What are the differences between running in 64-bit or 32-bit mode on a MacBook Pro?

Peter Tuzzolino April 19, 2012
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By default my MacBook Pro seems to run in 32-bit mode, but I had read that I can change this to 64.

My question is, should I change it? And what exactly are the differences?

I do use a lot of Adobe Software’s CS5.5. I would also like to install Ubuntu on my Mac via VirtualBox and I was wondering the same for that – 64- or 32-bit?

  1. Mike
    April 19, 2012 at 7:53 pm

    I suggest not to change it. 

    Using the default boot Mac OS X is able to run both 32bit and 64bit applications. You can confirm this by opening Activity Monitor ~ within the "Kind" column it will show you which applications are running in "Intel"=32bit or "Intel 64bit" mode.

    However if you force the kernel to run in 64bit mode it will be exclusive. No 32bit kernel extension will be able to load. Chances are some of your application or maybe even hardware won't work in that mode.

    As for the guest system in VirtualBox you are only limited by it's support. Unless you are going to allocate more than 4GB of RAM to the virtual machine guest it probably doesn't make a difference whether you are using Ubuntu 32bit or 64bit

    • Petetuzz
      April 19, 2012 at 8:32 pm

      So it seems there really isn't much of a benefit to using 64-bit as of yet. What is the purpose of the upgrade or the use of it in the future?

      • Mike
        April 19, 2012 at 10:35 pm

        While Mac OS X is able to handle more than 4GB of RAM [running in 32-bit], applications are still limited by the 32-bit address space. 
        If applications are solely running on 64-bit kernel extension they can use more than 4GB of virtual memory. Also OSX will use 64-bit registers for operations resulting in increased performance.

        In day to day office or home environment usage things don't really change. However if you work with pro tools e.g. in TV productions, other large file processing, etc. you will certainly see a gain in performance and speed.

        In general Mac OS X automatically determines which mode to use for your Mac [based on the model].
        http://support.apple.com/kb/HT3770

        Feel free to boot up in 64-bit mode e.g. by pressing the keys "6" and "4" during boot. If everything works (applications, hardware, peripherals) go ahead changing it permanantly.
        http://support.apple.com/kb/HT3773