RTOS

Real Time Operating System
A real-time operating system (RTOS) is a special-purpose operating system used in computers that has strict time constraints for any job to be performed. While a time-sharing OS just tries to keep the processing time minimum, RTOS has to do the processing in a specific time constraint. When an external event occurs, it is communicated to the machine using a signal, which is interpreted as an interrupt by the OS. The OS then invokes a specific process, which runs uninterrupted unless a higher priority interrupt occurs. Thus, there must be a hierarchy of priority for interrupts. While executing a higher interrupt process, the other ones should be kept in a buffer.

Why Real Time Operating Systems are needed?
RTOSs are used in environments where processes must be executed within specific deadlines.
Some of the applications of RTOSs are:
•	Missile guidance systems
•	Cell phone switching
•	Fuel injection systems
•	Medical Imaging systems
•	Airline traffic control systems

Types of RTOS

Real-time operating systems can be of 3 types:
1.	Hard Real-Time Operating System
In Hard RTOS, all critical tasks must be completed within the specified time duration, i.e., within the given deadline. Not meeting the deadline would result in critical failures.
Example: Airbag deployment systems, stock trading systems
2.	Soft Real-Time Operating System
Soft RTOS accepts a few delays via the means of the Operating system. In this kind of RTOS, there may be a closing date assigned for a particular job, but a delay for a small amount of time is acceptable.
Example: Online Transaction systems.
3.	Firm Real-time Operating System
In Firm RTOS additionally want to observe the deadlines. However, lacking a closing date might not have a massive effect, however may want to purposely undesired effects.
Example: Multimedia applications
Advantages
•	Maximum utilization of devices and systems. Thus, more output from all the resources.
•	Time assigned for shifting tasks in these systems is very less.
•	Focus on running applications and less importance to applications that are in the queue.
•	Since the size of programs is small, RTOS can also be embedded systems like in transport and others.
•	These types of systems are error-free.
•	Memory allocation is best managed in these types of systems.

Disadvantages
•	Very few tasks run simultaneously, and their concentration is very less on few applications to avoid errors.
•	The algorithms are very complex and difficult for the designer to write on.
•	It needs specific device drivers and interrupts signals to respond earliest to interrupts.
•	It is not good to set thread priority as these systems are very less prone to switching tasks.
•	RTOS performs minimal task switching.