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Real-Time Operating System

In this type of system, each job has a deadline by which it must be completed; otherwise, there will be a significant loss, or even if the output is provided, it will be utterly useless. For example, in military applications, if you wish to drop a missile, the missile must be dropped with a specific degree of precision.

In this article, we will look more into the Real-Time Operating System according to the GATE Syllabus for (Computer Science Engineering) CSE. Let us read ahead to find out more about it.

Table of Contents

What is the Real-Time Operating System?

An RTOS or real-time operating system is a special-purpose OS for computers that must accomplish tasks within severe time limitations. It is primarily used in systems where the results of calculations are used to impact a process as it is running. When an event occurs outside of the computer, it is conveyed to the computer via a sensor that is used to monitor the event. The sensor generates a signal that the OS interprets as an interrupt. When the operating system receives an interrupt, it starts a specific process or a collection of processes to handle it.


Unless and until a higher priority interrupt occurs during its execution, this process is fully uninterrupted. As a result, the interruptions must be prioritised in a specific order. The highest priority interrupt should be permitted to start the process, and the lower priority interrupts must be stored in a buffer and handled later. In such an OS, interrupt management is critical.

Because standard operating systems cannot achieve such performance, real-time operating systems need special-purpose operating systems.

The following are some examples of real-time operating systems:

  • Lynx
  • MTS
  • VxWorks
  • MTS

Why is Real-Time OS Used?

All real-time operating systems are built to complete their tasks in a specific amount of time, so they must be quick enough to meet their deadline. Time restrictions in real-time systems simply refer to the time interval provided for the continuing program’s reaction. This deadline indicates that the task must be performed within the specified time frame. As a result, air traffic control systems employ them.

Correctness of results is also a critical element of real-time systems, and they must not only produce the right results, but they must also do it within the given time limit and deadline; otherwise, even if correct results are supplied on time, the OS is judged to have failed. Real-time systems are concurrent, which means they may respond to several processes at once. Within the system, there are multiple separate jobs going on, and it replies to each one in brief intervals. As a result, real-time systems are now concurrent systems.

Even if a system is under a lot of stress, such as having to respond to several processes, it must nevertheless meet all deadlines. It still replies to all queries in a timely manner, giving real-time OS stability. Within the system, there are multiple separate jobs going on, and it replies to each one in brief intervals. As a result, real-time systems are now concurrent systems.


Real-time operating systems (RTOS) are employed in real-time applications that must meet strict deadlines. The following are some of the most common applications of real-time operating systems.

  • The radar device employs real-time running architecture.
  • Missile guidance employs real-time running structures.
  • Online inventory trade employs real-time running frameworks.
  • The cell phone switching device employs real-time running mechanisms.
  • Air site visitors manipulate structures using real-time running structures.
  • Medical Imaging Systems take advantage of real-time running structures.
  • The fuel injection device employs real-time running structures.
  • The traffic control device employs real-time running structures.
  • In autopilot trip simulators, real-time running structures are used.

Types of Real-time OS


1. Hard RTOS

All key tasks in Hard RTOS must be accomplished within the defined time frame or within the supplied deadline. Failure to achieve the deadline would result in catastrophic failures, such as equipment damage or even human life loss.


Consider airbags and a handle in the driver’s seat, both given by automakers. When the driver applies the brakes at a certain point, the airbags expand to protect the driver’s head from colliding with the steering wheel. There would have been an accident if there had been even a millisecond of delay.

Consider using online stock trading software. If someone wants to sell a specific stock, the system must ensure that the command is carried out within a certain amount of time. Otherwise, if the market drops suddenly, the trader may suffer a significant loss.

2. Soft RTOS

Soft RTOS allows for a few delays through the operating system. There may be a deadline assigned to a job with this type of RTOS, but a minor delay is allowed. Cut-off dates are thus softly handled by this type of RTOS.


Both online transaction systems and livestock price quote systems employ this type of system.

3. Firm RTOS

Firm RTOS is also concerned about meeting deadlines. However, while not having a deadline may not have a significant impact, it may have unintended consequences, such as a significant reduction in the product’s quality.


This mechanism can be found in a variety of multimedia applications.

Difference between Normal OS and Real-Time OS

  • In most operating systems, such as Windows, Linux, and Unix, time is not an important component. In Real-Time operating systems, such as those used in rocket launches and ATM machines, time is critical.
  • Ordinary operating systems handle multitasking or dealing with many processes or applications at the same time. Only one task is handled at a time by a Real-Time operating system.
  • In most operating systems, context switching is available. The Real-Time operating system does not have it.
  • Any code or process in an ordinary operating system can be modified. It is not possible to change the Real-Time OS.
  • Pre-emption at the kernel level does not exist in a typical operating system. Pre-emption is implemented at the kernel level in a Real-Time operating system.

Pros of RTOS

The following are some of the advantages of a real-time operating system:

  • Real-time applications are simple to design, develop, and run on the real-time operating system.
  • Because real-time working structures are extremely small, they require significantly less memory.
  • The maximum use of devices and systems in a real-time operating system.
  • Focus on apps that are already executing rather than those that are in the queue.
  • Because the programs are tiny, RTOS can be used in embedded systems such as transportation.
  • These systems are completely error-free.
  • In these systems, memory allocation is best regulated.

Cons of RTOS

The following are some of the drawbacks of real-time operating systems:

  • Real-time operating systems are difficult to design and implement due to their complex layout principles.
  • Real-time operating systems are quite complex and can eat up a lot of CPU time.

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