BATCH

The earliest type, allowed only one program to run at a time. The program was entered into the computer, then run till completed. The data used by the program could not be modified whilst the program was running. Any errors in the program or data mean starting all over again.

INTER-ACTIVE

These allow the modification and entry of data whilst the program is running. Typical systems are airline reservations and languages such as BASIC.

TIME SHARING (MULTI-USER)

These share the computer system amongst more than one user, and employ pre-emptive scheduling techniques.

MULTI-TASKING

More than one process may be executed at once. The processor is switched rapidly between the processes. A user may run more than one process at a time.

REAL-TIME

Primarily used in process control, telecommunications, etc. The OS monitors various inputs which affect the execution of processes, changing the computers model of the environment, thus affecting the outputs, within a guaranteed time period (usually < 1 second).

MULTI-PROCESSOR

A computer that has more than one processor dedicated to running processes.

EMBEDDED

An embedded operating system means the operating system is self-contained in the device and resident in ROM. Typical systems that use embedded operating systems are household appliances, car management systems, traffic control systems and energy management systems.