Real-Time Systems in Operating System:
A real time system is a system that ensures the exact time requirements for a job. If a real-time system does not complete a task in a certain time, it may cause a break down of the entire system it is running.
Some applications require to be serviced within a time period:
Industrial control systems
Automobiles (brakes)
Airplane guidance
Medical devices
Types of Real-Time Systems:
There are two types of real time systems:
1. Hard Real Time Systems:
A hard real time system guarantees that a job will complete within a specified time period. This system must ensure that all delays on processing, input and output are bounded. The system cannot wait indefinitely so the hard time systems are usually very limited. There is generally no secondary storage such as disk drives as a disk request can take a variable time to process.
Some examples of a hard real time system are the software that run the autopilot in an jumbo jet or the imaging software on a missile.
2. Soft Real Time Systems:
A soft real time system is a much less restrictive version of a hard real time system. A soft real time system does not guarantee that a job will complete within a specified time period. However, it tries its best to finish the job as soon as possible. If a critical real time job enters the system, the operating system may assign the highest priority to that task and execute it continuously until it completes.
The lack of a guarantee makes a soft real time system more limited in its application for industrial activities. Soft real time systems are used in multimedia, virtual reality etc. The operating systems that provide soft real-time support are Windows NT/2000, Linux, Solaris.
