I found this: ----------------------------------------------- • How to check Whether your Mac has the 32-bit EFI or 64-bit EFI : When you are reading this i m sure you understand that you can boot into full 64bit mode if your Mac has 64-bit EFI. Also note that Apple disabled 64-bit kernel support for any Macbooks, even with 64-bit EFI. So if you have an older Mac Pro, iMac and you wants to check Whether your Mac has the 32-bit EFI or 64-bit EFI just enter the following command in Terminal. ioreg -l -p IODeviceTree | grep firmware-abi And you’ll get the answer either “EFI32″ or “EFI64.” • How to boot 64-bit Kernel by default at every boot : Though you have a EFI64 and 64-bit compatible Mac your install will boot into 32-bit kernel by default. Thanx to Netkas for highlighting a trick to change default boot kernel. All you have to do is edit a string file in com.apple.Boot.plist To edit boot.plist navigate to /Library/Preferences/SystemConfiguration/com.apple.Boot.plist and open the boot.plist with text editor and find the following string. <key>Kernel Flags </key> <string></string> and change it to <key>Kernel Flags</key> <string>arch=x86_64</string> That’s it, now your installation will boot in to 64-bit kernel mode every time. So no more holding down the ‘6′ and ‘4′ keys during boot. Just in case if you need to boot the 32-bit kernel just hold down the ‘3′ and ‘2′ keys during boot. ------------------------------------------ Check if you running in 32 or 64 bits mode: open Terminal and type "uname -a" (without quotes). It should return something that ends in either i386 (32-bit) or x86_64 (64 bit) ------------------------------------------ My Mac has 64-bit EFI It works like a charm accept: everytime i boot into Snow Leopard "64 bits" my Windows 7 partition (drive) don't showing up (no problem on 32 bits), how can i solve this? Anyone????? Thanks in advance.