Snow Leopard and 64-bit
It looks like not all users understand about 64-bit support in snow leopard.
So, here is how it works:
on all Macs, except xserve, system boots by default 32-bit kernel.
This (32-bit) kernel can run 64-bit apps just fine on core 2/core i7 based cpus.
64-bit kernel works only on macs with 64-bit efi, this is limitation set by Apple, technicaly 64-bit kernel can be launched by 32-bit efi just fine.
also Apple disabled 64-bit kernel support for macbook with 64-bit efi and intel graphics.
64-bit Kernel can run both 32 and 64 bit apps.
On hackintosh only cpus with ssse3 can run 64-bit kernel/apps, its core2/corei7 based cpus.
if kernel is 64-bit, then it can load only 64-bit kexts.
if kernel is 32-bit, then it can load only 32-bit kexts.
Userspace program cant load plugins with other architecture, for example menumeters will work only when you booted legacy, so menubar created by 32-bit application.
Quicktime uses InterProcess Communications(IPC) to load 32-bit codecs in 64-bit player.
64-bit safari uses IPC to load 32-bit flash player plugin.
To try to boot x86_64 kernel on Macintosh, edit this file:
/Library/Preferences/SystemConfiguration/com.apple.Boot.plist
find there:
<key>Kernel Flags</key>
<string></string>
and change it to
<key>Kernel Flags</key>
<string>arch=x86_64</string>
BTW - I hear another way to boot the 64bit kernel is by holding down the 6 AND 4 keys at power-up/boot. (You can verify that you've booted w/64bit kernel by checking apple system profiler Software section's main "System software overview" listing to see if the "64-bit Kernel and Extensions" item shows "Yes".)
