OSX Mountain Lion: Still a 96GB RAM Limit?

Discussion in 'Mac Pro' started by D*I*S_Frontman, Jun 21, 2012.

  1. D*I*S_Frontman macrumors 6502

    May 20, 2002
    Lombard, IL
    Hey MR,

    I've noticed that the current DP Mac Pros can be physically upgraded to 128 GB RAM but, due to an OS limitation can only address 96GB. The same upgraded Mac CAN address all 128GB, but only when booting Windows.

    Has there been any word as to whether or not that limitation has been lifted when using 10.8 Mountain Lion? Have the techs at OWC loaded a current Mac with 128GB RAM booting ML and tested this?

    Because I know the "why would you need that much RAM" question will inevitably follow, just pretend I have a good reason. Like running a massive orchestral sample library, for example. Or DNA sequencing.

    128 GB a go in ML?
  2. Umbongo macrumors 601


    Sep 14, 2006
    The guy who got his Dual E5 hackintosh going got 128GB working. Just don't think there has been enough investigation to see what works.

    You could email OWC and ask. They may have been using quad-ranked 16GB DIMMs which could have caused issue, maybe others have had success now dual-ranked ones are available.
  3. thekev macrumors 604


    Aug 5, 2010
    No one has any imagination when it comes to things like this. Usually when someone asks about ram limits like this, I want to know what they're doing as it's most likely something interesting:D.
  4. d-m-a-x macrumors 6502

    Aug 13, 2011
    Only 96 GB of ram? Not 128GB? What amateurs...
  5. D*I*S_Frontman thread starter macrumors 6502

    May 20, 2002
    Lombard, IL
    Anyone else have an answer to the original question?
  6. The-Pro macrumors 65816

    Dec 2, 2010
    No clue but I still dont understand why there is 96GB of software limitation when apple said SL can support something around an exabyte of RAM. Dont get it!
  7. Spacedust macrumors 6502a

    May 24, 2009
    Windows Vista Business/Ultimate and Windows 7 Proffessional/Ultimate 64-bit versions can both drive 128 GB RAM easily. Windows 7 max out at 192 GB ;)
  8. TableSyrup macrumors 6502

    May 29, 2012
    I'll be happy to hear confirmation as well - as I can benefit huge from this.


    Pro Tools 10HD Disk Cache - Loads all session audio into RAM.

    I had the experience of testing a huge session loaded completely into ram, and it was like driving a rocket ship on a go kart course. AWESOME

    The more RAM the merrier
  9. deconstruct60 macrumors 604

    Mar 10, 2009
    Marketing hype --> 64 bit pointers/adressing means exabyte.

    Reality --> virtual address spaces are tracked with data structures in the kernel ( page tables to keep the mappings between virtual and real addresses , static mappings for some datastructures so not swapped out, etc.)

    Larger memory means the kernel is going to soak up more memory. Given that Mac RAM minimums are now 4GB that is easier to do now than when there were still folks running 32-bit kernels and had about 2GB of RAM total.

    The 96GB limit was a defacto "as much RAM as you could afford" limit. For most, they were kept below of that limit because couldn't afford it (and/or it made no significant performance impact). Even now it is likely less that 2% of Mac users this is an issue for.

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