Is there a reason an older Macbook won't run Mountain Lion? I needed Mountain Lion because some of the newer software of Apple, such as Xcode, requires Mountain Lion, but besides the iMac 27 I have, sometimes I need to go on trips and need to bring a white Macbook that I bought near end of 2007.

It is indeed a very decent Core 2 Duo notebook (besides the screen dimming a little after so many years because it is not LED type), with an Intel graphics card that is capable of playing all videos and Flash games I tried, but wonder, this Macbook can't install Mountain Lion and so I need to buy either a new Macbook Air for about $1200 or a Macbook Pro for $1800 to $2200 (depending on whether it is Retina).  Is there a reason why Mountain Lion can't be installed on this notebook?  Since it is to run Xcode mainly, graphics card performance is not needed if that may be a reason -- or for other reasons?
Apparently it has to do with 32-bit graphics cards drivers, as they do not support 64-bit EFI. 

While Mountain Lion is compatible with any Mac capable of running a 64-bit kernel, the kernel does not support loading 32-bit kernel extensions. So, since the early 64-bit Macs use 32-bit drivers, Mountain Lion won't load them.

You can find out if your computer has a 32-bit or 64-bit EFI by running the command: ioreg -l -p IODeviceTree | grep firmware-abi

It will return either &lt;"EFI64"> or &lt;"EFI32">.