Mac Pro RAM: Pairs? Please clarify

Discussion in 'Mac Pro' started by speekez, Jan 9, 2007.

  1. speekez macrumors 6502

    Nov 19, 2003
    Hi gang

    I'm going to be ordering a BTO Mac from Apple. I'll be using it for photo retouching & Aperture. I have read Aperture loves RAM and works best with 3-4 gigs of RAM. However, I don't want to spend the $$$ on expensive Mac RAM.

    My thought is to get the BTO with the stock Apple RAM configuration of 1 Gig (2 x 512MB) and then upgrade to 4gig total with third party RAM. My question is I heard the Mac Pro's should have RAM installed in matching dual pairs.... so, if I want 4Gig of RAM I should buy 4 x 1GB sticks so that I have two matching pairs, and then sell off the 2x512MB from Apple (because I shouldn't have 5GB in the computer?).

    Is this how it works? Or, could I keep the 2x512MB and match it with another pair of 2x512MB (third party). And then buy two more 1gig sticks?

    Any advice is appreciated!
  2. TheSpaz macrumors 604


    Jun 20, 2005
    You can keep the 2x512MB in your computer. 2x512MB is a matching pair. All the RAM pairs must come in the same size such as 2x1GB.

    You cannot however put 3x512MB in because 1 of those modules doesn't belong to a pair. Always install 2 modules at a time that are the same size. Since there's already 2x512MB in the Mac Pro, no need to take them out because they match.

    So finally to answer your question, there is no need to take out the existing matching 512MB set.

    Check out this diagram for all possible RAM configurations:
  3. adamyoshida macrumors regular

    Jul 10, 2006
    From your description, I'd recommend that you start out with three Gigs of ram.

    The problem with the MacPro's ram is that RDRAM, at the moment, is really, really, really expensive. I'd expect a big fall in prices PDQ.
  4. aaronw1986 macrumors 68030

    Oct 31, 2006
  5. eluk macrumors 6502a


    Dec 14, 2006
    East London, UK
  6. speekez thread starter macrumors 6502

    Nov 19, 2003
    Hi Spaz

    Thanks for the description and the diagram. Very helpful.

    Still, for optimum performace, apple still seems to encource "matching dual pairs"... (verses just matching pairs). Meaning if I put 2x1GB on Riser A, then I should put another 2x1GB on Riser B (matching dual pairs). I think somehow this helps the MacPro take full advantage of double memory bandwidth, 256bit .... Some of the configurations in the diagram don't adhere to this rule -- that's not to say that some of the configurations in the diagram won't work, but they might not allow for optimum performance.

    See Apple Doc below:
  7. djray77 macrumors newbie

    Jan 10, 2007
    Well I just got my macpro tuesday (man these are great machine btw) and it came with 2gb. If I wanted to put another 2gb in would I have to buy 4x512mb sticks? or could I just buy 2x1gb sticks? Sorry Im new to macs and want to make sure I have this right :)
  8. Silentwave macrumors 68000

    May 26, 2006
    Gainesville, FL
    The Mac Pro doesn't use RDRAM- it uses DDR2 667 FB-DIMM SDRAM. Prices on this are not likely to fall very much in the near future because it is a very small market and has high tolerances.
  9. eMagine macrumors regular


    Sep 18, 2006
    Los Angeles, CA

    you're on the right track...
  10. PmattF macrumors member

    Dec 28, 2006
    That is very interesting, especially because it conflicts with this official Apple document, which explicitly says you do not need dual pairs, just pairs...
  11. dkoralek macrumors 6502


    Sep 12, 2006
    I believe that you are mistaking what you need to do vs. what is optimum. You only _need_ pairs. But if you want to be able to access memory using full quad channel you need two pairs (one on each riser), and my guess is that having four of the same size and speed will give the best performance of all. That said, a lot of examples out there show that there isn't that great a performance gain by doing this (particularly if the decision is four dims or six which result in more RAM).

  12. Sun Baked macrumors G5

    Sun Baked

    May 19, 2002
    The memory requires pairs due to the dual channel operation (Using dual channel Branch 0 or 1), however adding 4x(matched DIMMs) will run it in the optional quad channel mode if the DIMMs are in the same slots on two risers (This uses Branch 0 and 1 at the same time).

    However only 4 DIMMs operate/(are active) at once (all the slot 1-2 or 3-4 DIMMs) -- before switching to (looking at) the other DIMMs.

  13. TheSpaz macrumors 604


    Jun 20, 2005
  14. PmattF macrumors member

    Dec 28, 2006
    This page says you get quad channel performance simply by installing matched pairs, does not say the pairs have to be matched from each other...

    However, this page, from a later article, if I am reading it correctly, says that ideally all devices should be "dual rank", meaning 1 gig or 2 gig pieces. Which again does not say that pairs have to match each other, but does seem to imply that you would not want to use 512's (as comes from Apple with the base configuration)...
  15. TheSpaz macrumors 604


    Jun 20, 2005
    Here's a new question:

    What would be the better value:
    1.) Getting one more 2x512MB set and running Quad-Channel (total of 2GB)
    2.) Getting one 2x1GB set and running only Dual-Channel (total of 3GB)
  16. slughead macrumors 68040


    Apr 28, 2004
    How many times do I have to point this out:


    It's PROVEN. Come on guys, quit suckin down the hype.

    So to get 4GB, take the stock 1 and add two 512's and two 1GB's. FIN!
    We ran some typical tests from our suite of real world tests (iMovie render effect, Final Cut Pro render clip, Cinebench CPU render, Motion render RAM preview, iMaginator Core Image morph). None of them showed any gains from Quad Channel mode.
  17. PmattF macrumors member

    Dec 28, 2006
    This article shows that in fact there is a real (though not huge) performance gain from quad channel vs. dual channel...

    But that point is moot anyway, as you get quad channel simply by populating both risers, so the configuration you suggest is in fact quad channel.

    I still have not seen any actual tests on whether using symmetrical pairs across the risers and/or avoid "single rank" 512 modules actually makes a measurable difference.

    I do suspect that you are correct -- 4x512 plus 2x1gig would not be noticeably different in any way from 4x1gig. But still, I would love to see somebody actually test this.
  18. PmattF macrumors member

    Dec 28, 2006
    Or actually, in the 4x512 + 2x1 gig scenario (i.e. in the second configuration on the 4gb row) maybe only the first three gig would be running in quad channel, and the last gig, would be dual channel?
  19. TheSpaz macrumors 604


    Jun 20, 2005
    I have a headache. I'm just gonna get the 2x1GB for right now and wait to add more when the prices are normalified.
  20. speedfreak macrumors newbie

    Jan 11, 2007
    The Netherlands
    you're not the only one with a headache. I'm also 1 newly Mac Pro user with the same question. Got a standaard Mac Pro and want to add 4gig of memory. Should I get 2x2gig+the standard 2x512mb or 4x1gig+the standard 2x512mb??
  21. speekez thread starter macrumors 6502

    Nov 19, 2003
    I have decided on 4 gigs of RAM. I am configuring a built to order and, including the prices for OWC RAM, I have found that the cheapest road to 4GB is as follows:

    1. Order the stock 1GB (2x512MB) from Apple when you configure your Mac Pro. I qualify for education discount, so my total below reflects this.

    2. Order another gig (2x512MB) from OWC for $219

    3. Order another 2 gigs (2x1GB) from OWC for $399

    Total (assuming you are ordering from Apple with an education discount) is $618. And, you have 2 slots left over.

    If you order 4x512MB from Apple when configuring and the 2x1GB from OWC, the total is $668

    I have not looked at other third party RAM yet -- so there may even be cheaper options than OWC.

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