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Single Channel Memory, AMD Zacate (Fusion) Question

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February 8, 2011 5:10:09 PM

I'm mapping out a low power bedroom HTPC build and at this time the AMD Fusion platform is where I'm headed.

For those who don't know, Fusion motherboards only support single channel memory (64-bit memory bus) and not the usual dual channel mode (128-bit memory bus). The Fusion board I am interested in has two DDR3 slots but since it does not add the benefit of dual channel when populating both slots, I am considering a single stick of 4GB RAM to keep power requirements to a minimum on this low power build.

So here is my question for the memory gurus:

Is it worthwhile to go for the fastest/low-latency stick of RAM the motherboard can take in an attempt to recoup some of the performance loss due to the single channel limitation?

For example, how would a stick of 4GB DDR3-1600 CAS7 RAM in single channel compare performance-wise to a DDR3-1066 or 1333 CAS9 2x2GB kit run in dual channel? What about 2x2GB DDR3-2000 or faster in single channel compared to a low-end kit in dual channel?

I'm also not convinced that a single stick of RAM is the way to go. Looking ahead, a 2-stick kit would be easier to transfer to another system that does support dual channel, or sell on fleabay. However, I'm looking to have the least amount of heat and power in my setup and I can't ignore that 2 sticks pulling ~1.5V each would not be as ideal as a single stick pulling half that. Additionally, for optimal heat dissipation one stick is better than two since the airflow is more restricted with two sticks in close proximity to one another. Comments on this matter are appreciated as well.

Thanks in advance.

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a c 229 } Memory
February 8, 2011 8:21:40 PM
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Borrowed from Wikipedia
"There have been varying reports as to the performance increase of dual-channel configurations, with some tests citing significant performance gains while others suggest almost no gain.

Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a "modern" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks.[3] Another comparison by laptoplogic.com resulted in a similar conclusion for integrated graphics.[4] The test results published by Tom's Hardware had a discrete graphics comparison.

The difference can be far more significant in applications that manipulate large amounts of data in memory. A comparison by TechConnect Magazine demonstrated considerable gains for dual-channel in tasks using block sizes greater than 4 MB, and during stream processing by the CPU"
My personal opinion, there is not going to be a noticeable difference in performance whether you have CAS 7 or 9 ram.
February 9, 2011 3:26:01 AM

OK, single and dual channel question solved. Any thought on the 1x4GB vs 2x2GB in respect to power savings/airflow? I might have a better selection of RAM if I go for 2 sticks since most are sold as kits. I'm waffling here...
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February 14, 2011 4:39:30 PM

I'd go with the 2X2GB. I'm building a similar setup and to me its more practical to have the 2X2GB memory. I'm often swapping and upgrading parts on various systems I maintain for my family.
February 15, 2011 2:50:40 PM

I think I've figured it out. I'll get a dual channel kit for my planned single channel HTPC so I have the option to transplant the memory into a future build if necessary. Hopefully DDR4 won't be the standard then!

Thanks all.
February 15, 2011 2:50:48 PM

Best answer selected by rwpritchett.
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