Physically-Based Rendering

Just received my copy of Mac OS X 10.6 Snow Leopard!

One of the main new features of this version is its 64-bit kernel. However, there are a couple of catches: First, even if you have a shiny Intel Core 2 Duo Mac you must have a 64-bit EFI in order to boot the 64-bit kernel.

ioreg -l -p IODeviceTree | grep firmware-abi

If you get EFI64 you’re in luck, otherwise tough… I got lucky: I do have a 64-bit EFI. Nice.

Second, even then all Macs (except Xserve) boot the 32-bit kernel by default. To use the 64-bit kernel you can either press ‘6′ and ‘4′ everytime you boot your Mac, or you can edit com.apple.Boot.plist as follows:

1. Open /Library/Preferences/SystemConfiguration/com.apple.Boot.plist

2. Find the string:

<key>Kernel Flags</key><string></string>

3. Change it to:

<key>Kernel Flags</key><string>arch=x86_64</string>

That’s it, you’re set. (if you ever need to boot in 32-bit mode, just press ‘3′ and ‘2′ during boot).

_

Update (31st August):

After having made the modification above, I wanted to insure that the kernel used was indeed the 64-bit one. To do that:

uname -a

Which for me unfortunately gives:

Darwin Kernel Version 10.0.0: Fri Jul 31 22:47:34 PDT 2009; root:xnu-1456.1.25~1/RELEASE_I386 i386

Argh…

So beware: a 64-bit EFI is not a guarantee that you’ll be able to use the 64-bit kernel. Especially, apparently iMac 7,1 (my case) cannot use the 64-bit kernel in any case.

Mac OS 10.6 will be released on Friday (28th August).

It looks like it will be a nice toy for developers of resource-hungry applications:

1. full 64 bit support,
2. OpenCL,
3. Grand Central Dispath (see Apple’s technology brief on GCD) for efficient multithreaded design.

Needless to say that I’ve pre-ordered it