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A7V880 and so called dual channel memory access
I have a Sempron 2600+ plugged into an A7V880. It's a 333MHz FSB
system, rather than a 400 MHz, and I have two Kinston 256 MB DIMMs--in the blue slots just as it suggests to. When it boots, the BIOS does tell me it is in Dual Channel mode. In the BIOS you can turn on or off dual channel memory access. What is interesting is that according to the Sandra benchmark the memory bandwidth numbers REMAIN NEARLY IDENTICAL whether dual channel memory is enabled or disabled. Int = 2261MB, Float 2100. Also, if you take a look at Kingston's site there is a PDF whitepaper on Intel's dual channel memory information, and one graphic is a chart that outlines the different bandwidths of different types of memory in GB/sec. DDR333 peaks at 5.4GB/sec. No real world results seem to measure up to the theoretical limit, including all the Intel CPU/chipset combos, and I'm just curious why. I'm most curious as to why there is no difference in performance on the board I have when dual channel memory is off--it's one of the reasons I bought the board. Dave in Colorado |
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Pretty cool, eh :-) Makes you wonder why they put dual channel on
the Athlon motherboards. The deal is all in the numbers. Both the Athlon and the P4 have a 64 bit data bus. The Athlon is a DDR bus, and the P4 is a QDR (quad pumped) bus. If the Athlon is clocked at 200MHz, there are 400Megatransfers per second, or 3200MB/sec. That bandwidth is obviously fully matched by a single DDR DIMM running at PC3200, clocked at 200MHz for a DDR400 transfer rate. The P4 is quad pumped, and with a 200MHz clock, has 800Megatransfer per second. With the same 64 bit bus width, that gives 6.4GB/sec transfer rate. That is fully met by two PC3200 DIMMs running in dual channel (Uber DIMM) mode. Thanks, Paul, for a great explanation! Another question/observation if I may. As I understand it, at any given moment, the CPU (depending on its size and the job at hand) actually has in it's L1 or L2 cache approximately 90% of what it needs to do its job. I don't recall how many times or where I've learned that. Perhaps it isn't true. I don't know. If it's true, doubling RAM speed actually might make a difference in performance of half of the rest--half of 10%. What I do know is this: I've got at work both a P4 2000 (400 MHz FSB) and I've got an Athlon 2000+ on a 133MHz FSB. With equal RAM, OS and some of the fastest hard disks as of a year ago--the WD WD800JB 8MB cache model I found very similar performance while compiling/building a large Visual Studio .NET 2003 project (I followed identical OS and software procedures.) They both took between 12 and 13 minutes to build the project, and CPU use hovered at around 95 percent during the builds on both of them. I don't even remember specifically which was faster at the moment--I just remember thinking that it really was not very significant, and that's with the P4 also having the benefit of 2X the cache. My point is that in this particular real world application that is extremely CPU and RAM intensive, high tech high speed RAM and high FSB chipset essentially meant nothing, and the AMD CPU was half the price. I feel like I'm missing something here. Dave in Colorado |
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