Real time operating systems (RTOS) are used in environments where a large number of events, mostly external to the computer system, must be accepted and processed in a short time or within certain deadlines. such applications are industrial control, telephone switching equipment, flight control, and real time simulations.
The real time operating systems can be of 2 types –
- Hard Real Time operating system:
These operating systems guarantee that critical tasks be completed within a range of time.
For example, a robot is hired to weld a car body, if robot welds too early or too late, the car cannot be sold, so it is a hard real time system that require to complete car welding by robot hardly on the time.
- Soft real time operating system:
This operating systems provides some relaxation in time limit.
For example – Multimedia systems, digital audio system etc. Explicit, programmer- defined and controlled processes are encountered in real time systems. A separate process is changed with handling a single external event. The process is activated upon occurrence of the related event signaled by an interrupt.
Multitasking operation is accomplished by scheduling processes for execution independently of each other. Each process is assigned a certain level of priority that corresponds to the relative importance of the event that it services. The processor is allocated to the highest priority processes. This type of scheduling, called, priority based preemptive scheduling is used by real time systems.
The advantages of real time operating systems are as follows-
- Maximum consumption –
Maximum utilization of devices and system. Thus more output from all the resources.
- Task Shifting –
Time assigned for shifting tasks in these systems are very less. For example in older systems it takes about 10 micro seconds. In shifting one task to another and in latest systems it takes 3 micro seconds.
- Focus On Application –
Focus on running applications and less importance to applications which are in queue.
- Real Time Operating System In Embedded System –
Since size of programs are small, RTOS can also be embedded systems like in transport and others.
- Error Free –
These types of systems are error free.
- Memory Allocation –
Memory allocation is best managed in these type of systems.
The disadvantages of real time operating systems are as follows-
- Limited Tasks –
Very few task run at the same time and their concentration is very less on few applications to avoid errors.
- Use Heavy System Resources –
Sometimes the system resources are not so good and they are expensive as well.
- Complex Algorithms –
The algorithms are very complex and difficult for the designer to write on.
- Device Driver And Interrupt signals –
It needs specific device drivers and interrupt signals to response earliest to interrupts.
- Thread Priority –
It is not good to set thread priority as these systems are very less pron to switching tasks.
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