Building an Intel Core i7 based computer – Memory

Core i7 requires DDR3 memory. The more cheaper and slower DDR2 isn’t an option. But beware that not every DDR3 memory is good for Core i7. Oh no, they have to have a lower voltage than usual, that’s max 1.65V (1.5V recommended). Lookout for memory modules that are “build/optimized/etc. for Core i7”. Read this article to learn more about differences between DDR2 and DDR3.

Another innovation in memory access is that Core i7 is capable of using three channels to read/write from/to memory. Previous Intel and AMD CPUs could utilize only two channels at most. Thus the necessity for a triple channel modules. IOW you get the best performance by using three (or a multiplier of) physical modules. You are not constrained by the multiplier of three (the number of modules depends on motherboard as well – not every motherboard accepts many modules) but then you’ll get lower performances.

So, I’ll go for three DDR3 modules.

The final two aspects of interests to me where I can choose:

  • size
    I’ve chosen the size of 6GB (3x2GB) because I think it will be enough for my usage. Note that you shouldn’t go below your requirements (you should know how much memory on average your applications consume and what applications you are going to run at the same time) – if you run out of physical memory then your computer will start swapping memory to disk like crazy and performance will go down the drain. So, the size matters after all. No need for exaggeration though. Having more memory than required doesn’t help a lot.

    Another word of caution: 32 bit operating systems can’t use more than, at most, 3.5GB of RAM (there are ways for servers to get around this limitation but for special use). This is a hardware limitation. Which means that if you want to use more than 3.5GB of RAM you’ll have to install a 64 bit OS which doesn’t have such a limitation. In fact I am planning to install either Windows 7 x64 or Vista x64.

  • performance/price and performance
    The faster the memory is, the faster can CPU access it and thus your applications will run faster.
    There are two factors affecting memory performance: frequency and latency. The former should be as high as possible (1333 is the lowest and cheapest frequency for DDR3 that I’ve found on the net – note: allowed max and min frequency depends on the motherboard as well) but then again, not too high because of a non-linear increase of performance/price – you don’t gain that much performance if you increase the frequency insanely. Also beware that there are two frequency labels out there: one is the frequency itself (i.e. 1600Mhz) while the other is a PC3 rating that depends on the frequency (PC3 12700 for 1600Mhz).
    The other factor is latency. It is marked by a single number (i.e. CL9) or by a group of numbers where first number is CL (i.e. 9-9-9-27). The number(s) should be as low as possible because latency (simplified) states how much time is required for memory module to do an operation.
    Memory frequency is far more important than latency (look at the benchmark tests on the web). Thus invest in higher frequencies rather than lower latency. Or better, both, but the most important is frequency.
    After a while I concluded that I’ll go for a 1600Mhz/CL9 modules, partially because of price and partially because of the lack of the availability of lower latency 1600Mhz modules – I was shooting for CL7 but I couldn’t find any (OCZ has nice modules for a great price – but those can’t be found these days).

I bought a Super Talent 6GB/DDR3/1600/CL9 triple channel kit (SKU: WA160UX6G9) modules from Mlacom for 238 Euros.


See other relevant posts:

CPU cooler
The goal
Power Supply Unit

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