Memory Timings Analysis

keefe007 writes "It's generally known that smaller and more aggressive memory timings combined with higher clock speeds leads to higher performance, but for the most part, the increase in performance from tweaking each individual setting is relatively unknown. Perhaps in a bit too ambitious move, I set out to examine the impact of each individual memory timing and clock speed on overall performance. Find out the results of the tests at Techware Labs."

Comments

cas vs bus speed

[kochsr]

so what i got out of that is that increasing the speed of the memory (from 133 -> 166) is a much larger difference than bumping down the cas latency. i think i'd rather have memory on a faster bus than at a lower cas then.

but people will always say they have their stuff at the most agressive timings just to say that they are there, even though the average performance increase is only 0-2%

Re:cas vs bus speed

[photon317]

Yeah, that's a problem I have with this guy's test results. He's taken all the memory parameters which have very different purposes and effects, and rated them all on a scale of percentage increases in memory bandwidth.

The important effect of dropping CAS latency is that it improves memory response time on a small request - it's not meant to really give a big boost to bulk bandwidth.

You can think of the tradeoffs from spending a fixed dollar amount on clock speed boosts vs lowering CAS times as kinda like the difference between going RDRAM and going SDRAM. RDRAM had much higher bandwidth, but the latency sucked. SDRAM had lower bandwidth, but also had lower latency.

So wrap it up - this test is uninteresting because it rated all those parameters based on how they affected bandwidth, when really only the clock speed speed has a significant impact on bandwidth - a lot of the other parameters are really more about latency and responding well to certain patterns of access.

Results = Waste of Time?

[Baron_911]

Wow, considering all the settings that were tested, and the only improvment beyond 1% was the Clock Speed, seems like the rest of it was kinda a waste...

What beats me...

[jkrise]

Is the fact that accountants and finance managers (decision makers in PC buying deals) talk as if they understand all these things better than sysadmins. SDRAM, DDRRAM, RambusRAM, L2 cache, on-chip cache and all that marketing crap is heavily used by these decision makers.

Last year, I did a demo of a Via system with SDRAM and it did about 40% faster than a DDR-RAM board. The VP-Fin chap has become highly suspicious of any memory performance graphs or numbers, these days. And in true BOFH style, I've got decision-making rights on all PC purchases.

Thanks to all the confusion.

this guy

[daveatwork]

has was too much time on his hands. WAY too much time.

Speaking as an engineer, I do hate buying new stuff because its cheaper to do so rather than spending time tweaking the old stuff, but 100's of combinations, for a few % increase? Even I would be perfectly happy in paying the money rather than loosing 0.05% of my life!

Re:Sounds like an Ad...

[Lafe]

If Dell sent you, gratis, their high-end gaming machine for you to review and post about on your blog (assuming you have one), would you not mention the fact more than a couple of times in thanks for the free machine?

Sure it's advertising for whomever the vendor was, but its also a sponsorship of something that the author might have had to pay for himself. Or might have had to do without.

this is news?

[caino59]

seriously, for anyone that knows what they are messing with when changing these settings - don't you already know that it increases performance?

must be a slow day.

Other Benchmarks

[aliens]

Synthetic Sandra are nice, but I'd rather he ran 3dmark2001. It's what I would've done ::)

Testing method

[nuggz]

Someone needs to take a course, or read a book on Design of experiments.

Then he could have gotten the same information with many fewer test runs.
Also you could end up with interaction effects, which is nice. Maybe two settings have a greater or lesser effect.

except he fucked up.....

[oliverthered]

1: he didn't disable system cache, this could have cause the >theoretical performance increase.

2: In his final analysis he failed to mention that there must be another bottleneck in the system causing the sub standard performance increases.

3: He only tested memory transfer and not random access, page faults and all the other things that really slow your computer down.

If your after max performance then your going to buy the best anyhow, if you not then a PC still using PC133 memory will be fine.

actually, not completely true

[boarder]

He concludes that running memory clocked at the memory speed = FSB is better than running mem speed > or < than FSB. He never says that running 400MHz DDR at 333MHz will be slower than DDR333 at 333. If you bother paying extra for that faster RAM, you can run it at 333MHz and it will be just as fast...

The big thing about underclocking the bus speed, though, is that you can now overclock the latencies. You can make that CAS2.5 pc3200 a CAS2 pc2700 and tweak other latency settings, too. It also means that if you decide to upgrade to a 400MHz FSB Athlon, you'll be prepared with memory tested to support that.

This article is stupid because almost all of the tweaks affect latency, but his benchmark is bandwidth. Not much useful information can be gained from it. The Tom's article is much better, but you have to add other knowledge to use it correctly.