Everything You Always Wanted to Know About SDRAM (Memory): But Were Afraid to Ask
by Rajinder Gill on August 15, 2010 10:59 PM ESTHere at AnandTech we decided to go the extra mile for you, our loyal reader. A few weeks back we approached ASUS USA Tech Support with a request to set-up a technical consultation with their Firmware Engineering Department. After passing along our request, what came out of the meeting was a special beta BIOS that added a number of previously unavailable memory tuning registers once excluded from direct user control.
In the interest of full disclosure, we did request the same help from EVGA and although they were willing to back our play, technical difficulties prevented them from delivering everything we had originally hoped for.
Seen below, these new registers are: Adaptive Page Closing, Adaptive Timeout Counter, Request Counter, Max Page Close Limit, Min Page Close Limit, and Mistake Counter. As suspected, the first setting is used to enabled or disable the feature entirely. Interesting enough, Intel chose not to enable this feature by default; so we leave it up to you.
Click to enlarge
A short description of each register is shown below (taken from Intel Core i7-900 Desktop Processor Extreme Edition Series and Intel Core i7-900 Desktop Processor Series Datasheet, Volume 2, page 79, dated October 2009). Be aware the source most likely contains at least one known error. In particular, Intel has provided exactly the same description for Adaptive Timeout Counter and Mistake Counter. As well, the bit count for Mistake Counter in the table does not match the value in the text, further suggesting someone goofed.
Once you've had time to fully digest the information above - and ponder how awesome we are - we would like to cordially invite you to do some of your own testing and report your results at our forums. AnandTech readers with a valid login can download ASUS Rampage III Extreme BIOS release 0878 now. We haven't really had a chance to do any significant experimenting with what little spare time we have and we need your help exploring uncharted territory...
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Dwebtron - Monday, August 16, 2010 - link
How did you know I was afraid to ask!!0ldman79 - Tuesday, May 28, 2019 - link
It's because we're all from the future.neslog - Monday, August 16, 2010 - link
Thank you for a great article on memory and you are right, I was afraid to ask.landerf - Monday, August 16, 2010 - link
I've found for the i7 platform the perfect ram setup is 1200 Mhz + cas5 or 6 timings, a 3:1 uncore ratio, and a B2B of 4. Not only does this perform well even in synthetics, it provides the "smoothest" intel experience. Something people who use amd and intel have been complaining about intel lacking. Check this chart and see how well that setup performs compared to all the conventional 2:1 setups. https://spreadsheets.google.com/ccc?key=0AsaXlcTga...Servando Silva - Monday, August 16, 2010 - link
Thanks for a great article. It will take me a while to read it carefully and fully understand it.Kris + Raju = Killer combo.
neslog - Monday, August 16, 2010 - link
On page 8 you may want to change the wording in the last paragraph " Once you've had...to cordially invite[d] (you) to do some..."
Thanks again for the article. I appreciate all the work that went into putting it together
elforeign - Monday, August 16, 2010 - link
It's a site willing to go the extra mile like this to report and educate the masses that are truly worth the time to peruse and read the posted articles. I check this site daily because there is always something interesting to read. Thank you to all the staff who do a great job here!chizow - Monday, August 16, 2010 - link
Just kidding....Or am I? :D
JarredWalton - Monday, August 16, 2010 - link
There's obviously benefits to either direction. Reducing latency is definitely a priority, but something not mentioned in the text that bears repeating is that latency is a factor of clock speed as well as the various timings. While CAS 6 will always be better than CAS 7 at the same base clock (and likewise for the other timings), if you have a faster memory speed CAS 7 could end up being better.So here's the scoop:
DDR3-1066 = 266MHz base clock, or 3.75ns per cycle.
DDR3-1333 = 333MHz base clock, or 3.00ns per cycle.
DDR3-1600 = 400MHz base clock, or 2.50ns per cycle.
DDR3-2000 = 500MHz base clock, or 2.00ns per cycle.
That gives this table in order of increasing latency, with rough pricing for 2x2GB. Based on pricing and latency, I've starred the best buys on Newegg:
CAS 6 DDR3-2000 = 12.0ns. ($180)
CAS 7 DDR3-2000 = 14.0ns. ($140)
CAS 6 DDR3-1600 = 15.0ns. ($115) ***
CAS 8 DDR3-2000 = 16.0ns. ($150)
CAS 7 DDR3-1600 = 17.5ns. ($101) ***
CAS 9 DDR3-2000 = 18.0ns. ($100) ***
CAS 6 DDR3-1333 = 18.0ns. ($100) ***
CAS 10 DDR3-2000 = 20.0ns. ($118)
CAS 8 DDR3-1600 = 20.0ns. ($85) ***
CAS 7 DDR3-1333 = 21.0ns. ($90)
CAS 9 DDR3-1600 = 22.5ns. ($92)
CAS 8 DDR3-1333 = 24.0ns. ($92)
CAS 7 DDR3-1066 = 26.3ns. ($80)
CAS 9 DDR3-1333 = 27.0ns. ($85)
CAS 8 DDR3-1066 = 30.0ns. ($93)
Notice how the total latency often comes in groups. The DDR3-1333 CL6, DDR3-1600 CL7, and DDR3-2000 CL9 are all priced around $100. If you buy any of these modules, there's a good chance (though YMMV) that you can tweak timings to run at whichever value makes you happiest. I'd probably err on the side of buying the higher speed rated modules, though, or at least grab the 1600MHz set.
Rick83 - Monday, August 16, 2010 - link
Your pricing comparison is sadly missing one important factor:Operating voltage.
I was at first surprised by the high cost of 1333/9, but I expect the voltage of that kit to be around 1.5, where most 1333/7 kits already clock in at 1.65.
The 2000/9 kit probably also runs higher V's than the identically priced 1333/6?
Lower voltages are usually preferred, as they give you a) more headroom and b) less heat at stock - with on-die controllers even less cpu heat.