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How do I determine if my OS X 10.9.4 is a 32 bit or 64 bit operating system?
I've looked at "About This Mac" but don't understand what the processor information (i.e. 3.5 GHz Intel Core i7) translates into as refers to "bits.

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up vote 11 down vote accepted

I do not believe that Mavericks shipped with a 32-bit version. You are probably running 64-bit OS X.

All of the Core i3, i5, and i7 Mac computers have 64-bit processors.

Apple Support document

To determine if you are running a 32-bit or 64-bit version of OS X, open a Terminal and type:

uname -a

On a 64-bit OS, the output will end with RELEASE_X86_64 x86_64. On a 32-bit OS, the output will end with RELEASE_I386 i386.

OSXDaily article

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Thank you for early (and helpful) response. Could you be so kind as to advise how to "open a terminal"? – user86803 Aug 4 '14 at 15:40
Yes. Open Spotlight (CMD+SPACE) and type "Terminal" and click the little black box icon that appears. It is also known as a "command prompt." Or just open /Applications/Utilities and double-click Terminal. – aglasser Aug 4 '14 at 15:44
Awesome...thanks again for the rapid and useful response. – user86803 Aug 4 '14 at 15:51
Glad to help :) – aglasser Aug 4 '14 at 15:51

Easy - it's 64-bit.

Mavericks is 64-bit only :)

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OS X doesn't really have a single overall mode -- it can easily run different components (different processes, the kernel, etc) in different modes. It also has a multi-architecture binary format, so a single program can include both 32- and 64-bit code, and the OS will simply run it in whatever seems to be the most appropriate mode at the moment.

Over the history of OS X, it's gradually morphed from 32-bit only (through 10.2 I think), to fully 32+64-bit capable (10.6), to mostly-64-bit-only (10.8-10.9). Starting in 10.8, Apple removed the 32-bit versions of the kernel and most built-in apps, meaning that it'll only run on 64-bit CPUs. But it's still fully capable of running old 32-bit programs, and there are even a number of system programs that can run in either mode (again, to provide compatibility with old 32-bit software). The most visible example of this is the System Preferences, which normally runs in 64-bit mode, but can quit & relaunch itself in 32-bit mode to run old 32-bit-only preference panes (if you can still find one).

Note that there've never been separate 32- and 64-but versions of OS X. 10.6, for example, would install exactly the same on a 32- or 64-bit computer, and then decide at runtime which mode each program should run in.

Summary: it's not an entirely a meaningful question, but to the extent that it's meaningful Mavericks is a 64-bit OS.

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