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Searching for the Memory Holy Grail: Part 1

 by Wesley Fink on July 27, 2003 11:13 PM EST
42 Comments | Add A Comment
42 Comments

Mixed Configurations

In general, Intel’s White Papers assume that you will be using two or four matched DIMMs. The reality for many users, however, is that while they may have a pair of matched DIMMs, they do not likely have four matched DIMMs at their disposal to use in their new 865/875 boards. Intel’s White Papers address mixed memory configurations only to say that they will work, but they will default to the slowest speed and SPD timings of the mixed DIMMs.

To get a better idea of what happens to performance when mixing DIMMs at default performance at DDR400/800FSB, refer to the statistics below.


DIMM Configuration Best Memory Timing UNBuffered Sandra 2003 Memory Test
(MB/Second)		 % Changed from Matched DIMM Performance
2x256MB DS + 2x512MB DS 2-7-3-3 2094 INT
2148 FLT		 -25%
2x256MB DS + 2x256MB SS 2.5-7-3-3 2064 INT
2132 FLT		 -22%
2x512MB DS + 2x256MB SS 2.5-7-3-3 2097 INT
2150 FLT		 -23%
4x256MB Matched DS 2-7-3-3 2861 INT
2848 FLT		 ----


The performance declines significantly from mixing different pairs of memory, even with two pairs of matched dual-channel. A 22% to 25% drop in memory performance compared to four matched double-sided DIMMs is certainly nothing to sneeze at.

Undoubtedly, the memory modules themselves are having an impact on this drop in performance. However, the four matched DIMMs run at 2-7-2-2, which is certainly not the best score I have seen at DDR400. In fact, the 2x512MB DS pair used in the mixed tests run as a dual-channel pair at DDR400 with 2-5-2-2 timings. The SS pair of 256MB DIMMs do require CAS 2.5 for best performance, and run fine as a pair at 2.5-6-3-2 at DDR400. Yet, these slower SS DIMMs perform better mixed with the DS GOLD modules than the faster DIMMs.

There will be great variation in mixed DIMM performance, with some close DIMMs running much better than these results. However, you can clearly see from the results that the very best performance at 1:1 requires four matched DIMMs. The performance loss from running two different matched pairs of DIMMs can be enormous.

Intel White Papers Confirm Results FSB Overclocking with 1, 2, and 4 DIMMs
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  • Wesley Fink - Friday, August 1, 2003 - link

    Thanks, Michael. Your comments are appreciated, since your memory reviews are always a "must read" for everyone in the industry.

    I got an idea for an article from your review of OCZ3700 GOLD at Lost Circuits. When it posts at AnandTech, I think you will find it interesting.

    You may want to look at some of ThugsRook's game benches posted in the Forums here. As a skeptic he was trying to prove SS/DS made no difference in game benches. What he found, however, was that SS game benches were consisitently lower than DS benches. The differences were smaller than we see with SiSoft unbuffered, as expected, but they appear to be genuine.

  • MS - Friday, August 1, 2003 - link

    Nice review, Wes.

    One single issue I have is that if you are running SiSoft unbuffered, you constantly hammer the memory, which means that the idle counter will not go in effect and you keep the maximum number of pages open at all times (I believe it is 32 combined to 16 wide pages in dual channel mode). This is really why you see the performance benefit with double-sided DIMMs.

    However, in real life applications, this benefit is not present, at least as far as I can tell. No criticism intended, just a side-note.

    Regards
    Michael

    p.s. and the guys who did some of the performance studies at Intel used to call me quite a few times .. :-)

  • Anonymous User - Friday, August 1, 2003 - link

    This reads too much like an ad by OCZ - any non-OCZ users of the P4P800 Deluxe Asus board got a recommendation for best memory sticks to get stable, solid 1 gig of DDR333 (little, if any OC)? Thanks

  • Anonymous User - Friday, August 1, 2003 - link

    In fact OCZ announced PC-3700 Gold Quad pairs at 2003-07-03 for Intel 875 chipset.:

    SUNNYVALE, CALIFORNIA
    OCZ Announces Dual Channel Gold Quad kits.

    OCZ is pleased to announce the release of OCZ PC-3700 Dual Channel Gold EL DDR memory in 1GB kits featuring quad 256mb modules based on OCZ's recently developed Hyperspeed and Extended Voltage Protection (EVP) technologies.

    OCZ HyperSpeed® technology denotes specific OCZ EL DDR ICs built and selected for their ability to run at the highest possible frequency. EVP protection allows the modules to tolerate higher voltage without compromising stability.

    "OCZ PC3700 Gold has been a dominant product," said Steve Lee, Director of Strategic Business Development. "By offering hand-tested and matched quad 256mb modules, we have the best solution for dual channel configurations on the market."

    OCZ Dual Channel Gold Quad memory will be shipping in 1GB PC-3700 Dual Channel optimized kits rated at CL 2-3-7-3 with an operating frequency of 2.75 volts. Each module is backed by OCZ's Lifetime Warranty and features a Gold layered copper heatspreader. The four matched 256MB modules are tested together on the Abit IC7-G to ensure maximum stability and performance.

    OCZ Dual Channel Gold memory has been designed specifically for use with the Intel Canterwood and Springdale chipsets, and thus offers the best performance on these platforms

  • Wesley Fink - Wednesday, July 30, 2003 - link

    512MB Dimms are usually DS, but that will be changing with higher-density chips coming out. @56MB Dimms are normally SS right now, but there are exceptions like OCZ 3700 GOLD which are 256MB and Double Bank. The last page of the article has charts which give recommendations from best to worst performance based on memory configuration. The data is from our own testing and the Intel White Papers.

    We will include some game benches in Part 2, but ThugsRook, who regularly posts in the Anand Forums, has posted some game benches at several sites showing the performance difference in SS and DS memory modules in gaming performance.

  • Anonymous User - Wednesday, July 30, 2003 - link

    Thanks (#25) - I too have noticed that memory vendors claims and board manufacturer compatibility charts are often at odds - seems like it's left up to the builder to actually try it and see if it runs ... (ref post #19).

  • Anonymous User - Wednesday, July 30, 2003 - link

    I noticed that Asus in their P4C800 description (on their web page) says that some manufacturer's memory can only be used in certain configurations - some branda are limited to 2 sticks and some are limited in the total GB size.
    The reason they say is: "For optimum performance and overclocking stability". But if true it was rather surprising. For example, in the case of Kingston memory, Asus only two 512 sticks can be used.

    I pointed this out to Kingston and they simply responded that four sticks can be used for a total of 2 GB. The tech ignored making any comment about the Asus statement.

    So I suppose 4 sticks can be used as long as you run them at the stated settings. But I am not sure Asus means about "optimum performance".

  • Anonymous User - Tuesday, July 29, 2003 - link

    Some real world benchmarks wure would have been nice, even if only 640x480 Quake3 numbers, just to get an idea if there really is a payoff to warrant the added cost that filling 4 banks vs 2 would entail.

  • Anonymous User - Tuesday, July 29, 2003 - link

    I'd also like to see what this means in the real world. I would be interested in some gaming benchmarks, particularly UT2003.
    Thanks for the excellent article!

  • Anonymous User - Tuesday, July 29, 2003 - link

    Hey Prometheus, please check this asap:
    http://www.overclockers.com/tips00438/
    great article btw ;)
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