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The title pretty much says it all, I need to know because I want to install new software that has these two versions, and I need to know which one to install.

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What version of the OS are you running? When was your MacBook Pro built? – Daniel Aug 31 '11 at 13:42
It's quite simple. Go to the Apple logo and select "About this Mac." If it says Core Duo, then it is 32bit. If it says Core 2 Duo, then it is 64bit (ignore the 32bit kernel issue, it will run 64bit software just fine). Physically, if your MBP has a black keyboard, it is absolutely 64bit. The original MBPs had a silver keyboard and the 32bit units were all but replaced in early 2007. So if you purchased your model even in the later course of 2007, then it is a Mac capable of running 64bit. Also, if you are running Lion, then you are 64bit (as Lion does not run on 32bit Macs). – user10355 Aug 31 '11 at 18:15

12 Answers 12

up vote 2 down vote accepted

To tell if you are running the 32-bit or 64-bit kernel (which matters for some device drivers), launch System Profiler and click on the "Software" heading in the Contents section.

The line "64-bit Kernel and Extensions" will say "Yes" if you are running the 64-bit kernel and "No" if you are running the 32-bit kernel.

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This knowledge base article from Apple should provide you with the correct answer as it depends on how old your MacBook Pro is.

Basically if you have anything newer than an 2008 MacBook you have a 64 bit processor and OS…

Here is the cheat table

Apple processors

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This does't tell the full story but it's a start. I had a Macbook with a 64bit Core 2 Duo, but 32 bit firmware/EFI resulting in a stack that was never fully 64 bit. – stuffe Aug 31 '11 at 12:46
That is true. The line is technically blurry because the kernel may only be running in 32 bit mode but everything else is 64 bit. I'm not sure exactly when but all the new Macs are now 100% 64 bit capable - although they can still run 32 bit apps. – Nate Bird Sep 1 '11 at 13:15
According to another knowledge base article, MacBook Pro from early 2008 through mid 2010 support the 64-bit kernel, but do not use it by default. – Cristian Ciupitu Apr 5 '14 at 12:00

Run this on the command line:

getconf LONG_BIT
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Another option is to use sysctl in a shell:

$ sysctl hw.cpu64bit_capable

It’ll show 1 if the CPU is capable of running 64-bit programs and 0 otherwise.

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As you may have seen from all the answers - macs are different than other Operating Systems (OS) in that the 32 bit and 64 bit dividing line is all blurry. You can have 32 bit code run on a 64 bit CPU.

A nice overview of this subject is at Apple's 64-bit Transition Guide Keep in mind, this transition was started before Tiger was released on April 29, 2005 and is still happening.

What Is 64-Bit Computing?

For the purposes of this document, 64-bit computing is defined as support for a 64-bit address space—that is, support for concurrent use of more than 4 GB of memory by a single executable program—no more, no less.

Beginning with version 10.4, Mac OS X supports command-line 64-bit executables on G5-based Macintosh computers and 64-bit-capable Intel Macintosh computers.

Beginning with version 10.5, Mac OS X supports full-featured 64-bit applications on G5-based and 64-bit-capable Intel Macintosh computers.

Beginning with Snow Leopard, Mac OS X uses a 64-bit kernel on some Intel computers.

Also - CPU that are "64-bit" still have parts that are only 32 bits wide. Similarly, CPU that are "32-bit" also have parts that are 128 bits (or more) wide. This is why most people focus on the address space for a specific program rather than whether the hardware is "64-bit" or how much of it is "64-bit"

It really doesn't matter until you get to a more specific question. Why are you asking about this? I hope this general overview helps your understanding of what people really mean when they are discussing their bits.

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Go to the Apple Menu and select "About this Mac". If you have a Core Duo processor, you have a 32-bit CPU. Otherwise (Core 2 Duo, Xeon, i3, i5, i7, anything else), you have a 64-bit CPU.

Mac OS X is fairly bitness-agnostic, so either should work. If still in doubt, use the 32-bit version.

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For completeness, there was also the 32-bt only “Core Solo” processor used in the very first Intel Mac mini (“Early 2006”). – Chris Johnsen Apr 23 '11 at 4:13

Just run Activity monitor and find the process named kernel_task . Then look at the column Kind. If it says Intel, then you are currently running 32bit mode. If it says Intel (64-bit), then as the text says, you are running 64 bit mode.

Note: You must show All processes, from te dropdown next to the search box (filter).

Then you can check @Nate Bird's answer on what processor you have and the supported modes for it.

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The kernel's mode doesn't really matter to userland; OS X will happily run 64-bit processes under a 32-bit kernel or vice versa. – Gordon Davisson Aug 31 '11 at 13:48
The original question was about if the OS is 32 or 64 bit, not the supported architectures of the processor :) – bisko Sep 1 '11 at 7:51
The kernel is not the OS, and the kernel's mode is irrelevant to what the asker actually wants to know: which version of Eclipse is appropriate? – Gordon Davisson Sep 1 '11 at 13:04
I like bisko's answer because it helped me to find a way to tell for sure what I am currently running - 32-bit or 64-bit. I have a version of VMWare that will only run in 32-bit, and since upgrading to Lion, it boots into 64-bit, so I need to reboot and hold the 3+2 keys down upon booting up to make it run in 32-bit mode. Without actually starting VMWare, it is nice to know which mode I'm currently running. It seems some of my other applications run better also in 32-bit mode. Thanks for all the different angles of answers to the main question. – user13821 Nov 18 '11 at 2:56
bisko is correct but just wanted to add, Apps > Utilities > Activity Monitor, in the activity monitor viewing cpu go to top menu, View > Columns > Kind, as well as, View > All Processes. Mine read 64bit on most processes running, not just the kernel_task. 09' MacBook, Yosemite. – user127214 May 9 '15 at 20:27

In a terminal window type uname -m. If you get x86_64 then you have 64bit OSx running.

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While this will work, there are several far simpler options that don't require a novice user to enter Terminal. – jbharper2 Dec 12 '12 at 5:15
Also this only gives you the arch of the kernel. On a Core2Duo (a 64 bit CPU) you still only run a 32bit kernel if the bootrom of that machine is not 64bit clean. You can still (and should) use a 64bit Eclipse on that machine. – MacLemon Dec 12 '12 at 14:45

The arch command with no arguments will display the machine's architecture type.

The results (from the arch(1) manpage):

i386    32-bit intel
ppc     32-bit powerpc
ppc64   64-bit powerpc
x86_64  64-bit intel
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Uh, no. I have a Core i7 MBP and have the 32-bit kernel enabled since my employer's VPN software requires it, and arch returns i386 for me. My processor is 64-bit and i have lots of 64-bit processes running, though, so this seems to only tell you what the kernel type is. – David Apr 22 '11 at 23:42
What David said - this only tells you what kernel is running. Like David, I'm using a 32-bit kernel because I need a kext that requires it, but I can run 64-bit user processes with no problem. – Sherm Pendley Apr 23 '11 at 1:05

OS X doesn't have an overall 32/64-bit mode; it simply runs each program in the "best" available mode, based on what the CPU's capable of and what the program supports. Many OS X programs come in universal binary format, meaning that they have multiple versions (some combination of PowerPC 32-bit, PowerPC 64-bit, Intel 32-bit, and Intel 64-bit) included in the same file.

Eclipse apparently doesn't come this way, so you have to decide which version to download. I'm not familiar enough with it to know if it has to run in the same mode as what you're trying to debug; if so, run your program, and look for it in Activity Monitor to see what mode it's running in. If Eclipse doesn't have to be in the same mode (or the Java code just runs inside Eclipse), then you can use either one (unless you're on a 32-bit-only CPU, i.e. Core Solo or Core Duo).

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Run in Terminal:

sysctl hw.cpu64bit_capable

If it gives 1, it means your computer has 64-bit architecture.

Or use arch command which could return either i386 (32-bit Intel) or x86_64 (64-bit Intel).

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Running arch gives "i386". In the mean time, sysctl hw.cpu64bit_capable gives 1. Then which is it? – Gajus Jun 25 at 8:39

On the command line you could run ...

printf '\n\n'
echo 'System Software Overview:'
system_profiler SPSoftwareDataType | sed -n '/64-bit/s/[[:space:]]*\(.*\)/\1/p'
ioreg -l -p IODeviceTree | sed -n '/firmware\-abi/s/.*"\([^"]*\)".*"\([^"]*\)".*/\1: \2/p'
printf '\n\n'
echo 'Java:'
#man java_home | cat
#/usr/libexec/java_home -h  
#/usr/libexec/java_home -V
#/usr/libexec/java_home -X
/usr/libexec/java_home -d 32
/usr/libexec/java_home -d 64
printf '\n\n'

# sample output:
# System Software Overview:
# 64-bit Kernel and Extensions: No 
# firmware-abi: EFI64
# Java:
# /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
# /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

As already stated by Gordon Davisson, fat binaries may include both 32-bit and 64-bit executables of a program (see also Multiple Architecture, Single Build).

file /mach_kernel /usr/lib/libSystem.dylib
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