Searching for the Memory Holy Grail: Part 1
by Wesley Fink on July 27, 2003 11:13 PM EST- Posted in
- Memory
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.
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Anonymous User - Sunday, August 31, 2003 - link
This single/double side/bank issue is very misunderstood. To further confuse things the memory manufacturers, who finally getting better about reporting full timing numbers, generally don't publish the side/bank count. I'd like to see an article that helps identify whose memory is really double banked, especially at the 256MB level, since its going to take 4 modules for best performance in an 875 system. Since many of these products are best available thru the internet, I don't have the luxury of looking at the modules before I buy.FYI, I'm also more interested in using well matched double banked components with low timings than in overclocking to the max.
Mushkin has very low timing memory in a 512MB configuration that is double-banked, but it seems like overkill to put 2GB of memory for $800+ into the system at this point. (I also don't know how well the system would perform with this quantity of memory as I hear that more memory can slow timings down.) Their 256MB modules are single-banked unfortunately.
Anonymous User - Monday, August 18, 2003 - link
I would personally buy the Mushkin PC3200 Level II Dual Pack located at this URL: http://www.mushkin.com/epages/Mushkin.storefront/3...It says that is is CAS 2-2-2 at 400MHz
Unfortunately, Anandtech has not added Mushkin to their test products for any of these articles (not that I have seen at least) so I cannot verify the performance. I hope this due to Mushkin not supplying them samples before they complete testing and go to press. Otherwise, it is just a gross oversite by Anandtech not to include Mushkin. Whatever the case, Mushkin is a big name company with many supporters who will vouch for their quality. I am going to upgrade my memory shortly to these exact DIMMs so I feel comfortable suggesting them. 2-2-2 latency just sounds too good to pass up.
Cheers,
Wiley
DaveH - Tuesday, August 12, 2003 - link
What about running slower RAM in the newer chipsets? Like PC2100 in 800 FSB?Anonymous User - Monday, August 11, 2003 - link
My personal SiSoft Sandra Memory Bandwidth UNBuffered test results on a Gigabyte 8KNXP (F5 BIOS) with a P4 3Ghz/800Mhz, ATI9800 Pro 256mb, SB Audigy:Mushkin PC3500 Level II Black
4x512mb, 200mhz, 2-2-2-6, 2955/3017
4x512mb, 217mhz, 2-2-2-6, 2850/2916
2x512mb, 200mhz, 2-2-2-6, 2844/2862
2x512mb, 217mhz, 2-3-2-6, 2423/2493
Corsair TWINX1024-3700
4x512mb, 200mhz, 3-4-4-8, 2724/2782
4x512mb, 217mhz, 3-4-4-8, 2614/2723
2x512mb, 200mhz, 3-4-3-8, 2610/2626
2x512mb, 217mhz, 3-4-3-8, 2491/2542
Anonymous User - Thursday, August 7, 2003 - link
Need help determining SS vs DS (Single side/bank vs. Double Side/Bank) - how can you tell, as the memory mfgrs don't usually say?Rayalkj - Thursday, August 7, 2003 - link
How similiar does the RAM have to be? I bought a Dell with 2x128 meg ram and want to up it to 512 megs. Do I need the exact same Brand? Just the same sizes? (ie. 2 more 128 meg sticks) Is there something I should look for especially?... Yes, I am a bit of a noob at this stuff
Anonymous User - Wednesday, August 6, 2003 - link
Would this apply to nForce2 Ultra chipsets?Wesley Fink - Sunday, August 3, 2003 - link
Regarding "Mixed Memory" configurations, the Best Memory Timings are the fastest timings THAT PARTICULAR COMBINATION WOULD RUN. So they are the best timings for that mix of Dimms. Mixed pairs - particularly widely different memory pairs - can take a very large performance hit in 865/875 boards. The reduction in performance is MUCH greater than we would expect.As was also stated, we have seen cases of 2 pairs of dimms from different manufacturers that match closely on capacity and timings that perform just as well as 2 matched pairs.
Anonymous User - Sunday, August 3, 2003 - link
Re: "Intel’s White Papers address mixed memoryconfigurations only to say that they will work,
but they will default to the slowest speed and
SPD timings of the mixed DIMMs."
I wish I understood this. I am pretty sure that
I don't. For example, in the first row of the
mixed memory benchmark table the "best memory
timing" is given as 2-7-3-3 but the 512 MB DIMMs
are said to run at 2-5-2-2. Could it be that this
column should be labelled "worst memory timing"?
And suppose that the 512 MB memory was run at the
slower timing, 2-7-3-3, instead of 2-5-2-2.
How does that result in a 25% performance loss?
I would really like to understand this so that
I could predict what will happen when I mix
memory timings, avoid really bad DIMM
combinations and be able to use the not so bad
combinations. So, can someone explain what it
really going on here?
MS - Friday, August 1, 2003 - link
I'll certainly run a few benches myself. It is really interesting that those guys who should know, that is memory and chipset manufacturers are lagging so far behind the "fanboy" community in terms of understanding how things actually work and what factors are really important.As far as your review goes, I am eager to see it, especially the acknowledgement (LOL)
Michael