08/22/09
I’m going to break this down because this should be really simple **** yet despite this having been discussed for months now, ad nauseam, Giz can’t even get it right.
— The ONLY systems that will default to a 64-bit kernel are the Xserves.
— ALL Macs will default to the 32-bit kernel.
— Even if you have a C2D or other 64-bit CPU you may not have an option to even launch with a 64-bit kernel, regardless if you use the 6-4 keys or use Terminal to edit the boot options.
(edit: you can force 64-bit booting by holding the 6 and 4 keys while starting up, and even if you don't, those machines will still be able to run 64-bit programs without trouble. You can also type. sudo -s (enter your password) then type nvram boot-args="arch=x86_64" (hit enter) in terminal and this will boot it with a 64-bit kernel. To change it back to 32bit just leave args="" blank)
Here is the list of "capable" Macs:
Note, that If your Mac has a model number newer than what is listed then you, too, will be able to boot using the 64-bit kernel.
— When you use a 64-bit kernel you then have to use 64-bit drivers.
—— This is why the Xserve, which will likely have no oddball or legacy peripherals connected to it default to the 64-bit kernel, though you can use the 32-bit kernel if there is a driver issue. ——Macs use a lot of different drivers from 3rd-parties for peripherals so it’s the user’s best interest to default to the 32-bit kernel.
— All the 64-bit drivers Apple is releasing are "universal" in that they are both 32-bti and 64-bit. Apple has been trying to get others to do the same.
— This was the expected result for the consumer HW since the initial announcement. Nothing ha changed!
— The only caveat is why don’t certain Macs have, at least, the option to load the 64-bit kernel. I have a 13" MBP with only the Nvidia 9400M and I can’t load the 64-bit kernel. Apparently it’s only for dual GPU MB/MBPs right now, despite me having a 64-bit CPU, 64-bit chipset and 64-bit EFI. (THE LACK OF THE OPTION IS THE ONLY MYSTERY!!!)
— 64-bit apps are the default and you can choose a 32-bit version of that app if you go into Get Info and check the box for 32-bit.
— 64-bit Safari 4.0.3 on Snow Leopard gets a 440ms on SunSpider, while 32-bit Safari 4.0.3 on Leopard does it in 880ms. In comparison a couple weeks ago Chromium was saying how it’s so much faster than Safari on Leoaprd with a 660ms score.
—— 64-bit kernel or apps does not automatically mean that apps will be faster, they may even be slower for certain tasks. This depends heavily on many factors that are too complex for this site and this already long post.