we got this computer given to us we boot it an it says in the bios screen it is a Althon xp 1800 1.5GHz in the bios bios settings there is a chose of 100 fsb or 133 fsb if we put on 133 when we boot it it says it is a Althon xp 2400 2.0GHz i get the speed difference but why does it think it is a different processer