Please note that the content of this book primarily consists of articles
available from Wikipedia or other free sources online. Time is a command
in the Unix operating systems. It is used to determine the duration of
execution of a particular command.The term 'user CPU time' can be a bit
misleading at first. To be clear, the total time (real CPU time) is the
combination of the amount of time the CPU spends performing some action
for a program and the amount of time the CPU spends performing system
calls for the kernel on the program's behalf. When a program loops
through an array, it is accumulating user CPU time. Conversely, when a
program executes a system call such as exec or fork, it is accumulating
system CPU time.
