Should I use the 64-bit mode with my Mac?

By On August 23, 2010 · 12 Comments

Question: When Apple released Mac OS X 10.6 Snow Leopard, they talked about a 64-bit kernel and being able to use applications under that mode. I want speed. Should I use 64-bit?

Answer: There sure are good reasons to use the 64-bit mode but it is not everyone who can do it.

The first reason would be your use of ramdom-access memory (RAM). If you have more than 4 GB installed in your Mac, this allows your software to access it. The second is speed. 64-bit operations require less steps, therefore less time to execute.

However, things are never quite simple. As we write this, there are two big issues that prevent full use of 64-bit.

The first is simply the hardware. Not every Mac can boot into 64-bit mode. Apple provides a list of computers that support 64-bit with Snow Leopard.

32-bit

No 64-bit here. Grrrr.

The second is that not every application is fully compatible. For instance, one of the applications that can benefit from this the most is Photoshop. Only version CS5 is 64-bit compatible.

How to switch

If your Mac is compatible but does not start up in 64-bit by default, here are two methods to do it.

The first, as a temporary measure, is to hold down the 6 and 4 keys at startup.

The second is one that sticks permanently. Open the Terminal application which is located in the Applications > Utilities folder.

Then, type this: sudo systemsetup -setkernelbootarchitecture x86_64

You can revert to 32-bit with the following command: sudo systemsetup -setkernelbootarchitecture i386

 
  • Nate

    Snow Leopard runs 64-bit-capable applications in 64-bit mode even when booting into the 32-bit kernel…

  • Bradley Dichter

    If you have more than 32 GB of RAM in your Mac Pro you must boot in 64-bit mode in order to use all of it. Also when you are in 64-bit kernel mode, you must have 64-bit drivers for PCIe cards and printers, scanners, etc. 64-bit kernel should not be confused with the more common 32-bit kernel and 64-bit apps like Photoshop CS5 or Lightroom 3

  • Peter DeArmond

    There are some PCIe devices, such as the Sonnet RAID card, that will work in 32-bit mode while you are booted up in 64-bit mode on your new Mac. However, the Lycos driver only works if you’re booted up in 32-bit mode. If you’re doing video and you want to use the new version of After Effects, you will want a lot of RAM and you’ll need to boot up in 64-bit mode so that AE can eat up as much as it can.

    Also, on the new Macs, there’s an easier way to boot up in 32 or 64-bit mode: In your Applications folder, click once on System Preferences and Get Info. If you check the box that says “Open in 32-bit mode” your Mac will always boot up that way until you uncheck the box. Otherwise, the new Mac Pros (the ones that went on sale this month) will boot up in 64-bit mode by default.

  • Bradley Dichter

    I’m pretty sure the 32-bit mode of the System Preference panel will not effect the way the Mac boots up. If you are afraid of Terminal, check out this GUI solution:
    http://www.ahatfullofsky.comuv.com/English/Programs/SMS/SMS.html

  • Branson

    Checked on the Apple list, iMac (mid 2010) not in the list, does not support 64-bit mode??

  • Bradley Dichter

    My Highpoint RocketRAID 3522 PCIe works fine booted in 64-bit mode.

  • Bradley Dichter

    “These Macs support the 64-bit kernel, but do not use it by default.
    iMac (Early 2008) and later”

    Branson, did you not read the “and later” part?

  • Peter DeArmond

    Re: “I’m pretty sure the 32-bit mode of the System Preference panel will not effect the way the Mac boots up. If you are afraid of Terminal, check out this GUI solution…”

    Depending on the experience and/or confidence of the user I’m advising, I tend to steer them away from the Terminal. I can’t speak for the older models, but as I said, on the new Macs, the 32-bit mode of the System Preference Get Info window DOES affect the way the Mac boots up. If the 32-bit box is checked, it WILL boot in 32-bit mode. If the box is unchecked, it WILL boot up in 64-bit mode, the default. Again, this is on the new Macs shipping this month. I can’t speak for earlier models.

    Also, see item #12 on this page:

    http://discussions.apple.com/thread.jspa?threadID=2176255&tstart=0

  • MrMotionBlur

    @Peter DeArmond: The run in 32 mode option is only for universal applications. As you can see, Safari also has this option in its info window. Some plugins or prefpanes don’t run in 64bit so you can set the default runmode to 32bit. If you run system prefs in 64bit and you click a pref pane that is 32 but only, system preferences restarts in 32 bit mode.

  • Carl

    Setting the 32/64 bit flag on System Preferences does NOT make the computer run in that mode. It’s only there to allow toggling back to running the prefs app to 32 bit when running in 64 bit mode to support old third party pref panes. It even says so in the Apple article linked.

    The way to do it properly is listed above or use a free utility. This one is the best ive found:
    http://www.versiontracker.com/dyn/moreinfo/macosx/10967003

  • Bradley Dichter

    I have a 2009 Mac Pro, and my System Preference panel’s Get Info box does not have the open in 32-bit mode and my Mac is not booted in 64-bit kernel. That trick must be for very new models.

  • Peter DeArmond

    Yes, as I said, I can only verify this on the new Macs Pros that started shipping this month. I have one, and when I set System Prefs Get Info box to run in 32-bit, the OS does in fact boot up that way (I can verify this in System Profiler). But otherwise, this computer always will boot up in 64-bit mode.