What quantity of memory should you install in your Core i7 system?
Once we had settled on the Asus P6T SE motherboard with OCZ Reaper memory we carried out a final simple test. We benchmarked the system with 12GB of triple-channel memory and then reduced the amount of memory for subsequent tests.
PCMark Vantage Results
Longer bars are better
SiSoft Sandra Results
Bandwidth
Memory Bandwidth in Gigabytes per Second (GB/s)
Longer bars are better
Latency
Memory Latency in Nanoseconds (ns)
Shorter bars are better
The next step was 6GB in triple-channel mode, followed by 4GB of dual-channel memory and, finally, we tested with 4GB of single-channel memory. The winning set-up was 12GB of memory in triple-channel mode but it occurred to us that suspicion may be hanging over PCMark Vantage. We ran a final benchmark with Far Cry 2 and found that the 12GB and 6GB triple-channel systems had a modest advantage over the 4GB dual- and single-channel systems.
Far Cry 2 Results
Frames per Second (f/s)
Longer bars are better
Verdict
Stuff your 64-bit Core i7 system with 12GB of memory and you’ll reap the benefits.
Final Verdict
So there we have it: the Core i7's triple-channel memory controller shows little benefit over dual-channel but it doesn’t do any actual harm. Running astronomical memory speeds on Core i7 is a bit of a lost cause, and we recommend you stick to a maximum speed of 1333MHz, although the default 1066MHz speed works very nicely too. 12GB of memory works well but you’ll need a 64-bit operating system, and that's the real conclusion that we are taking away from all these days of testing. Don’t build a new Core i7 PC and run 32-bit software, but instead make the jump to 64-bit and pack it full of Ram. ®
Find the best prices for the memory we used
The best memory config for a Core i7 CPU
COMMENTS
@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.
@ AMD
Yes, I find it truly surprising that an 8-DIMM dual-opteron setup was not tested in this article for Core i7 memory configs!!
AMD
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 -
http://www.microsoft.com/whdc/system/platform/server/pae/paedrv.mspx
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.
http://tinyurl.com/n279v6
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.
Ian
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.
