Operating System.....
An operating system is a layer of software which takes care of technical aspects of a computer's operation. It shields the user of the machine from the low-level details of the machine's operation and provides frequently needed facilities.
Operating systems may
be classified by both how many tasks they can perform `simultaneously' and by
how many users can be using the system `simultaneously'. That is: single-user or multi-user and single-task or multi-tasking. A multi-user system must clearly be
multi-tasking. The table below shows some examples.