Best amount of RAM in a Nehalem Mac Pro?

Discussion in 'Mac Pro' started by jjahshik32, Aug 19, 2009.

  1. jjahshik32 macrumors 603

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    Sep 4, 2006
    #1
    I'm torn between 12GB vs. 16GB. If I buy the 8x2GB its so much cheaper but does this mean that triple channel wont be used?

    I've read somewhere on these threads (an older thread from googling) that the if the first 3 RAM slots match (in this case 2GB dimms) then it should enable tripple channel + the rest 2 should be used as single. Is this true?

    If so then I should just get the 8x2GB configuration.
     
  2. designed macrumors 6502

    designed

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    #2
    I presume you're talking about the 8-core MP with 8 slots, in which case the best configuration (channel-wise) is to go with 6 memory modules. It gives you the triple channel mode.

    Then again, if you really do need the additional 4 GB of RAM, then go with 8x2.
     
  3. lemonade-maker macrumors 6502

    lemonade-maker

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    Jun 20, 2009
    #3
    fill it up. you wont know the diff between 16 and 12.
     
  4. alphaod macrumors Core

    alphaod

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    #4
    I feel 12GB is plenty and I'm the one always complaining about not-enough RAM.

    I'd just get the 12GB and later down the line if you need it, you can always at the 2 additional modules.

    I don't really know what you mean when you say 8x2GB is cheaper; if it is, then buy that and still just install 6x2GB to see if it suits your needs and if not, install the additional sticks.
     
  5. matthewtoney macrumors regular

    matthewtoney

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    Charlotte, NC
    #5
    3 X 4gb

    I just order 12GB (3 X 4GB) from Newegg for mine, but I have the quad-core so I had no choice about it really for going over 8GB. I got it for $339 which seems pretty good to me for the 4GB sticks - I'll post here when it arrives how it works if anyone wants.

    http://www.newegg.com/Product/Product.aspx?Item=N82E16820220408
     
  6. jjahshik32 thread starter macrumors 603

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    #6
    I just decided on 4x4gb for now for a total of 16GB and in the future I'll add another 4x4gb for a total of 32GB. :D
     
  7. VirtualRain macrumors 603

    VirtualRain

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    #7
    The best amount of RAM for a 2009 Mac Pro is the greater of:
    - A multiple of 3 DIMMS (Quad) or 6 DIMMS (Octo)
    - What you need to avoid page-outs

    It's more important to have enough memory than top performing memory, but it's ideal to have both.
     
  8. alphaod macrumors Core

    alphaod

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    #8
    That works. :p
     
  9. cmwade77 macrumors 6502a

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    #9
    I would actually buy it with as little RAM as possible, then upgrade the RAM yourself, this will save a substantial amount of money, as Apple way overcharges for the RAM
     
  10. VirtualRain macrumors 603

    VirtualRain

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    #10
    That's a smokin deal... let me know how it works out... I will likely do the same! :D

    EDIT: It doesn't mention a thermal sensor, which I thought is a requirement for the Mac Pro?
     
  11. jjahshik32 thread starter macrumors 603

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    Sep 4, 2006
    #11
    I always buy my Mac Pro's RAM from transintl.com I think their RAM is of high quality.

    Anyway, anyone know if I mix in the 1GB DIMMS in with the 4GB? I think I've read that you cant because after I put in the 4x4GB I'd like to fill in the rest with 1GB.
     
  12. Cynicalone macrumors 68040

    Cynicalone

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    #12
    Page outs is kinda a funny thing I still get them with 32GB of RAM. 32-bit software is more of a problem than a lack of RAM for me. The 64-bit era can't come soon enough.
     
  13. matthewtoney macrumors regular

    matthewtoney

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    #13
    My understanding (which could be mistaken) is that at least as of a couple of years ago, using DIMMs without a thermal sensor would work fine, but would cause the Mac Pro to run the fans (not sure which or if all) at full speed all the time. I have no idea whether or not that is still the case, or whether or not those DIMMs I order have a thermal sensor or not (although as you mentioned they don't say anything about it) but I guess I'll find out! :)
     
  14. XandeR803 macrumors member

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    Jul 25, 2008
    #14
    Do keep us updated. If they work well (without constant full speed fan), I would purchase the same ones for my quad.
     
  15. Boneoh macrumors 6502

    Boneoh

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    #15
  16. matthewtoney macrumors regular

    matthewtoney

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    #16
    New RAM

    Well I've got them now and they're in my 2009 Mac Pro Quad - they work great and the fan speeds haven't changed at all - don't know whether or not that's because these things really do have a thermal sensor, or just that with the 2009 Mac Pro models perhaps the full-speed-fan stuff doesn't happen anymore. Regardless, I can easily recommend that $339 deal now from Newegg for 3 matched-pair 4GB sticks.
     
  17. dekka007 macrumors member

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    Jun 6, 2009
    #17
  18. Umbongo macrumors 601

    Umbongo

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    #18
    I'm interested to know how you have your memory arranged.

    The best choice is probably having two 4GB DIMMs for each processor as you'd get more perfromance stability that way. About 75% of the performance youd see if both had 3 DIMMs.
     
  19. matthewtoney macrumors regular

    matthewtoney

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    #19
    I believe those would work just as well, although like you say they would run at the 1066mhz speed and not the rate 1333mhz
     
  20. VirtualRain macrumors 603

    VirtualRain

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    #20
    Sweet... that's great! :D

    Right. Sounds like a good choice as well... except the CAS rating is 9 vs 7 for the others. However, the SPD may be programmed for 1066 CAS7 on these anyway, although CAS8 is more likely. Unfortunately, you won't know until you try if the lower timings will appear. If you try these, please report back with your findings. If you can return them, there's no harm in trying.
     
  21. nanofrog macrumors G4

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    May 6, 2008
    #21
    Is there a utility for OS X that allows a user to set the CAS timing data in EFI ('09 model of course)?
     
  22. VirtualRain macrumors 603

    VirtualRain

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    #22
    No. Not that I'm aware of.

    I was supposing that the memory SPD table might be programmed with a range of speeds and CAS timings. For example, memory rated for 1333 at CAS9 may also have an entry in the table for other JEDEC speeds such as 1066 at CAS8, but that assumes the memory passed QC at CAS8 at 1066. No way to know what the SPD is programmed with until you fire it up.

    As far as verifying what the CAS is, I'm not even sure there is a utility for OSX that will read the SPD or EFI... is there? If not, then you will have to use CPUZ under Windows to see what's going on.
     
  23. nanofrog macrumors G4

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    May 6, 2008
    #23
    I'm not aware of any utility similar to CPU-Z for OS X, nor was I sure that the system could be manually adjusted or not (SPD table).

    A utility would be easier, but so long as a manual means is possible, whom ever figures it out can post the proceedure to assist others that want to do this as well. :) Options are nice. ;)
     
  24. AZREOSpecialist macrumors 68000

    AZREOSpecialist

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    Mar 15, 2009
    #24
    For the vast majority of users, the difference between populating 3 memory slots vs. 4 will not result in a discernible performance difference. Most benchmarks appear to point to a 3-5% RAM performance penalty when you go to 4/8 DIMMs, which is not something anyone really needs to worry about. For those who want that 3-5% RAM performance back while using 4 DIMMs can replace their Quad Xeon with an equivalent Core i7 processor without ECC support. You get back that 3-5% performance when you don't have ECC overhead to deal with.
     
  25. nanofrog macrumors G4

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    May 6, 2008
    #25
    Odd way to go about it, but it would work. :p

    ECC's overhead isn't much to worry about anyway, and most usage does just fine in dual channel mode, which is what the system falls back to when you populate the 4th DIMM per processor. Unless the system is a server, not really anything to worry about right now. Down the road, maybe, assuming the software catches up before the machine is too old to serve it's current purpose. ;)
     

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