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I have a new 15" MBP, model MacBookPro5,3. OS is Snow Leopard, and firmware is EFI64. I can't boot into a 64 bit kernel while holding down 6 and 4 during boot.

I see a lot of conflicting info about running a 64 bit kernel (see here for example). Should I be able to run in 64 bit mode?

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migrated from Oct 12 '09 at 19:17

This question came from our site for system and network administrators.

What happens when you attempt to boot in 64bit mode? Does it just reboot? Are you getting any error messages? What is in your console log? – Benjamin Schollnick Oct 12 '09 at 20:01

I always heard that it ships with the 64bit kernel but it is not enabled by default.

To get to it, during startup, hold the 6 + 4 keys together. This should force your mac to start in the 64 bit kernel.

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You are already running in 64bit mode even if you are not using a 64bit kernel. At the moment, you don't need a 64bit kernel as most drivers are still probably going to be 32bit and you may introduce new issues with things like macfuse which current doesn't work with the 64bit kernel in snow leopard, but will work just fine with the 32bit kernel. All 64bit applications will continue to work fine and run in 64bit mode on the 32bit kernel, so at this moment there is no need to run the 64bit kernel until Apple releases the update which makes it default.

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If it's a new 15" MBP it should be able to boot in to 64 bit without issue. Also, as far as I know, the information on the page you linked is correct and up to date.

You should have free installation support from Apple. Feel free to ask them for advice.

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This site provides an application that lets you select either the 32 or 64 bit kernel. The change stays in effect until you elect to change it again.

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