AMD A64 Systems: RAM LATENCY VS RAM SPEED, which one is more important?

[amdguy]

I read tons of article and did extensive search on the board.
Some says with AMD the lower the latency the better, some say if you use higher speed RAM such as DDR 466 and 533, the higher bandwidth will offset the performance degradation causesd by higher latency.

SOME say for AMd it is best to use CL2 RAM and use higher MHZ RAM only if you OC the FSB. Now I am getting all confused here.

I am getting the MSI Nforce 3 250Gb mobo, what type of RAM should i get if I am doing OCing. Low latency DDR 400 or High bandwidth, high latency DDR 466 or 533?

 

[n0cmonkey]

Buy some of each and run benchmarks.

 

[chadomaly]

Originally posted by: n0cmonkey
Buy some of each and run benchmarks.

I hope the other 22,297 of your posts aren't that worthless and rude.

 

[n0cmonkey]

Originally posted by: crleap

Originally posted by: n0cmonkey
Buy some of each and run benchmarks.

I hope the other 22,297 of your posts aren't that worthless and rude.

Heh.

 

[amdguy]

help!!

 

[magomago]

I think ram latency is more important. someone was asking the same question (do a search) on whether they should keep their pc2700 ram or move up toe 3200 because they had 1 gig of pc2700 and they found some benchies where the A64 was 5% slower with pc2700; and to me it isn't worth it to pay extra.

But remember, for the pentioum4 it does matter a lot more~


Here:

http://forums.anandtech.com/messageview.cfm?catid=27&threadid=1338053&highlight_key=y&keyword1=a64


Found the threat for ya using the search of "a64"

 

[nycxandy]

Ram Speed... go read Anand's memory article with the OCZ 3700EB.

 

[DerwenArtos12]

yeah the speed is definatly better but only if you are going to use it well. get some good 4000 and run it in synch with your cpu, the a64's can do it and that will be so fast it will make your head spin,

 

[dguy6789]

the amd64 has a built in memory controller, so the latency on the memory itself means almost nothing in performance. you wont get even 5% more performance going from 4 4 4 15 to 2 2 2 6 memory. Get a higher mhz one, with amd 64, the latency does not matter performance wise.however, If it is a pentium 4, you need both.

 

[amdguy]

so if i get the OCZ DDR 550 RAM, I havel lots of headroom for overclocking and messing with the FSB right?

Please enlighten me as i am very new to the overclocking arena as I've been using Compaq computers for too long haha

 

[VirtualLarry]

Originally posted by: dguy6789
the amd64 has a built in memory controller, so the latency on the memory itself means almost nothing in performance. you wont get even 5% more performance going from 4 4 4 15 to 2 2 2 6 memory. Get a higher mhz one, with amd 64, the latency does not matter performance wise.however, If it is a pentium 4, you need both.

I disagree. The whole *point* of putting the memory-controller on-die on the A64 CPUs, was to reduce the latency to access main memory. I mean, the bandwidth of DDR400 is the same, whether on an AthlonXP system with a seperate chipset memory-controller, or an AMD64 with integrated memory controller. Yet, the AMD64 systems seem to score quite a bit higher, even on mostly memory-dependent benchmarks, AFAIK. Why? Lower latency. The fact that the pipeline on XP's and AMD64's is shorter than the P4 helps a lot with this equation too. On the P4, with its longer pipeline, and larger cache line sizes, latency is a little less important.

So I guess that, given equivalent overall bandwidth, lower latency is desirable, especially so with an AMD system. However, I'm not so sure of the answer, if the tradeoff were, say high-latency DDR500 vs. low-latency DDR400. For a P4 system, I would probably take the DDR500, but on an AMD64..? I haven't researched enough to say one way or another. But latency does matter, in fact with the integrated memory controller of the AMD64 I woulds say it matters more than in either an XP or P4 system.

Edit: After reading some of the responses in that other linked thread (several of which did seem to indicate expecting a significant performance difference from running lower-latency memory, along with a few that did not), I had realized that I neglected to account for the potential impact of the AMD64's prefetching mechanisms, to "hide" some memory-access latencies. So perhaps the issue isn't as significant as I had first thought, although my personal workload (a certain amount of compiling) does benefit from a shorter-pipeline CPU, and lower-latency memory. Offhand, I wonder if possibly that is why so many games seem to show better performance on an XP and even moreso an AMD64 system, due to the workload of most PC games favoring a shorter-pipeline CPU architecture as well.

 

[nycxandy]

Originally posted by: VirtualLarry

Originally posted by: dguy6789
the amd64 has a built in memory controller, so the latency on the memory itself means almost nothing in performance. you wont get even 5% more performance going from 4 4 4 15 to 2 2 2 6 memory. Get a higher mhz one, with amd 64, the latency does not matter performance wise.however, If it is a pentium 4, you need both.

I disagree. The whole *point* of putting the memory-controller on-die on the A64 CPUs, was to reduce the latency to access main memory. I mean, the bandwidth of DDR400 is the same, whether on an AthlonXP system with a seperate chipset memory-controller, or an AMD64 with integrated memory controller. Yet, the AMD64 systems seem to score quite a bit higher, even on mostly memory-dependent benchmarks, AFAIK. Why? Lower latency. The fact that the pipeline on XP's and AMD64's is shorter than the P4 helps a lot with this equation too. On the P4, with its longer pipeline, and larger cache line sizes, latency is a little less important.

So I guess that, given equivalent overall bandwidth, lower latency is desirable, especially so with an AMD system. However, I'm not so sure of the answer, if the tradeoff were, say high-latency DDR500 vs. low-latency DDR400. For a P4 system, I would probably take the DDR500, but on an AMD64..? I haven't researched enough to say one way or another. But latency does matter, in fact with the integrated memory controller of the AMD64 I woulds say it matters more than in either an XP or P4 system.

Yes, of course it matters.

And the high latency DDR500 will score better than low latency DDR400 on an AMD64.

 

[DerwenArtos12]

Ok, I will solve this quite simply, Anandtech's most recent memory testing. It is quite obvious that the higher speed performs better.

 

[imported_nitrus]

Another simple solution, if you have the cash get the new corsair 3200xl's (about 325 for a gb). you can run ddr400 dual channel @ 2-2-2-5, ddr466 dual channel @ 2.5-3-3-7, or ddr500+ single channel @ 2.5-3-3-7. they reviewed the "pro" series ram with the LEDs witch is why i think they couldent get past 466 in dual channel in the review. The ram is manufactured by samsung and is rated @ DDR500 on the IC level.

rojack 3200xl review

anandtech 3200xl review

3200xl pricing