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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  • DigitalFreak - Wednesday, August 16, 2006 - link

    Is there a 64bit version of OS X for the Intel platform? I didn't think there was, considering that until now all of the Intel Macs have only had 32bit processors.
  • kelmon - Thursday, August 17, 2006 - link

    Depends on what you mean by 64-bit. OS X has, I believe, had a 64-bit UNIX layer since 10.3 (I don't think it was introduced with 10.4) but the only applications that can take advantage of this are command-line tools. Leopard will introduce 64-bit everywhere but I'm still struggling to find a reason why that will impact me in a good way. That said, the new Mac will have a 64-bit processor so that I can feel future-proof.
  • Pirks - Wednesday, August 16, 2006 - link


    Is there a 64bit version of OS X for the Intel platform?
    Good question. I don't know, maybe OS X on those Mac Pros is patched to 64-bit or something.. if not than I should shut up and wait till Leopard.
  • Snuffalufagus - Wednesday, August 16, 2006 - link

    it should factor in at least a 25% - 35% discount code on the Dell :).

    I have never bought anything off the Dell site without getting a substantial discount from a current promotion.
  • trivik12 - Wednesday, August 16, 2006 - link

    Does Dell offer 25-35% off for Dell Precision Workstation?
  • MrPIppy - Wednesday, August 16, 2006 - link

    The last generation of Power Mac G5s also had dual GigE ports: http://www.apple.com/powermac/specs.html">Apple's G5 specs page

    One difference though, the G5s (and the GigE G4s before them) used Broadcom 57xx chips for Ethernet, while the Mac Pro now uses an Intel 8254x chip.
  • Josh7289 - Wednesday, August 16, 2006 - link

    But what is so good about Macs? Why would I want a Mac instead of a PC? What can a Mac offer me that a PC can't? I don't like trolling, but I seriously am asking these questions and want to know what the answers are.
  • phaxmohdem - Wednesday, August 16, 2006 - link

    I used to be a mac hater because All the macs I've ever used truely were Pieces of $h!t. Old single cpu G4 towers with no Hard Drive Space or RAM, and way too much student crap spread on them. HOWEVER recently I had the pleasure of using a REAL mac (Quad G5) for a video project, and it made me think of macs a little differently. Plenty fast, and stable. My biggest problems were learning all the new Mac hot keys and keyboard shortcuts.. but once you master those you'll fly on the mac. (Some of Macs shortcuts still seem pretty stupid and complex to me though).

    However I serioualy don't understand the keyboard and mouse that Apple gives their cusotomers... The new mighty mouse is an improvement, but still an uncomfortable POS to me. Ditto for the mushy fugly keyboard that is standard. I've found that a proper Logitech (or similar) Kybd/Mouse combo makes the mac experience feel 10x better. (One more side-gripe... OS X does not have adjustments for mouse acceleration, and for me the stock acceleration speeds are wretched and piss me off... Hopefully this is something to be updated in the next release of the OS)

    So, moral of my story is... if you're going to Mac it up, do it right with proper input devices and some decent specs, and you'll have an enjoyable experience under OS X. I personally still choose Windows for its versatility w/ software and hardware... but to each his own.
  • Maury Markowitz - Thursday, August 17, 2006 - link

    Agree. I find it somewhat ironic that the only MS products I really like are their keyboards, mice, and joysticks. What's particularily maddening is that Apple used to, years ago, make the best keyboard money could buy. Seriously, solid as a rock and typing feel you'd kill for. Now they peddle crap that looks nice. Not good.
  • timelag - Thursday, August 17, 2006 - link

    Apple used to, years ago, make the best keyboard money could buy.

    Ah yes, the extended keyboard II. Better even than the famous IBM and Sun keyboards of yore. If it weren't for my Kinesis (the One True ergo keyboard), I'd be using mine through an ADB to USB connector.

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