linux article 

Linux and unix are esentially the same thing.  they are both using the same commands, applications are cross compatible etc..... Mach and BSD are also like linux.  therefore u can say the mac os is based on linux.  i have a mac mini here at home as one of my computers.  I have seen the linux command line and have use it.  i have been on websites which tell me mac os x is based on linux.  linux is a free version of unix.