New Mac Pro Memory: 3x2GB or 2x1GB+2x2GB?

Discussion in 'Mac Pro' started by neiltc13, May 2, 2009.

  1. neiltc13 macrumors 68040

    neiltc13

    Joined:
    May 27, 2006
    #1
    This has probably already been addressed, but tried searching and found nothing. Anyway, my question is this:

    I've ordered the quad core 2.66GHz model and it will be delivered next week. As I understand it, the computer ships with 4 memory slots, three of which are occupied with 1GB modules.

    I'm not sure about the triple channel memory though - as I understand it, this means that the computer works best when the memory installed is a multiple of 3, so 3GB, 6GB, 9GB, 12GB etc.

    But what I am wondering is if you have to install matching memory to get best performance. What I would like to do is remove one of the 1GB sticks which is coming with my Mac Pro and add two 2GB sticks.

    This would mean that I would have 4 full RAM slots, two with 2GB in and two with 1GB in them, leaving a total of 6GB.

    The reason I ask is that it is much cheaper to do this than to buy a whole new set of 2GB DIMMs to fill up three slots. Has anyone tried this or know whether it's the best idea?
     
  2. chelsel macrumors 6502

    Joined:
    May 24, 2007
    #2
    the sticks have to be the same type, size and speed. You'll probably want to buy from someone like OWC which will give you a rebate for sending in your "old" memory (3x1gb).

    Also, the performance increase is negligible when running in "triple channel" compared to the performance increase you get from the extra RAM, based on what I've read.
     
  3. neiltc13 thread starter macrumors 68040

    neiltc13

    Joined:
    May 27, 2006
    #3
    Well I'm not going to import memory from abroad, the best price I've found so far is with Crucial who the 3x2GB for about £100, which just happens to be the same sort of price Apple wanted to put the memory into my machine themselves.

    I didn't realise they had to be the same size - the Mac Pro user guide doesn't say they have to be.
     
  4. VirtualRain macrumors 603

    VirtualRain

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    #4
    I don't think they have to be the same size but if you want the full benefits of triple channel performance, the first three sticks have to be the same size.
     
  5. Tesselator macrumors 601

    Tesselator

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    #5
    I think it's smarter than that yet. I believe that if you put 2GB, 2GB, 1GB modules into the system then your 1st 3 gigs of system memory will be addressed at triple channel speeds. The remaining 2 gigs will get dual channel access.
     
  6. 3587 macrumors 6502a

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    Mar 23, 2008
    #6
    Just do what I did with my 2.66... 4X2GB and be done with it! I read an article where it was like .01 off! So basically no difference between 6GB and 8GB as far as speed goes... 6 vs 8 when it comes to running programs, now were talking! More MEMORY is always better!
     
  7. Roy macrumors 6502

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    Jul 6, 2006
    #7
    Or if he just buys one 2GB and places it in the 4th slot, then the 1GB modules in slot 1, 2, 3 will run as triple channel speeds and the the 2GB in the 4th slot runs as what or how?
     
  8. ReanimationLP macrumors 68030

    ReanimationLP

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    #8
    When you have an even number of RAM in your machine, it will run in Dual Channel, not Triple Channel.

    This goes for all i7-based systems, which the Mac Pro is based off of.
     
  9. VirtualRain macrumors 603

    VirtualRain

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    #9
    The Intel documentation is vague but one interpretation is that if the memory controller detects a non-symmetrical memory configuration across the three channels, it may default to dual-channel mode. Hence it would be safest to use three and only three identical sticks to ensure maximum memory performance.
     
  10. Roy macrumors 6502

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    Jul 6, 2006
    #10
    Not disagreeing with your statement, but look at what Apple offers. Apple gives the option of filling all 4 slots and even goes on to give a reason why it is best to have as much memory as possible (even including all 4 slots, as by giving this as an option and by including a 4th slot rather than offering just 3 slots or multiples of 3 in the Octo case.)
    • 8GB (4x2GB) [Add $250.00]
    The quad-core Mac Pro supports up to 8GB of 1066MHz DDR3 ECC SDRAM memory in four slots. Choose more memory for improved overall system performance.

    Because accessing data from memory is much faster than accessing data from the hard drive, the more memory your system has, the faster it can manipulate your data. The result is greater application performance, especially when working with large files and memory-intensive applications such as graphics, audio, video, and scientific applications.
     
  11. Tesselator macrumors 601

    Tesselator

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    #11
    Point taken. Thanks.


    Yeah, but that doesn't really apply to this part of the discussion. And in many cases it's not actually true. For example going from 12GB to 16GB is going to be slower in MANY more cases then not if it means you're dropping down from triple-channel to dual-channel access modes. Alternatively it will be the opposite if all you have is 3GB and you upgrade to 16GB where the larger amount of memory will speed up applications which before were hitting the drive cache.

    The best case is to get a large amount of RAM which is also accessed in triple channel mode. :)
     
  12. Roy macrumors 6502

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    Jul 6, 2006
    #12
    And that's the reason I keep watching the 4GB memory modules slowly drop in price. :)

    The best I can remember, when I first started mentally tracking these, was that 12GB (4GB modules 3X4) was $750. So it's down about $120 in about 2 months.

    [​IMG] 12.0GB OWC Matched Set (4GB x 3) PC-8500 1066MHz DDR3 E... $629.99
     
  13. TheSpaz macrumors 604

    TheSpaz

    Joined:
    Jun 20, 2005
    #13
    My first generation Mac Pro has 8 slots. I have 5GB of RAM. How many channels am I running? I'm confused.
     
  14. neiltc13 thread starter macrumors 68040

    neiltc13

    Joined:
    May 27, 2006
    #14
    Thanks for the replies everyone. I really don't think I need 6GB RAM, and from the way you are describing things I think my best bet will be to simply fill up the fourth slot with another 1GB stick.

    Looks like Crucial sell them for about £20. Alternatively, I could add a 2GB stick which is about £30.

    What do you guys think is the best idea? I'm a web designer who loves gaming.
     

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