as per as windows and mac is concerned it is noted that mac takes lass power then windows for many obvious reasones as in windows you have background processes running which get installed by default !!! but in mac you can just have apps running after log in other than services!! also in a windows machine you have to install a anti virus which takes processor power !!!! though it may be any !!! also after start up anti virus has to constantly see for data !! hence more resources but as far as default configs are concerned you cannot compare them as one is windows and other is mac !!! also in default configs mac boots up faster hence you can bet on mac having less demand for processor !! ! but both of them are gr8 operating systems other than vista which was a disaster in computer world !!!
Source:
Have many windows and mac machines !!!!!! also my gr8 experience in computers more over read as apple states mac os x as the most advnced operating system in world !!!
