Real time Operating Systems are very fast and quick respondent systems. These systems are used in an environment where a large number of events (generally external) must be accepted and processed in a short time. Real time processing requires quick transaction and characterized by supplying immediate response. For example, a measurement from a petroleum refinery indicating that temperature is getting too high and might demand for immediate attention to avoid an explosion.
In real time operating system there is a little swapping of programs between primary and secondary memory. Most of the time, processes remain in primary memory in order to provide quick response, therefore, memory management in real time system is less demanding compared to other systems.
The primary functions of the real time operating system are to:
1. Manage the processor and other system resources to meet the requirements of an application.
2. Synchronize with and respond to the system events.
3. Move the data efficiently among processes and to perform coordination among these processes.
The Real Time systems are used in the environments where a large number of events (generally external to the computer system) is required to be accepted and is to be processed in the form of quick response. Such systems have to be the multitasking. So the primary function of the real time operating system is to manage certain system resources, such as the CPU, memory, and time. Each resource must be shared among the competing processes to accomplish the overall function of the system Apart from these primary functions of the real time operating system there are certain secondary functions that are not mandatory but are included to enhance the performance:
1. To provide an efficient management of RAM.
2. To provide an exclusive access to the computer resources.
The term real time refers to the technique of updating files with the transaction data immediately just after the event that it relates with.
Few more examples of real time processing are:
1. Airlines reservation system.
2. Air traffic control system.
3. Systems that provide immediate updating.
4. Systems that provide up to the minute information on stock prices.
5. Defense application systems like as RADAR.
Real time operating systems mostly use the preemptive priority scheduling. These support more than one scheduling policy and often allow the user to set parameters associated with such policies, such as the time-slice in Round Robin scheduling where each task in the task queue is scheduled up to a maximum time, set by the time-slice parameter, in a round robin manner. Hundred of the priority levels are commonly available for scheduling. Some specific tasks can also be indicated to be non-preemptive.