Everything You Always Wanted to Know About SDRAM (Memory): But Were Afraid to Ask
by Rajinder Gill on August 15, 2010 10:59 PM ESTIt’s coming up on a year since we published our last memory review; possibly the longest hiatus this section of the site has ever seen. To be honest, the reason we’ve refrained from posting much of anything is because things haven’t changed all that much over the last year – barring a necessary shift towards low-voltage oriented ICs (~1.30V to ~1.50V) from the likes of Elpida and PSC. Parts of these types will eventually become the norm as memory controllers based on smaller and smaller process technology, like Intel’s 32nm Gulftown, gain traction in the market.
While voltage requirements have changed for the better, factors relating to important memory timings like CL and tRCD haven’t seen an improvement; we’re almost at the same point we were a year ago. Back then Elpida provided a glimpse of promise with their Hyper-series of ICs. The Hyper part was capable of high-speed, low-latency operation in tandem. Unfortunately, due to problems with long-term reliability, Hyper is now defunct. Corsair and perhaps Mushkin still have enough stock to sell for a while, but once it's gone, that’s it.
The superseding Elpida BBSE variant ICs and a spread of chips from PSC now dominate the memory scene, ranging from mainstream DDR3-1333 speeds all the way to insanely-rated premium DDR3-2500 kits. Some of these parts are capable of keeping up with Hyper when it comes to CL, but do so by adding a few nanoseconds of random access latency due to a looser tRCD. Given that read and write access operations make up a significant portion of memory power consumption, this step backwards in performance may be a requisite factor for reliability – perhaps something was found by Elpida during the production lifetime of Hyper ICs that prompted a re-examination, leading to a more conservative recipe for data transfer/retrieval.
Today’s memory section comeback was fuelled by the arrival of a number of mainstream memory kits at our test labs – many of the kits we were using for motherboard reviews are no longer for sale so we needed to update our inventory of modules anyway. Corsair, Crucial and GSkill kindly sent memory from their mainstream line-ups. The original intent was to look at a few of those kits.
However, during the course of testing these kits, our focus shifted from writing a memory review (showing the same old boring graphs) to compiling something far more meaningful: a guide to memory optimization and addressing, including a detailed look at important memory timings, and an accounting of some of Intel’s lesser-known memory controller features. As such, this article should make a very compelling read for those of you interested in learning more about some of the design and engineering that goes into making memory work, and how a little understanding can go a long way when looking for creative ways to improve memory performance…
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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.