Can someone explain the main difference between Linux and Unix?
Unix was written at Bell Labs AT & T back in the 70s.
Linux is the Unix port for the PC, written by Linus Torvalds and released in 1991 with open source.
Note this: http://www.unixguide.net/linux/lnag/lnag1.5.shtml Linux is basically a unix-like kernel, where Unix itself is a standalone kernel.
Unix is a privileged kernel for a more select audience (i.e. servers). This is basically a decency code.
Linux is for general-purpose audiences (i.e. desktops). It is open source. Linux was based on Unix.