Snow Leopard 32bit vs 64bit

[Fahad]

Here I will talk about the 64bit system introduced in Mac OS X Snow Leopard 10.6

For your information: both OS X 10.4 (Tiger) and 10.5 (Leopard) also have 64-bit support for part of the system. (The PowerMac G5 introduced in 2003, with 32bit Mac OS, can access more than 4GB of RAM? Mac OS isn't limited as much with 32bit 64bit issues as windows.)


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Common Questions
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1. What is 64 bit anyway?
2. Why isn't my Mac booting a 64 bit kernel as default?
3. How do I boot a 64 bit kernel under Snow Leopard?
4. Why aren't all my applications 64 bit?
5. Is there any "IMPORTANT" deference between 64 bit kernel and 32 bit kernel?

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Answers
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1. What is 64 bit anyway?

A. Knowing about 64-Bit is not a "MUST" for most users of OS X, but for who want to know here is a Wikipedia article.

Most applications in Mac OS X Snow Leopard are Universal Binary, which mean it will have support for both 32-bit and 64-bit processors.

Till now (version 10.6.1) the default kernel for OS X 10.6 is 32 bit which is more compatible. But Snow Leopard 32 bit kernel will still be able to run 64 bit processes that allows access to more memory, handy for some hardcore users.

Of course the 64-bit kernel (K64) allows use of a very large number of RAM, 16 exabytes to be exactly, but these only needed for servers (there is no single application that require more than 4GB~8GB ram)

With Windows you need to download a different version of the app / program / driver for different version of windows os. On Mac OS, you download 1 Universal Binary which will work on all 32bit and 64bit (if available) installs for that Mac OS.


2. Why isn't my Mac booting a 64 bit kernel as default?

A. This behavior is only for consumer Mac i.e (MacMini,iMac,Macbook etc..), only servers boot a 64-bit kernel as default (because they are the only ones who really need it).

It is recommended that users boot into 32-kernel as it's more compatible with 32-bit applications and the fact that Mac OS X Snow Leopard booted in 32 bit kernel can also create
32bit and 64 bit processes. Even 32 bit Mac OS can use high amount of system RAM, and allocate more RAM than 32 bit windows. So with Snow Leopard, you have compatibility of 32 bit kernel and performance of 64 bit processes.

Windows 32 bit is very limited. 32 bit windows cannot do anything with 64bit and its RAM allocation is very restricted.

Windows NEED full 64bit because the 32bit windows is very limited. Mac OS X is different, with 32bit kernel capable of launching 64bit processes.



3. How do I boot a 64 bit kernel under Snow Leopard?

A. If you are sure you do not have 32 bit apps / drivers and you are not going to run 32 bit apps, you can boot into 64 bit kernel by holding the 6 and 4 key while you turn on your Mac.

You can edit a Plist file to boot into 64 bit by default, I will make tutorial about this soon.



4. Why aren't all my applications 64 bit?

A. This is related to developers changing their apps to 64-bit.



5. Is there any "IMPORTANT" difference between 64 bit kernel and 32 bit kernel?

A. No, for now it's better for users to stay at 32-bit kernel, 64-bit kernel was made to handle amount of RAM that only servers needs.

I hope this helps

[DoFoT9]

very informative.

there are (of course) speed increases between the 64-bit and 32-bit applications, and that can be seen in SL with the new 64-bit applications. it is basically a 2x speed increase!

all of the applications need to be 'ported' over to 64-bit before i think SL will go 64-bit (which wont be until 10.7 i daresay).

[Fahad]

very informative.

there are (of course) speed increases between the 64-bit and 32-bit applications, and that can be seen in SL with the new 64-bit applications. it is basically a 2x speed increase!

all of the applications need to be 'ported' over to 64-bit before i think SL will go 64-bit (which wont be until 10.7 i daresay).

Yes but Snow Leopard already can make 64-bit processes while running in 32-bit kernel.

[MacMan]

Yes but Snow Leopard already can make 64-bit processes while running in 32-bit kernel.

yes, but the commands are split into 32-bit operations so that the kernel can actually run the programs.