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I've heard and read online that some CPUs (or motherboards?) perform better with a certain number of memory (3,6,9 as opposed to 2,4,8). How do I know what is the best for each PC/Laptop configuration?

Also, does the number of sticks matter? Right now i have 3 sticks in my Lenovo Thinkpad W520 with Intel iCore 7: 4gb, 2gb, and 4gb

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Have you done the obvious and checked the manual? The manuals usually tell you what the system is designed for. –  Zoredache Aug 18 '11 at 0:09

2 Answers 2

The actual total capacity you need depends on the applications and operating system you are going to use. They normally does not affect the speed of the system apart from the simply fact that more memory means less paging and faster response. For a typical computer today running a 64-bit OS, you need 4GB of RAM.

The configuration of the sticks slightly (marginally?) affects the speed of the memory sub-system. The exact requirements are mother-board specific, but the general rule is you need an even number of sticks that are exactly the same to use dual-channel.

Some motherboard/BIOS allows you to use different ones, but many laptop don't. So you need RAMs that have the same capacity, speed and bank configuration (i.e. how the chips are grouped). Some motherboard can enable dual-channel with a single dual-bank RAM, but I won't count on that.

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Ahh, way way back in the days of the first Athlons and Athlon II, dual channeling(which required an even number of memory modules) provided large gains in performance. But back then, it was easy to make your CPU sweat.

All laptops these days support async dual channeling. In layman's terms, the number of memory modules won't matter except for one instance.

The more modules you have, the better. And that's it.

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