RAM Timings Guide - Overclock.net

onelivestarfish · 08-29-07

So often we ask the questions: What are these timings/subtimings for?

Well here are the answers.

Each chipset (680i/975/965) acts differently to how timings are applied. Some of you are probably familiar with how DDR1 ram acted on timings - DDR2 acts a bit differently and some timings are less important than what they used to be.

The EVGA 680i SLI board has an entire bios section dedicated to ram timings. So why not do some tweaking.
The guide follows the bios order, skipping Command Per Clock which is saved for last.

tCL:
Large influence on stability / Medium influence on bandwidth
From CAS 5 to 4 results change ~5-10mb/s. The same change will most likely be seen when going to CAS 3. This timing is widely seen as most important (Command rate disregarded).
Recommendation: 4 for normal usage, 5 when oc"ing. Tweaked: 3.

tRCD:
Medium influence on stability / Large influence on bandwidth
tRCD going from 4 to 3 gives ~15mb/s. From 5 to 4 also yields 10-15mb/s. This timing is considered second important after CAS, but actually it"s more important on 680i/DDR2.
Recommendation: 4 for oc/normal usage. 5 if you want to push mhz. Tweaked: 3

tRP:
Medium/small influence on stability / Small influence on bandwidth
Results vary close to nothing when changing from 3 to 4 to 5. Still this timing needs to finish its cycle before a new one starts, so dont set it higher than 5.
Recommendation: 4 for oc/normal usage. 5 if you want to push mhz. Tweaked: 3

tRAS:
Small influence on stability / Small influence on bandwidth
tRAS seems to act differently on integer/float results. Integer, going from 15 to 10 changes by ~5mb/s. Float doesnt change.
tRAS is an "end-timing", so dont go to high. And not lower than what tCL+tRCD equals.
Recommendation: 12 for oc/normal usage. 15 if you want to push mhz. Tweaked: 8

tRRD:
Small influence on stability / Small influence on bandwidth
tRRD of 2 didnt change the results. Nor did a tRRD of 4. This is a delay-timing so a too low value may result in recalculation.
Recommendation: Auto for oc/normal usage. 4 if you want to push mhz. Tweaked: 2

tRC:
Medium influence on stability / Large influence on bandwidth
This timing is quite surprising. Going from 30 to 21 gave ~90mb/s. From 23 to 21 gave ~15-20mb/s.
tRC is last timing before ram burst (data transfer).
Dont set too high. And tRC should be greater than tRAS + tRP or you might get corruption.
Recommendation: 21 for normal usage. 30 if you want to push mhz. Tweaked: 15

tWR:
Small influence on stability / Small influence on bandwidth
Small change from 6 to 3. Setting timing too low will cause ram to fail switching to "read mode".
Recommendation: Auto for oc/normal usage. 6 if you want to push mhz. Tweaked: 3

tWTR:
Large influence on stability / Small influence on bandwidth
From 10 to 8 didnt change results. 6 would lock up the system. This timing gives no bonus but affects stability a lot. Use with care.
Recommendation: Auto for oc/normal usage. 10 if you want to push mhz. Tweaked: 8(7)

tREF:
Small influence on stability / Small influence on bandwidth
Changing to 3,9us didnt show improvements in benchmark. It also didnt seem to affect stability. tREF was important with DDR1.
Recommendation: Auto for oc/normal usage. 7,8us if you want to push mhz. Tweaked: 3,9us

Command Rate:
Settings are 2T/1T. You probably already know a lot about this timing.
The 680i struggles running 1T above 800mhz. So do the ram - atleast 2,2v are needed. This timing gives a great boost to bandwidth, but is fairly hard to attain. I wont recommend any setting regarding this timing. You need to find what mhz you get with 1T, then find mhz with 2T, then compare benchmarks.

Post words:
The tRC and tRCD are two timings to take notice of. They yield good results compared to how they affect stability.
CAS isnt as important as in the DDR1 days. You might even say timings in generel arent as important as with DDR1.

Hope this helps everyone

Source: EVGA Forums (RAM TIMINGS)

MasterShake · 08-30-07

I see it was made for the 680i chipset but are these definitions universal for say, my 590 amd chipset?

Fishie36 · 08-30-07

Wow this is sweet to have. Ram timings have always been one of my worst areas. I'm printing it out and hanging it on my wall

kevg73 · 08-30-07

do you think you could write out the full names of those timings? my bios has them out in words instead of abbreviations. its like read recovery (i think = command rate), read-write delay, etc.

Rick Arter · 09-01-07

WOW thats the most in-depth RAM timing explanation ever rep+ for you. Now I can fully tweak my G.Skill NQs for better benches thanks.

Ron.L · 09-07-07

Very detailed and nicely done, Reps +!

StormX2 · 09-10-07

i forgot where the post is

but it had pretty much difinitive proof showing that lower timing with higher oc was better performance than tighter timings and a slightly lower oc.

testing 800 and 1066 mhz memory runnin 5-5-5-15 seemd to be just fine for performance when at 1066 mhz

this was a good explanation

rep+

Ravin · 10-07-07

Finally.....Someone who has the answer to the question I been asking myself....

I think that I'll start to tweak the advanced timings and at least have an idea of what I'm doing.

+rep

Dostoyevsky77 · 10-09-07

Yeah. REP+ for advanced timings description, esp tRC, which will have a very good effect on my tight timings.

Ravin · 10-14-07

Quote:

Originally Posted by onelivestarfish

tRC:
Medium influence on stability / Large influence on bandwidth
This timing is quite surprising. Going from 30 to 21 gave ~90mb/s. From 23 to 21 gave ~15-20mb/s.
tRC is last timing before ram burst (data transfer).
Dont set too high. And tRC should be greater than tRAS + tRP or you might get corruption.
Recommendation: 21 for normal usage. 30 if you want to push mhz. Tweaked: 15

Funny- tRC does not do anything for improving my setup. From 31 to 30 to 21 to 16 to 14 to 12 makes almost no difference in the benchmarks for bandwidth, latency, or overall performance. Each bench was within 0.01% of the others- not enough to be statistically different.

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RAM Timings Guide

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