What is the maximum possible ram in a Mac Pro 5,1? Different sites have different answers.

Discussion in 'Mac Pro' started by eyeangle, Jan 15, 2017.

  1. eyeangle macrumors member

    eyeangle

    Joined:
    Jan 2, 2014
    Location:
    Melbourne, Australia
    #1
    Specifically the 6-Core model because that's what I own.

    According to this table from OWC:
    https://eshop.macsales.com/shop/mem...1.204008400.1181529146.1468163367#1333-memory
    48GB (3x16GB) is the maximum ram I can have.

    But I saw a video on YouTube from someone who has the same Mac Pro 5,1 as I do and they have 64GB (4x16GB) so I emailed OWC about this and what they had to say,

    "64GB would only be possible using 8x8GB or 4x16GB. Your model has 4 slots and could physically fit 4x16GB but that is not stable, the ram processor cannot handle that amount. Per extensive OWC testing only the 3x16GB is stable."

    I also emailed the person on YouTube and they said 64GB worked fine so I'm curious to know how much ram you have and what is your maximum? Have you found that the ram processor can handle over 48GB if you have so?
     
  2. owbp macrumors 6502a

    owbp

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    Belgrade, Serbia
    #2
  3. nbritton macrumors regular

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    May 22, 2008
    #3
    If you can find non load-reduced 32GB PC3L-12800R modules, the Mac Pro 5,1 can theoretically support up to 256GB. I have yet to see anyone who has done this. I was thinking about it, but the RAM costs like $2k. I recall Sk-Hynix makes non-load-reduced 32GB modules. Right now I have 128GB in mine, which is a dual socket Xeon X5690.
     
  4. mastermamo macrumors member

    mastermamo

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    Cape Town South Africa
    #4
    In theory the max usable memory is 96gigs on OSX and 128gigs if u r using windows on mac. This applies to most dual CPU Macs from 2010 upward
     
  5. nbritton, Jan 16, 2017
    Last edited: Jan 16, 2017

    nbritton macrumors regular

    Joined:
    May 22, 2008
    #5
    They upped it from 96GB, the current limit is unknown though. I've asked several times what the upper limit is in Mac OS and everyone replies back quoting the limit for virtual memory. However, virtual memory is not the same as how much physical memory Mac OS can address. I can confirm with absolute certainty that the latest versions of Mac OS can address 128GB, because I have 128GB (8 x 16GB) in my Mac Pro 5,1. Due to memory leaks in Safari and Flash I have on one occasion actually run out of memory (perf mon showed all 128GB of ram in use, plus it was using several gigabytes of swap space), so I can further confirm that Mac OS can utilize all 128GB of ram.
     
  6. mastermamo macrumors member

    mastermamo

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    #6
    So at 128gig in do u notice any significant increase in speed/performance? If so, what software are these seen in?
     
  7. nbritton macrumors regular

    Joined:
    May 22, 2008
    #7
    Nope, from a performance stand point it behaves no differently then if I had 64GB. In fact, when memory usage gets really high the systems starts to slow down a lot. I think this slow down could be due to memory compression being turned on, if I disabled memory compression I might see a large speed up, but I've never tried it yet. I'll have to try it, I think this disables memory compression:
    sudo nvram boot-args="vm_compressor=1"
     
  8. mastermamo macrumors member

    mastermamo

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    #8
    If performance is the same why go the 128gig route?
    Memory compression is turned on by default if I remember correctly. Do u know what the purpose of this is?
     
  9. nbritton macrumors regular

    Joined:
    May 22, 2008
    #9
    Because I'm a power user, I usually have multiple virtual machines running, 30+ windows open, and 100 browser tabs open. Typically I idle at around 50GB of memory used. Also I happened to already have the memory, so it cost me nothing extra.

    Memory compression is just what it sounds like. It compress the memory that applications use so that they take up less physical memory, this lets you run more applications on less memory. However, it comes with a performance penalty. If I disabled memory compression I would expect to see an increase in performance.
     
  10. mastermamo macrumors member

    mastermamo

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    #10
    Can u post the terminal commands to enable and disable compression?
    Is there any danger inherent in disabling compression?

    Also what software do u use to check the amount of RAM in use at any given time?
     
  11. nbritton macrumors regular

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    May 22, 2008
    #11
  12. mastermamo macrumors member

    mastermamo

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    Jan 14, 2017
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    Cape Town South Africa
    #12
    Thanks will have a look. Interested to see what it's all about. Doubt I will use it as all my Mac Pros have 64gig installed
     

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