Got 16 GBs RAM and Windows don't ...

The answer to this is simple. Any 32bit operating system will not see or use more than 4gb of ram. Usually that is the case anyways. In my experience, especially with XP home edition, it might not even use that much it would see anywhere between 2 and 3.5. I suggest at least installing XP pro, but you would be doing much more good by having an x64 version of windows if you want it to function properly on a mac that new. The hardware in the computer is aimed toward newer systems like vista and 7. Yes XP will run, but the hardware is beyond XP. The best chance you'll get is either installing XP Pro x64, or any version of windows server 2003. That is of course if you must be using XP.
as for it seeming faster, of course it does. Windows XP has a minimum requirement of a 266mhz cpu with 64mb of ram, or something like that. essentially this computer is over kill for it, so it seems faster.
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx

If you want to use more than 4gb in windows, you have to install a 64bit OS, or a windows version that supports PAE.

A portion of that address space is tied up with other thing. I don't remember them at the moment, but it is normal.

Don't bother with x64 version of XP or Vista, none of those are supported by Bootcamp anymore. Your best option is IMO 64bit version of Windows 7.

Sincci said:

Don't bother with x64 version of XP or Vista, none of those are supported by Bootcamp anymore. Your best option is IMO 64bit version of Windows 7.

Click to expand...

Or Windows 8.