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Re: 64-bit Mac OS X kernel
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Re: 64-bit Mac OS X kernel


  • Subject: Re: 64-bit Mac OS X kernel
  • From: Bill Northcott <email@hidden>
  • Date: Fri, 21 Aug 2009 16:06:26 +1000

On 21/08/2009, at 2:48 AM, Mo McRoberts wrote:
The PowerMac G5 shouldn't have being advertised as 64-bit if the kernel
wasn't...
hey, even Carbon or Cocoa isn't 64bit (I don't care which API).

There are plenty of 64-bit Cocoa apps on 10.5. 64-bit libSystem-only apps can run on Tiger, as far as memory serves. The PowerMac G5 is a 64-bit machine. It doesn't stop being a 64-bit machine if you decide to only run 32-bit apps.

Similarly, a 64-bit _kernel_ is mostly irrelevant for the vast
majority of people. All it means in practice is that your kexts will
break.

As I understand it, the kernel in Darwin/OS X is not tightly linked to userland code. Only kernel extensions (kexts) have to match the architecture of the kernel. So a 32 bit Intel kernel can support 64 bit Intel code and 32 bit ppc code via Rosetta.


This has been true since 10.4 Tiger which could support 64 bit UNIX type tools as long as they only needed a limited range of libraries. 10.5 Leopard introduced 64 bit into all libraries including the GUI. (Cocoa on Leopard is 64 bit, Carbon is deprecated and was only ever intended to provide temporary (9 years) support in OS X for old OS 9 apps.)

I have no NDA information on 10.6 but I think Apple has been quite clear that it will have a 64 bit kernel and therefore require 64 bit kernel extensions, All Apple's current hardware is 64bit. The 64 bit kernel was not introduced earlier to avoid Vista style driver issues.

Bill Northcott

PS All this of course demonstrates the inherent silliness of people arguing about whether some system is 32 bit or 64 bit!

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