Multiprogramming leads to the concept of a process.
Metaphorically,a process is a program's breathing air
and living space-that is,a running program plus any
state needed to continue running it.Time- sharing is
a variation of multi-programming that shares the CPU
and memory with several interactive users at the same
time, giving the illusion that all users have their own
computers. Thus at any instance it should be possible
to switch from one process to another. This exchange
is called a process switch or context switch.
Protection and Examples of Virtual Memory.
Computer Architecture: A Quantitative Approach, Third Edition