How do I force my Mac to always boot Snow Leopard in 64-bit mode?

1. Launch TextEdit
2. Open the file named /Library/Preferences/SystemConfiguration/com.apple.Boot.plist
3. add arch=x86_64 to the Kernel Flags string:

…
<key>Kernel</key>
<string>mach_kernel</string>
<key>Kernel Flags</key>
<string>arch=x86_64</string>
...

—-

Then to switch back to the 32-bit kernel, hold down the “3” and “2” keys during boot, or replace “x86_64” with “i386” in the .plist file.

(source)

I definitely recommend reading the Ars review (linked as source above). John Siracusa explains, in detail, why it is that you probably don’t really need to default boot to 64-bit mode.

Furthermore, I would guess that if you didn’t already know how to edit a .plist file for yourself, chances are you won’t be able to support the special situations that could arise from booting into 64-bit mode by default.

So take caution.

Are there any disadvantages to doing this?

@robmandu Thanks a lot! I read Wired.com myself; maybe I should check out Ars Technica more often.

I will read the article and consider the costs and benefits of such a change before I edit anything.

@brettvdb Check out the link Rob so graciously posted for us. I think it will tell you the disadvantages pretty clearly.

Oh sorry I didn’t even see that link there the first time through!

Hmm, so it seems the main reason why you wouldn’t want to boot into 64-bit mode is because some of your devices may not work (i.e. printers, external hard drives, etc.)

With this said, I will just try it and see what works; then I will see if its for me or not. All I really care about is whether or not my G-Drive works. I’ll let you guys know how it turns out!

@brettvdb No problem, my friend, just read more closely.

:/ Strangely, my Mac is telling me I don’t have permission to edit this file. I have an administrative rights and the ability to read and write to files.

Scratch that, I just had to change some permissions on the file and on the folder. It worked this time! :)

Also, see this.

What benefit do you think you’ll get by running in 64-bit mode all the time?

@cwilbur That article seems to provide the same info that the Apple Insider, 9-to-5 Mac, and Ars Technica articles provide.

I think Ars Technica makes a good case for why you would want to run in 64 bit mode all the time, and why you would not. According to them, the main problem you will have is with hardware compatibility. And regardless, I still want to just try it and see what it’s like; it seemingly won’t break anything, so why not? If I find that it impedes my regular computing, then I will switch back.