What speed memory should you use to get the best from Core i7?
We had a torrid time trying to raise the memory speed to 1600MHz on the EVGA X58 SLI. This is something of a puzzle as the EVGA manual explicitly states that the board supports memory speeds way beyond 2000MHz. Furthermore, the EVGA forums give a detailed guide to overclocking.
We spent ages trying all manner of settings and different types of memory, but we got nowhere fast. It was time to switch motherboard yet again. This time we tried an Asus P6T SE and suddenly we found that the memory would run at really high speed.
SiSoft Sandra Results
Memory Bandwidth in Gigabytes per Second (GB/s)
Longer bars are better
Memory Latency in Nanoseconds (ns)
Shorter bars are better
We installed a Core i7 965 Extreme processor on the Asus along with 3x1GB Kingston HyperX DDR3-2000 running 32-bit Vista and tested the memory running at 1066MHz, 1333MHz, 1600MHz and 1866MHz. SiSoft Sandra showed that the memory bandwidth increased by 10GB/s from 18GB/s to 28GB/s.
This enormous change was barely reflected in PCMark Vantage as the Overall score barely changed one iota. The most obvious benefit of the increased memory speed was in the Productivity section of the benchmark but generally speaking the results were unimpressive.
We were unconvinced by these results and installed 6x2GB of OCZ Reaper DDR3-1800 on the Asus running on 64-bit Vista. Increasing the amount of memory from 3GB to 12GB yielded improvements in Vantage's Overall results. However, the 12GB system didn’t show any benefit when we increased speed from 1066MHz to 1333MHz and onwards to 1600MHz. The figures show that the Gaming element of PCMark Vantage increased as the memory speed got higher, but the Productivity test results decreased. That’s right the results decreased where they increased on the 3GB 32-bit system. Historically, we've found that PCMark Vantage is a very good guide of system performance.
PCMark Vantage Results
Longer bars are better
Don’t get stressed about running a high memory speed on Core i7. You’re probably better off using 1333MHz than 1066MHz, but we are sure that 1600MHz and higher speeds are a fruitless exercise.
@Dustin... be sure you comprehend before accusing someone of being ignorant
Ian didn't say Windows "couldn't do PAE - period". He said it couldn't do PAE because too many drivers couldn't handle it, having not been written with PAE in mind.
Yes, I find it truly surprising that an 8-DIMM dual-opteron setup was not tested in this article for Core i7 memory configs!!
This is very worthwhile reporting!
It is little known that the only fully performant memory configuration for dual processor AMD Opterons has been exactly 8 DIMMS of identical density, 4 on each socket, at least according to my tests. Other configurations give poorer measured performance, which may or may not be reported by the BIOS.
I have only tested with an in house tool, Opteron versions up to Barcelona. Anybody concerned about memory performance should repeat the tests on more modern hardware.
I find it amazing that such basic information is not clearly documented and is also rarely tested and reported-...
@jolyon - Yes, it's mainly a driver issue
Here is what Microsoft say on the issue -
And the wikipedia page on Physical Address Extension says -
"However, desktop versions of Windows (Windows XP, Windows Vista) limit physical address space to 4 GB for driver compatibility reasons."
Microsoft themselves confirm that >4GB is a no-go with 32-bit XP and Vista.
So, very limited PAE with Windows on the desktop and deeply scary compatibility issues with PAE on both servers and desktop. We've tried PAE on desktop and server Windows and it quickly became clear that the pain of moving to 64-bit was less than the pain of trying to get PAE stable and effective.
With Linux, we installed a PAE kernels, rebooted, and the servers all worked exactly as before but with much more memory. We are now moving to 64-bit (with virtualisation where required) but it has bought us a few years.
It matches my rule of thumb ...
... which says that more bog-standard memory trumps less but faster memory every time.
Slightly surprised that 3-channel offers no noticeable advantage. Perhaps it's time will come with future iterations and speed steps of Intel's new architecture. Anyway, there's a financial advantage: 12Gb without needing to buy expensive 4Gb DIMMS.
PAE and multicore CPUs means that 8Gb or even 12Gb may be sensible with 32-bit Linux: 2Gb or 3Gb per process, each running flat out in its own core. But if you aren't constrained by some sort of historical relic, 64-bit Linux should be today's default. I doubt I'll be doing many new 32-bit installs in the future.