5ns total latency, and 800mhz cl4 would be like having cl2 400mhz or 5ns

anyway, i dont have all these types of ram so this is just an idea more than anything. anyone have any comments?

 

[Slacker]

All that stuff you posted.... went right over my head

I just have a simple question, what DDR2 do I need for an Intel D945PSN board with an 820D chip, I have no clue, I have not built a system in a few years and it looks like they made it complicated to get the right stuff

 

[hans007]

i think ddr2-3200 cl3 would be more or less good as anything else you can get.

the only thing that would really beat it is cl4 667 or cl4 800 and well that would be not worth the money . i have an 820 also with a d945gcz btx board. so more or less the same setup except btx.

 

[Slacker]

O.k., I read through it all again, I get some of it, enough to understand that the different specs are more important in terms of synchronous timings than latency or bandwidth.

My chip is an 800mhz bus so ddr2 400 would be synchronous, and cheaper! :thumbsup: Thanks.

One more thing, it seems like I would want to fill all four slots or does that not really matter? if I plan on getting 2gigs should I get 512x4 or 1024x2?

Crucial has this..
DDR2 PC2-3200 ? CL=3 ? UNBUFFERED ? NON-ECC ? DDR2-400 ? 1.8V ? 128Meg x 64
2gb for $215.00 for 2 one gig sticks, it would be $5.00 more to get the same memory in four 512mb sticks.