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Overclocked RAM Timings

F

FireDemon

Limp Gawd
Joined
Feb 10, 2006
Messages
256
Back in the olden days of lore, I had much experience playing around with CPU frequencies and vcore settings. I got big into overclocking and voltmodding vid cards, but never really so much RAM. So I am here today to ask a rather simple question.

I have 4GB of crucial ballistix PC6400 (800) which I have OC'd to PC8500 (1066). Stock voltage is 2.0, and it is Prime95 stable at 2.2V however right now I am stress testing it at 2.15 as I want stability with the least amount of voltage required. My question is regarding the timings. Stock timings at 800 speeds are 4-4-4-12. At 1066 speeds I had to relax the timings to 5-5-5-15. If I were to feed the RAM even more voltage than what is required to remain stable at 1066, could I then stay clocked at 1066 AND yield better timings than 5-5-5-15 or are those timings pretty much as good as It's going to get at 1066 speeds?

I am going to watercool this RAM very soon to help with the extra heatload.
 
you'll probably be unlikely to tighten timing at 1066 any more than they currently are up to 2.2v and personally I wouldn't try to push voltage more than that.

are you running at 1t(1n) command rate? if not you'll have to loosen your timing a bit to get it stable if it'll take, but it will show better performance. 1066 5-5-5-15 1t is nothing to really sneer at imo and if you can't get them any tighter I wouldn't worry about it. you don't need CAS, TRCD, TRP to be uniform, if you can drop CAS +/- TRAS and possibly TRP any more and remain stable you'll see a gain.

another good quick(ish) test for ram stability is memtest86+'s test #5. around an hour and a half of looped testing should be good enough, but some will go as far as letting it run for 24 hrs (I think it's kind of overkill myself, lol).
 
I'll try memtest 86, but so far at 2.2V the system is Prime95 stable after a solid 5 hours. I thought I had it locked down @ 2.15V until the system hard locked and reset while playing Bioshock.

Command rate is currently at 2T and bank cycle is at 31.
 
You could move tRCD up 1, probably from 3 to 4, or increase tRFC (say between 40 and 50) to increase stability, especially for crucial and especially is you have 4gb (4x1gb)....ie., all 4 slot taken up. You can relax tRAS too.
 
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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
 
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