Pros and Cons of booting my iMac i5 in 64 bit mode?

Discussion in 'iMac' started by danistyping, Jan 7, 2010.

  1. danistyping macrumors regular

    Joined:
    Dec 8, 2009
    Location:
    Boston, MA
    #1
    I didn't realize that SL automically boots in 32 bit, even on the new iMacs. I have a core i5 with 8 gigs of RAM. Assuming I boot in 64 bit mode today, will my computer now utilize all 8 gigs? Was it only using 4 gigs in 32 bit mode?

    Also, will some applications not run if I boot 64 bit? Any other info is greatly appreciated.
     
  2. Hellhammer Moderator

    Hellhammer

    Staff Member

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    Dec 10, 2008
    Location:
    Finland
    #2
    OS X has been able to fully utilize over 4GBs for long time. 64-bit mode isn't recommend as some drivers are 32-bit so it might cause you troubles.
     
  3. crut macrumors regular

    Joined:
    Dec 26, 2009
    #3
    Have done some research, the 32bit kernel can run 64bit applications (and does so by default), it can address up to 32Gb of RAM. The main reason for the 32bit by default is that a lot of existing kernel extensions (drivers etc. for applications such as Parallels and VMWare) are still only 32bit - you can't mix and match 32bit and 64bit kernel/extensions.

    You can force a boot into 64bit by holding down 6 and 4 on the keyboard when the machine boots.
     
  4. crut macrumors regular

    Joined:
    Dec 26, 2009
    #4
    As a follow up to my previous post, here is a nice article explaining it in a little more depth.
     
  5. Consultant macrumors G5

    Consultant

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    Jun 27, 2007
    #5
    4gb RAM limitation is only a windows problem.
     
  6. Hellhammer Moderator

    Hellhammer

    Staff Member

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    Dec 10, 2008
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    Finland
    #6
    Snow Leopard can address up to 16TB of RAM
     
  7. crut macrumors regular

    Joined:
    Dec 26, 2009
    #7
    In 32bit mode?

    I thought that was only in 64bit mode.
     
  8. Hellhammer Moderator

    Hellhammer

    Staff Member

    Joined:
    Dec 10, 2008
    Location:
    Finland
    #8
    Officially there is no 64-bit mode. Kernel doesn't limit the amount of RAM that can be used
     

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