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My Macbook Pro is running on Intel Core 2 Duo 2.26 GHz. OS - Leopard 10.5.8. My assumption is that all Core 2 Duo processor systems are 64 bit. But uname -m command outputs i386. Why is it so?

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2 Answers 2

Reset to default
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It's because, by default, Mac OS X boots in 32-bit, excepts some recent models.

Quoted from Apple KB Mac OS X v10.6: Macs that use the 64-bit kernel :

This Mac uses the 64-bit kernel by default in Mac OS X v10.6 : 

 - Mac Pro (Mid 2010)

These Macs use the 64-bit kernel by default in Mac OS X Server 10.6 :

 - Xserve (Early 2008) and later
 - Mac Pro (Early 2008) and later
 - Mac mini (Mid 2010)

These Macs support the 64-bit kernel, but do not use it by default : 

 - iMac (Early 2008) and later
 - MacBook Pro (Early 2008) and later

Here is a little software that can help you to boot in 64-bit if your hardware supports it.

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    Only the most recent Xserves (2009+), the new Mac Pros (2010+) and the new Mac mini start up in 64-bit by default when running Mac OS X Server and only the new Mac Pros when running Mac OS X. See support.apple.com/kb/HT3773 as well
    – Chealion
    Sep 3, 2010 at 19:20
  • And note that you can still run 64bit apps and use lots of ram just fine!
    – Mobs
    Sep 5, 2010 at 13:12
  • Also, 2011 MacBook Pros start in 64-bit mode.
    – David
    Apr 26, 2011 at 22:22
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uname is intended to be a very broad brush. It's of use to find out the continent on which you have landed soon after arrival on planet UNIX. Your kernel is 32 bit with that i386 answer.

system_profiler SPHardwareDataType and system_profiler SPSoftwareDataType are the tools for figuring detailed processor and kernel specifics at runtime.

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