Realtime Systems.

Introduction.

Real-Time systems are computer systems in which succesful task performance depends on two factors:
- succesful result of computation,
- exact deadline time in which task was performed.

When a task execution time exceeds it's time deadline, we can say that system failed.


Hard, Firm & Soft Real-time Systems.

In the 'Hard Real-time Systems' missing a deadline is a total system failure. Hard realtime systems are created when missing a deadline can result in hardware damage or costs lives or health.

In 'Firm Real-time Systems' infrequent deadline misses are tolerable, but may degrade the system's quality of service. The usefulness of a result is zero after its deadline, but no damage or personnel loss occurs.

In 'Soft Real-time Systems' the usefulness of a result degrades after its deadline, thereby degrading the system's quality of service.


Requirements.

For a computer system to meet criteria of the 'Hard Real-time System', requirements are:
- well understood & fast enough hardware,
- real-time operating system (for example: RTLinux),
- every software piece must adhere to the 'hard real-time requirements'; software must generate results in the deadline time.