Software can be thought of as the variable part of a computer and hardware
the invariable part. Software is often divided into application software
(programs that do work users are directly interested in) and system
software (which includes operating systems and any program that supports
application software). The term middleware is sometimes used to describe
programming that mediates between application and system software or
between two different kinds of application software (for example,
sending a remote work request from an application in a computer that has
one kind of operating system to an application in a computer with a
different operating system)