Determine 32bit or 64bit of your mac OS

1

Launch Terminal app (see Applications/Utilities)

2

At prompt, type the following: "uname -a" (without the quotes) (note the blank space between "uname" and "-a" strings.

3

The terminal will display two lines of text. At the end of the 2nd line, you'll find something like either

• RELEASE_I386 i386 ; the latest "i386" means that you're running 32bits kernel
• RELEASE_X86_64 x86_64 ; the latest "x86_64" means that you're running 64bits kernel

Original Link: http://www.wikihow.com/Determine-if-You're-running-the-32-Bit-or-64-Bit-Kernel-in-Mac-oSX