Everything You Always Wanted to Know About SDRAM (Memory): But Were Afraid to Ask
by Rajinder Gill on August 15, 2010 10:59 PM ESTWe hope you’ve enjoyed reading this article as much as we’ve enjoyed putting it together. If you took the time to thoroughly peruse and digest the information within the intricacies of basic memory operation should no longer be such a baffling subject. With the ground work out of the way, we now have a solid platform from which to build as we more closely begin exploring other avenues for increasing memory performance. We’ve already identified additional topics worth discussing, and provided the time shows up on the books, plan to bring you more.
Assumedly, the one big question that may remain: What are the real world benefits of memory tuning? Technically, we covered the subject in-depth last year in a previous article. We suggest you read through it once again for a refresher before you embark on any overclocking journeys (or before you rush out to over-spend on memory kits). Everything written in that article then is just as valid today. We’ve run tests here on our Gulftown samples and found exactly the same behavior. Undoubtably, Intel have taken steps to ensure their architectures aren't prematurely bottlenecked by giving the memory controller a big, fat bus for communicating with the DIMMs.
From what we can tell, the next generation of performance processors from Intel are going to move over to a 256-bit wide (quad channel) memory controller, leaving little need for ultra-high frequency memory kits. Thus we re-iterate something many have said before: a top priority when it comes to improving memory ICs and their respective architectures should be to focus development on reducing absolute minimum latency requirements for timings such as CAS and tRCD, rather than chasing raw synthetic bandwidth figures or setting outright frequency records at the expense of unduly high random access times.
Stepping away from the performance segment for a moment, something else that's also come to light is rumored news that Intel's Sandy Bridge architecture (due Q1 2011) will, by design, limit reference clock driven overclocking on mainstream parts to 5% past stock operating frequency. If this is indeed the case the consequence will be a very restricted ability to control memory bus frequency with limited granularity to tune the first 50~70 MHz past each step, followed by mandatory minimum jump of 200MHz to the next operating level. Accessing hidden potential will be even more difficult, especially for users of mainstream memory kits. While there is no downside to this from a processing perspective (hey, more speed is always better), this could be another serious nail in the coffin of an already waning overclocking memory industry.
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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.