When you enter 'ls' command to look at the contents of your current working
directory, UNIX does a series of things to create an environment for ls and the
run it: The shell has UNIX perform a fork. This creates a new process that the shell
will use to run the ls program. The shell has UNIX perform an exec of the ls program.
This replaces the shell program and data with the program and data for ls and then
starts running that new program. The ls program is loaded into the new process context,
replacing the text and data of the shell. The ls program performs its task, listing
the contents of the current directory.