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Memory Overclocking on the DFI NF680i LT


I recently spent some time overclocking my Mushkin PC2-8500 2x2GB sticks on the DFI NF680i LT. Given my current max stable overclock is at 400x8, I decided to try and get the lowest latency at 1T that was possible at a 1:1 DDR2-800 speed and then focus on using unlinked mode to get the highest MHz possible out of this RAM at a 2T command rate.




Interesting Observations:
  • 4GB vs 2GB: I was expecting the 4GB kit to be much less cooperative than a typical 2GB kit, but I was pleasantly surprised that at max rated voltage of 2.3V, this RAM can both run well at low latency at 1T and high MHz at 2T with relative ease. Vista x64 loves RAM and it's working smoothly so far. The only hiccup I had was during the Vista x64 install... See my Tips/Tricks article for more info.
  • 1T vs T2: As you will see, 800MHz at 1T is faster than 1120MHz at 2T. I could maintain 1T at 2.3V up to 900MHz but the performance suffered running out of sync. I really need a BIOS that allows me to set the x8 multi on my X3220 so I can try to run 450x8 and increase memory performance by running 1T at 900MHz.
  • CAS: Even increasing the voltage above rated values would not allow the machine to POST with CAS3 with this RAM. CAS4 is the sweet spot for low-latency... CAS5 at high MHz.
  • Testing: Memtest+ 1.7 is a great tool for testing RAM, but it takes about 45 minutes to do a full pass with 4GB. As a rule of thumb, I always test any RAM overclock with a pass of Memtest before booting Windows and have never had a corrupt OS as a result. Of course, once in Windows, Super Pi and Everest are great quick benchmarking tools.
  • Voltage: As with most Voltage settings in BIOS on the DFI NF680i LT, the DRAM Voltage needs to be set higher than actual... usually by 2 steps... that is on my machine setting 2.38 = 2.30 actual. Under load Vdimm will only droop about 0.01V. I verified SmartGuardian with my DMM and it was usually within 0.01V as well.
  • Timing Guide: I used Illumanati's 680i RAM Timing Guide in establishing my baselines. I'll repeat his advice here for the benefit of everyone else along with my own comments...


Illumanati's RAM Timing Guide:

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.
[VR: As mentioend above CAS3 = No POST!; CAS4 at 800MHz; CAS5 at 1120MHz]

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
[VR: Used 3 at 800MHz and 5 at 1100MHz]

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
[VR: I used 3 at 800Mhz and 5 at 1100MHz]

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
[VR: At 800MHz I tried 6 and 8 with no noticable difference in SuperPI or Everest. I think at 6, the RAM/NB is ignoring this setting as this is less than tCL+tRCD; At 1100MHz I used the Mushkin SPD value of 18]

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
[VR: Used recommended values of 2 at 800MHz and 4 at 1100MHz]

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
[VR: I tried a variety of tRC values from 1 to 12 at 800MHz... it made little to no difference and I suspect ultra low settings are being ignored by the RAM/NB anyway. At 1100MHz, I used the recommended value of 30]

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
[VR: I tried values from 3-5 at 800MHz with little to no difference. I used 6 at 1100MHz]

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)
[VR: I tried 7, 8, and 9 at 800MHz with no difference. I used the recommended value of 10 for 1100MHz]

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
[VR: I tried setting this to 3.9us in BIOS but Memset showed it at 7.8us so I wonder if BIOS was ignoring my setting? I ended up just leaving it at 7.8 for both 800MHz and 1100MHz]

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.
[VR: 1T was easy to achieve at 800MHz and was actually stable up to 900MHz. Obviusly, 2T was used for 1100MHz.]


Screen-shots and Benchmarks:

(Click any pic to enlarge.)

800MHz 1T BIOS Memory Timing Screen...



800MHz 1T PRIME stable for 9+hrs...



800MHz 1T Everest Benchmark Results...



800MHz 1T SuperPi 1M...



800MHz 1T SuperPi 32M...



1120MHz:

1120MHz Everest Benchmark... (note higher latency and lower bandwidth than 800MHz at 1T)



1120MHz SuperPi 1M...



1120MHz SuperPi 32M...


Virtual if it wasnt for your blog I would of gave up on this board, Really appreciate all the time you've spent and all the info you have shared it has been soo very helpful.

Cool! Glad I've been able to give back in some way as I've learned a lot from the community over the years myself.

Thanks for the resource!
SGarv

Great job man! ;) Thanks to U i`m doing now 3.8GHZ orthos stable.

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