Searching for the Memory Holy Grail: Part 1
by Wesley Fink on July 27, 2003 11:13 PM EST- Posted in
- Memory
Intel White Papers Confirm Results
We have seen that SiSoft Sandra UNBuffered Memory benchmarks show four DIMMs to perform better than two in all configurations at DDR400 or higher base speeds on the 875/865 chipsets. However, MemTest86 Bandwidth and Sandra Standard Memory benchmark do not show improvement in going from two to four double-sided DIMMs. So why do we believe Sandra UNBuffered Memory benchmarks?
The answer, surprisingly, is in Intel 875P Chipset Memory Configuration Guide White Paper and the Intel 865P Chipset Memory Configuration Guide White Paper. The tables below are taken from Page 13 of the 875P White Paper, but the tables are identical in both the 865 and 875 documents, except that the first and second positions are reversed in the DDR400 chart for the 865. The Intel performance rankings exactly match the rankings we have measured using SiSoft Sandra UNBuffered Memory Test. It is interesting that UNBuffered Sandra was able to distinguish the performance differences between #1 and #2 –- four double-sided vs. two double-sided. This performance distinction was not apparent in either MemTest86 Bandwidth or SiSoft Sandra Standard Memory Test.
| DDR400 Performance Configurations on Intel 875/865 from Intel White Papers |
|||||
| DDR Speed | Number of DIMMS | Sides per DIMM | Mode | SC or DC | Performance |
| 400 MHz | 4 | 2 | Dynamic | Dual Channel | 1 (2 for 865) |
| 400 MHz | 2 | 2 | Dynamic | Dual Channel | 2 (1 for 865) |
| 400 MHz | 4 | 1 | Dynamic | Dual Channel | 2 |
| 400 MHz | 2 | 1 | Dynamic | Dual Channel | 3 |
| 400 MHz | 4 | any | Normal | Dual Channel | 4 |
| 400 MHz | any | 2 | Dynamic | Single Channel | 5 |
| 400 MHz | any | 1 | Dynamic | Single Channel | 6 |
| 400 MHz | any | any | Normal | Single Channel | 7 |
| DDR266/333 Performance Configurations on Intel 875/865 from Intel White Papers |
|||||
| DDR Speed | Number of DIMMS | Sides per DIMM | Mode | SC or DC | Performance |
| 233/333 MHz | 2 | 2 | Dynamic | Dual Channel | 1 |
| 233/333 MHz | 4 | 1 | Dynamic | Dual Channel | 1 |
| 233/333 MHz | 2 | 1 | Dynamic | Dual Channel | 2 |
| 233/333 MHz | 4 | 2 | Dynamic | Dual Channel | 3 |
| 233/333 MHz | any | any | Normal | Dual Channel | 4 |
| 233/333 MHz | 2 (1 in each channel) |
any | Dynamic | Single Channel | 5 |
| 233/333 MHz | 1 | 2 | Dynamic | Single Channel | 5 |
| 233/333 MHz | any | 1 | Dynamic | Single Channel | 6 |
| 233/333 MHz | any | any | Normal | Single Channel | 7 |
While we didn’t test Asynchronous 5:4 or 3:2 performance, or Memory Performance when using a 533FSB CPU, the DDR266/333 table should be useful for those situations. When running DDR333/266 as a base speed, two double-sided DIMMS or four single-sided DIMMS perform the fastest. Two single-sided DIMMs are second in speed performance, and four double-sided DIMMs – the fastest performer at DDR400 and higher – drops to third place.
Facebook
Twitter
RSS
42 Comments
View All Comments
jsalpha2 - Tuesday, July 29, 2003 - link
Pardon me, cause I'm tired. Did the article say if 4x(256) is better or worse than 2x(512). Assuming identicle brand and speed of RAM.I think I heard somewhere to go with just two sticks for better performance. Plus then you have open slots for later.
Question #2 Would 2x(512) of cheaper DDR333 be better than 2x(256) of DDR400?
thanks
Anonymous User - Tuesday, July 29, 2003 - link
Great article, it's just missing latency benchmarks.Anonymous User - Tuesday, July 29, 2003 - link
Ok - pardon the newbie question, but - I'm building a P4c with Asus P4P800 board. I want 1 gig of DDR400 ram - what brand/model number do I buy - ?Thanks for your help.
Anonymous User - Tuesday, July 29, 2003 - link
This is all nice and good, but what does it all mean in the real world, run some benchmarks in these various modes and show us whether we should care about it :) bottom line to me is what it does for the games, if i'm losing/gaining 4 FPS i'm more likely to care about the price differences then memtest.Wesley Fink - Tuesday, July 29, 2003 - link
These are quoted form Intel's White Paper, p.13 "NOTES: Ranks per Dimm (1 Rank is a single-sided DIMM, 2 Ranks is a double-sided DIMM)". The common practice of using higher-density Dimms every other Dimm on both sides (4 chips per side) is FUNCTIONALLY a Single Bank or Single-Sided Dimm.As for confirming that 4 dimms was faster, only the tests on the 3.0 were CPU-limited. We also determined maximum overclock on a 2.4C which was not CPU-Limited. Please check Page 7.
Philippine Mango - Thursday, January 25, 2007 - link
Wrong, you didn't use a 2.4C, you used a 2.6 processor which from what I know doesn't overclock as well as the 2.8C or 2.4C..Anonymous User - Tuesday, July 29, 2003 - link
"...we confirmed that the added memory bandwidth more than makes up for the slightly lower overclock with four double-sided DIMMs"To say you 'confirmed it' is quite a leap indeed... as you notably stated, you were CPU limited in going any higher for 1 and 2 sticks, whereas you clearly reached a blockade with the 4 sticks of memory. It could be that 4 sticks of memory causes a blockade in the chipset performance at some GHz, but with a better CPU you might have gone much higher with the opposing configurations.
-Robert
Anonymous User - Tuesday, July 29, 2003 - link
"If you plan to run DDR400 as your base memory speed with an 800FSB processor, your best memory performance will clearly be with four matched double-sided DIMMs"Can somebody help me to understand this?
I have only heard about 2 matched DIMMs...
Four matched DIMMs is 2 X 2 matched DIMMS?
Thank you very much!
Anonymous User - Tuesday, July 29, 2003 - link
While the article was interesting in that it at least confirmed Intel's white paper, I would be interested in your also testing ECC. I have a machine which does double duty as a backup server (plug the disks in the SCSI port and away it goes!). I am just curious as to the performamce hit when ECC is being used.Anonymous User - Tuesday, July 29, 2003 - link
The writer does not distinguish between DS and double bank module ;)