1 16GB of RAM vs 3 4GB of RAM

Discussion in 'Mac Pro' started by gissentml, Nov 7, 2014.

  1. gissentml macrumors newbie

    Joined:
    Sep 21, 2010
    #1
    I just ordered a bone stock Mac Pro 2013 and I am curious to know if I am hindering performance by removing the 3 4GB units of ram and purchasing a single 16GB of ram module.
     
  2. Korican100 macrumors 6502a

    Korican100

    Joined:
    Oct 9, 2012
    #2
    Sorry man I don't believe it works that way. As a matter of fact, if you don't occupy at least 2 slots, the new Mac pro doesn't even start. At least that's what a applestore person told me when I asked the same question.
     
  3. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #3
    Thats was the case back with the old models prior to 2009, when they had to have matched pairs of memory. That isn't how it works now.
     
  4. Korican100 macrumors 6502a

    Korican100

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    Oct 9, 2012
    #4
    But it does hinder performance though
     
  5. Umbongo macrumors 601

    Umbongo

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    Sep 14, 2006
    Location:
    England
    #5
    Eh, not really. Single channel vs. triple channel isn't massively different for most use. I assume you want to buy a single 16GB so you can upgrading the future, but unless you plan on absolutely doing it very soon I really wouldn't bother. Do you know you need more than 12GB? More than 16GB in the future? Unless you are coming from 16GB already I'd get another 4GB and see how you go.

    ----------

    You'd be pressed to notice it. You can see it in memory benchmarks, I've seen it with RAM disk performance and some of the other memory heavy stuff I do, but it wouldn't concern me if I were going to get another 16GB DIMM in a few months and money was tight. Capacity is king.
     
  6. flowrider macrumors 601

    flowrider

    Joined:
    Nov 23, 2012
    #6
    Apple doesn't say not to, but their recommendation is mute on whether or not only one DIMM in one slot will work or not. They only say don't mix RDIMM and UDIMM.

    http://support.apple.com/en-us/HT6054

    Lou
     
  7. gissentml thread starter macrumors newbie

    Joined:
    Sep 21, 2010
    #7
    my whole purpose of moving to one 16GB is so that as funds become available and I need to upgrade I can add 16GB at a time. Adding 4GB right now is only $75. However, OWC allows me to trade in my 3 4GB sticks at about 25 each so I would essentially be paying $125 for 16GB but I have 3 open slots for later.
     
  8. h9826790 macrumors G3

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #8
    Not a good deal for me.

    1) You pay extra $50 (66%) for the same amount of working RAM.

    2) you lost the stock RAM as the backup.

    3) there are 4 channels there but you only utilise one. 75% of resource sits there and doing nothing but only standby for possible future use.
     
  9. ToroidalZeus macrumors 68020

    ToroidalZeus

    Joined:
    Dec 8, 2009
    #9
    unless you are changing the frequency just run all 4 sticks.
     
  10. AidenShaw macrumors P6

    AidenShaw

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    Feb 8, 2003
    Location:
    The Peninsula
    #10
    This thread has a lot of info about performance of different memory configs:

    http://forums.macrumors.com/showthread.php?t=1704700

    To summarize, most applications are happy with the large caches on the E5-x6xx v2 CPUs and don't see much difference with the number of DIMMs.
     
  11. Korican100 macrumors 6502a

    Korican100

    Joined:
    Oct 9, 2012
    #11
    but there was a noticeable difference in the geekbench's memory performance for 12gb(3x4) vs 16gb (1 stick) single/multi score.

    Would a difference that big be "felt" by the user?
     
  12. AidenShaw macrumors P6

    AidenShaw

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    #12
    Only if that user's main application is to run geekbench memory tests! ;)

    Look at the link again - most applications were virtually tied at 1 DIMM and 4 DIMMs.
     
  13. Dartanian77 macrumors newbie

    Joined:
    Jan 17, 2015
    #13
    Even if the single 16GB does not perform quite as well as 4 pieces 4GB, it certainly will trounce those 4X4 when the second 16GB is added later. For that reason I strongly vote for the one piece 16GB
     
  14. koyoot macrumors 601

    koyoot

    Joined:
    Jun 5, 2012
    #14
    3 sticks of 1866 MHz RAM will get 45 GB/s of bandwith, 16 GB, depending on the clock of it, will get only 15 GB/s at max.

    Thats why its not really good to have only one stick at time, if you can go up to 60 GB/s with 4 sticks.
     
  15. Riwam macrumors 6502a

    Riwam

    Joined:
    Jan 7, 2014
    Location:
    Basel, Switzerland
    #15
    Since a third part 16 GB module is not so extremely expensive as compared to the price of the nMP or the costs of software, I would wait for a while until I can buy more than one 16 GB stick at the same time. I preferred to keep my three 4 GB modules bought from Apple just in case I must send the nMP for repair to Apple or want to be sure that a possible problem is not due to the 16 GB modules I bought from a non Apple dealer. By selling at a such a low price those 3 modules to OWC they make actually the profit and you will not get much wealthier, so why do it?
     
  16. AidenShaw macrumors P6

    AidenShaw

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    #16
    Those are peak theoretical numbers - not how an application will perform.

    Most of the time applications read/write from/to the caches - at much higher speeds.
     
  17. koyoot macrumors 601

    koyoot

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    Jun 5, 2012
    #17
    Agreed.
     
  18. AidenShaw macrumors P6

    AidenShaw

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    Location:
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    #18
    :confused:

    You said that one DIMM wasn't a good idea, yet you agree with my comment that most apps won't see a noticeable improvement by going from one DIMM to four.

    Which is it?

    :confused:
     
  19. koyoot macrumors 601

    koyoot

    Joined:
    Jun 5, 2012
    #19
    And which part of the whole situation is confusing? :)

    If you will need bigger bandwith of Memory, and you will not have it, you will see dumps of performance.

    In big scheme of things I dont see any contradiction.
     
  20. AidenShaw, Jan 18, 2015
    Last edited: Jan 18, 2015

    AidenShaw macrumors P6

    AidenShaw

    Joined:
    Feb 8, 2003
    Location:
    The Peninsula
    #20
    The contradiction is that simple spreadsheet-based calculations of peak theoretical bandwidth have little to do with the performance of applications.

    Xeon E5-2xxx v2 processors (the older generation processors used in the Apple MP6,1) have three levels of cache, with L3 caches in the teens of mebibytes. (It's more or less X MiB of L3 cache per processor core.)

    Most real world applications run largely from cache, and see little or no "dumps of performance" due to running on a smaller number of DIMMS.

    There are many benchmarks that show this.

    To the OP - go with a single 16 GiB. You won't be able to see any performance hit, and you can add more 16 GiB DIMMs later.
     

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