Real-Time Operating System (RTOS)

May 26, 2016

What Is a Real-Time Operating System (RTOS)?

The heightened reliance on technology to execute crucial tasks led to the development of high-performance and deterministic operating systems, including real-time operating systems(RTOS). An operating system is software that facilitates hardware to receive and execute user commands. Operating systems are needed for scheduling tasks, memory and file management, and for access to hardware resources.

real-time operating system (RTOS) is an operating system that works in real time, with deterministic constraints that require efficient time usage and power to process incoming data and relay the expected results without any unknown or unexpected delays. RTOS software is time dependent, meaning that it should process input and offer output within a short predetermined deterministic period. However the key to an RTOS, and the most important demand of RTOS software is that a request and response for data is guaranteed to occur. If a Windows OS has request and response calls that are fast 90% of the time, yet the remaining 10% of the time an input/output request takes too long, then the real-time application is not performing correctly. Thus an RTOS is not meant to be only fast, it is more importantly meant to be dependable

Components of a RTOS

A real-time operating system includes multiple components:

The scheduler: This is the main RTOS element that determines the order of execution of tasks or threads usually based on a priority scheme, and either in a run to completion or round robin fashion. Some RTOS may try to load balance thread across processors but most require developers to assign process affinity to cores to optimize real-time application resource usage.

Symmetric Multiprocessing (SMP): An RTOS has the ability to handle and separate multiple tasks or threads so that they can be run on multiple cores to allow for parallel processing of code (i.e. multitasking).

Function library: Is a standard interface that can contain an application program interface (API) to call routines within it, this is the interface that connects that application code and the kernel. Application code entities direct requests to the kernel via the function library to prompt the application to give the desired programmatic behavior.

Fast dispatch latency/context switch time: Dispatch latency represents the time from when the operating system identifies that a task has finishedanuntil a ready to run thread is started or when an event is triggered that causes a higher priority tasks to preempt a currently running task. The context switch is the time it takes for the scheduled to switch from one running thread to another thread, this involved saving off the context of the current task and replacing it with the context of the new thread to run.In an RTOS, the switching time should remain deterministic and minimal.

User-defined data objects and classes: An RTOS relies on programming languages with data structures that are organized based on their type of operation. The user defines object sets through a specified programming language like C++ that the RTOS will use in to control the specified application.

Memory Management: Memory management is required to allocate memory for every program to be run or object to be referenced in memory. In an RTOS this is important, since unlike General Purpose OSes like Windows it can’t afford to have memory paged in or out since it leads to non-deterministic behavior.

Types of Real-Time Operating Systems

Real-time operating systems are classified into three types:

Soft real-time systems

Meeting command deadlines in soft real-time operating systems is not compulsory for every task. However, the systems should always give the expected results. A soft RTOS requires that a response be logically correct and occur before a certain deadline or the result becomes increasingly inaccurate. Essentially the result can still hold some value even though it occurred after the required deadline.

Hard real-time systems

A hard real-time system is a time constrained and deterministic system that responds within a specified time frame. They are dictated by deadlines, latency and time constraints. For instance, if an output is expected within 10 seconds, the system should process the input and give out the output by the 10th second. Note that the output should not be released by the 9th or 11th second to prevent the system from failing.

Applications of Real-Time Operating Systems

An RTOS can be flexible but is usually designed for set purposes. Most RTOS subsystems are assigned certain tasks and leave anything and everything else not designated to it for the Windows OS itself to handle. An RTOS offers mostly operational solutions, including applications such as:

Control systems: The RTOS is used to monitor and execute control system commands. Real-time systems are used to control actuators and sensors for functions like digital controllers. Controlled systems include aircraft, brakes, and engines. Controlled systems are monitored with the help of sensors and altered by actuators. The RTOS reads the data from sensors and then performs calculations and moves the actuators so that movement in a flight can be simulated.

Image processing: Computers, mobile gadgets, and cameras must achieve their intended duty in realtime, which means that visual input is needed in real-time with the utmost precision so that industrial automation, for instance can control what is happening on conveyors or an assembly line when an item is moving down its path and there is a defect, or the item has moved its location. Real-time image processing is essential for making real-time adjustments for moving objects.

Voice over IP (VoIP): VoIP relies on Internet protocols to transmit voices in real time. As such, VoIP can be implemented on any IP network like intranets, local area networks, and the Internet. The voice is digitalized, compressed and converted to IP packets in real time before being transmitted over an IP network.

Considerations for Choosing an RTOS

Is an RTOS right for your computing needs? Consider the following factors.


Performance is a core factor that must be considered when choosing an RTOS. Real-time operating systems are different and perform differently. Key aspect for an RTOS is that its determinism guarantees that request and responses of data happen within a set period of time no matter what else is happening in the PC system. When determining the best RTOS, ask questions such as whether the system is showing any jitter within your tolerance range and thereby providing the determinism that you need. RTOS performance should be determined by a system’s dependable in executing calls within a specified period, regardless of anything else happening on the system.

Unique features

Every real-time operating system has unique features that determine how it operates to execute commands. As such, you must evaluate the features required to run your system effectively and choose an RTOS with the relevant features. A good RTOS should be scalable and feature efficient memory protection systems.

Your IT team

Most people overlook their IT team when selecting the ideal RTOS. A good RTOS should favor your IT team by reducing their labor intensity so they have more time to focus on product differentiators and learn how to setup and integrate a real-time operating system. So, decide on an RTOS that your IT team is familiar with and can work with.


Almost all real-time operating systems feature middleware components or third-party components that are integrated with the RTOS. You should evaluate the middleware to ensure that it has a seamless integration method. If your RTOS lacks middleware support, you may have to deal with time-consuming integration processes. Ensure that your middleware features components like TCP/IPand file systems.

real-time operating system should be of premium quality and easy to navigate. Developing embedded projects is hard and time-consuming; developers should not have to struggle with real-time system-related issues that can be distracting. An RTOS should be a trusted component that any developer can count on.

Good examples of real-time operating systems are the RTX (32-bit) and RTX64 (64-bit) solutions that allow you and your team to focus on adding value to your applications. This software is designed to serve as a hard real-time system that delivers output within a specified time frame to improve embedded systems’ quality.