Prices of low-voltage DDR 3 memory have dropped substantially as a result, and you can buy 3x1GB kits of 1066GHz DDR 3 for less than £30, while 3x2GB kits start at about £60. This is a significant dividing line as a 32-bit operating system can ‘only’ support 4GB of Ram, and you have to deduct the graphics memory from that amount. The result is that most PCs can support 2.5-3.5GB of memory with the result that most Core 2 and Phenom PCs typically have 2GB of Ram installed.
A Core i7 system running 32-bit software can have 3GB of Ram installed, which sounds as though it should be a step forward from 2GB.
On the other hand, if you step up to 64-bit Vista - or Windows 7 or Linux - you can install 6GB of Ram for £60. Most Core i7 motherboards have six memory slots - the exceptions that leap to mind are the Intel DX58SO with four slots and the latest Foxconn three-slot models - so you can install 12GB of DDR 3 in six modules for £120.
Faster DDR 3 is only slightly more expensive, with 3x2GB of 1600MHz DDR 3 available at a price of £80, while 2000MHz DDR 3 will take the cost past £100 for a 3x2GB kit. On the other hand, you can push the boat out and spend more than £250 for 3x2GB 2000MHz DDR 3, depending on the make and model that you choose.
We decided to take a closer look at how the memory that you choose affects the performance of a Core i7 PC and have tackled four main questions:
- What is the effect of the triple channel memory controller?
- How does memory speed affect Core i7 overclocking?
- What speed memory should you use to get the best from Core i7?
- What quantity of memory should you install in your Core i7 system?
Next page: How good is triple-channel memory?
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.
