Dual vs. Quad Channel

The Mac Pro ships with two 512MB FB-DIMMs by default, which means that only two channels are populated. Moving to four FB-DIMMs allows you to have one FB-DIMM in each channel and thus get access to the full 21.3GB/s of bandwidth (in theory). So is there a performance difference between dual and quad channel memory configurations? We ran both configurations with the same amount of memory in all of our tests to find out:

For the most part, there's no benefit to having all four channels populated, but in some rare cases the performance boost can be tremendous. Given that lmbench showed us an increase in memory write speed when going from dual to quad channels, we can assume that the scenarios where we do see a large performance gain are write bandwidth bound.

If you're going to upgrade the memory in your Mac Pro anyways, you might as well stick to four FB-DIMMs as it will give you the best possible combination of latency and bandwidth (as good as you can get with FB-DIMMs that is).

Memory Performance Media Encoding Performance with iTunes and Quicktime
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  • plinden - Saturday, August 19, 2006 - link

    No point in arguing with this guy - he's shown just how much he knows about the subject. How could someone regularly read AnandTech and not know about EFI? And then profess to have confused it with some obscure mobo manufacturer?

    Oddly enough, I can't find any motherboards for sale manufactured by a company called EFI - either it's very obscure or he's making it up. I wonder which one it is?
  • michael2k - Friday, August 18, 2006 - link

    EFI isn't a manufacturer, it stands for "Extensible Firmware Interface", see the link in the other post.
    Lian Li had an aluminum case first, but Apple's design was COPIED by Lian Li. Read the Anandtech article in which half the comments for the case review claim "G5 ripoff".
  • plinden - Friday, August 18, 2006 - link


    EFI is an average/cheap mobo maker at best (not to say unreliable, just average in function, and performance). They are no DFI, or ASUS, not even close.

    I laughed out loud at this. You're absolutely right, EFI is no DFI or ASUS, not even close.

    You've just proved you know fuck all about this. I suggest you read up on EFI (http://en.wikipedia.org/wiki/Extensible_Firmware_I...">http://en.wikipedia.org/wiki/Extensible_Firmware_I... before posting about this in the future.

    I'm not going to tell you makes the Mac motherboards. I'll leave that up to you to research.
  • Petoschka - Wednesday, April 1, 2020 - link

    Well, my Junk Pro from early 2008 is still running.
  • pervisanathema - Wednesday, August 16, 2006 - link

    I want one. :o
  • takeshi7 - Tuesday, January 7, 2014 - link

    Just a small correction on page 2: The Power Mac G5 PCI-E also has 3 USB 2.0 ports on the rear panel.

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