What Is Real-Time Operating System (RTOS)?

Last Updated: 2021-11-18
Summary: Real-Time Operating System (RTOS) is one of the most important components in today’s embedded systems and takes responsibility for everything from scheduling tasks to enable advanced languages. So this article will give a full introduction to RTOS.


RTOS, short for real-time operating system, is an operating system (OS) designed to serve real-time applications that process data input without buffer delays.

Processing time requirements, including any operating system latency, are measured in tenths of a second or less. A real-time system is a time-bound system with a well-defined fixed time limit. In such a system, processing must be done within the specified constraints. Otherwise, the system will fail.

They are either time-sharing or event-driven. The time-sharing system switches tasks based on clock interrupts, while the event-driven system switches tasks based on task priority.


RTOS consists of multiple essential components.

  • Fast dispatch latency: It’s an interval between the end of the task, which can be identified by the OS, and the actual time taken by a thread.
  • Function Library: As an important element of RTOS, it acts as an interface to connect kernel and application code. This application enables users to use the library to send requests to the Kernel so that the application can achieve the desired results.
  • Memory Management: It is the most important element of RTOS. The system needs it to allocate memory to each program.
  • Symmetric Multiprocessing (SMP): It is multiple different tasks that RTOS can handle. Thus, parallel processing can be done.
  • The Scheduler: This component tells that the order in which the tasks can be performed, which is usually based on the priority.
  • User-defined data objects and classes: RTOS system use programming languages like C or C++ that need to be organized according to their operation.


  • Consume fewer resources
  • Environment is unpredictable
  • Response times are predictable
  • Take up less memory
  • The Kernel restores the status of the task and passes the CPU control of the task.
  • The Kernel saves the status of the interrupted task ad and then determines which task it should run next.


Hard Real-Time

In Hard RTOS, deadlines are strictly processed, which means that a given task must start at the specified scheduled time and must be completed within the assigned duration.

Firm Real-Time

This type of RTOS also needs to meet deadlines. Missing deadlines may not have a significant impact, but can lead to undesirable effects, such as a massive reduction in product quality.

Soft Real-Time

It accepts some latency from the Operating System. In this type of RTOS, a deadline is assigned to a particular job, but a short delay is acceptable. Therefore, the deadline is handled gently by this type of RTOS.

Terms Used In RTOS

  • Absolute deadline
  • Deadline of a job
  • The execution time of a job
  • Job
  • Processors
  • Release time of a job
  • Response time of a job
  • Task

Factors For Selecting RTOS

  • Embedded system usage: RTOS program is small in size. So RTOS is widely used in embedded systems.
  • Error-free: The RTOS system is error-free. So it will not receive errors when performing tasks.
  • Maximum Consumption: We can achieve maximum Consumption with RTOS.
  • Middleware: If there is no middleware support in RTOS, a time integration issue with the process will occur.
  • Performance: It is the most important factor to consider when RTOS.
  • Task shifting: Tasks take very little time to shift.
  • Unique features: A good RTOS should have some extra features.

Finally Words!

RTOS is an important and indispensable part of today’s embedded systems. But the system focuses on only a few tasks, which is the biggest drawback of RTOS. After going through the above contents, you may have a better understanding of RTOS.

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