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I have a Hp 630 laptop. 2 DIMMs and 2GB(1066 Mhz) of ram on one slot. I want to upgrade it.

At this point I have two solutions:

  1. upgrade to 4gb (2x2 Gb)
  2. upgrade to 6gb (1x2 Gb + 1x4 Gb)

Which one is better?

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What operating system? (Be as complete as possible.) –  David Schwartz Nov 20 '11 at 19:40
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@David you don't really need to know if your upgrading RAM... –  Simon Sheehan Nov 20 '11 at 20:43
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@SimonSheehan Really? So your answer would be the same if he's running Windows XP 32-bit as it would be if he was running 64-bit Linux? –  David Schwartz Nov 20 '11 at 21:26
    
@David he's asking about performance: OS is a whole other story. –  Simon Sheehan Nov 20 '11 at 21:30
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@SimonSheehan If his OS can only use 4GB, then the 4GB will perform better because it will give him dual-channel. If his OS is 64-bit, the 6GB will likely perform better because 50% more RAM will probably improve performance more than losing dual-channel will hurt it. You cannot give a good answer to this question without knowing the OS. –  David Schwartz Nov 20 '11 at 21:32
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2 Answers

Performance advantage of dual-channel configurations is negligible in most workloads -- on the order of 1 to 5 percent. (See, for example, http://www.tomshardware.com/reviews/PARALLEL-PROCESSING,1705-11.html.)

Once you hit swap, however, you will be penalized by orders of magnitude. 100 MB/s vs 8000 MB/s. I would always choose more RAM.

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I vote for the 6gb version. Why? I have 4gb in my laptop, with a Windows 7 Professional x64. Sometimes I get near to 3.7gb of usage. Only using browsers, and a lot of background stuff. (Skype, MSN, etc.) Mostly the browser will eat the rest. Why I wouldn't care about the speed? Because I have never seen a difference. I've had SDRAM. I've had DDR2 533-800. DDR3 1066-1600mhz. No difference. Maybe, in numbers. Or in a benchmark. But in user experience? NONE. –  Shiki Nov 20 '11 at 21:14
    
Agreed, most real world benchmarks show very little impact when increasing ram speed. It's surprising, but speaks to the fact that RAM bandwidth is already so fast that it is rarely the bottleneck. –  AaronLS Aug 6 '12 at 22:57
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2x2GB will allow your system to work in full dual-channel mode, which means that memory transfers will be faster.

Depending on your processor you may be able to use a hybrid dual channel mode (on Intel i-series processors) which gives the best of both worlds, but means that above 4GB of used RAM you will not see the speed benefit of dual channel.I do not know if AMD processors support this extra mode

If you often find yourself running out of RAM then the 6GB configuration may be better for you, if not then the dual-channel mode will give better performance.

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