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Re: Memory copy performance on G5

When I say copy bandwidth, I am following what STREAM benchmark does, copy bandwidth= read bandwidth + write bandwidth.  So the 3.1 GB/s copy bandwidth means 1.55 GB/s read bandwidth and 1.55 GB/s write bandwidth.

I believe the 1Ghz front bus means 8GB/s theoretical FSB bandwidth. And the 400 Mhz double-pumped memory bus means 400x2x8 = 6400MB/s = 6.4 GB/s bandwidth.

I am using a dual-proc machine and only 1 proc is used. I don't think it should be a problem. I still have no clue why I only got 3.1 GB/s. Anyone can try this on his own G5?

Thanks!

Best,
QD


On 11/7/05, Rob Barris <email@hidden> wrote:

     The G5 memory controller is dual channel though.  There's 6.4GB/
s available at the memory pins - but at 1GHz FSB the max read speed
at the CPU side is going to be 3.2GB/s or slightly less.  If you are
able to copy 3.2GB/s or somewhere in that ball park, you're getting
close to "speed of light" with it.

     A "perfect" memory controller would not be able to copy more
than 3.2GB/s using a 6.4GB/s memory subsystem since the memory can't
read and write simultaneously.

Rob

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References: 
 >Memory copy performance on G5 (From: Qingda Lu <email@hidden>)
 >Re: Memory copy performance on G5 (From: Jonas Maebe <email@hidden>)
 >Re: Memory copy performance on G5 (From: Rob Barris <email@hidden>)



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