Understanding Real-Time Operating System, With Examples

real-time operating system

Understanding Real-Time Operating System, With Examples

Key Points

  • RTOSs are software systems that respond to stimuli in real-time and measure processing times down to tenths of a second.
  • There are three types of RTOSs: hard, soft, and firm, each with different applications and priorities.
  • RTOSs have advantages such as optimized memory allocation, error-free performance, and efficient resource usage.
  • Real-world applications of RTOSs include air traffic control, anti-lock brake systems, and self-driving cars.
  • Essential language for discussing RTOSs includes terms such as task, job, release of job, execution time of job, and deadline of job.

With the amount of data being processed on a second-by-second basis and the ever-growing network of data processing devices, we are seeing a shift and demand for more powerful real-time operating systems. Real-time operating systems currently occupy a very unique space in the technology world. But what exactly are they, and how are they being integrated into our daily lives? Let’s take a look at the ins and outs of real-time operating systems.

Define: Real-Time Operating System

A real-time operating system (RTOS) is any information processing software system that performs functions in real-time, both on the soft and hardware sides, and responds to stimuli in real-time. They see the most use in situations where the computer must react to and process external inputs swiftly and accurately.

RTOSs measure their processing times down to the tenths of a second, but some systems may measure in even smaller increments. These systems are time-bound, and responses to inputs must occur within a certain timeframe.

Processes scheduled in an RTOS run indefinitely, uninterrupted. They are given a priority rating and unless a task of higher priority is scheduled, the processes cannot be interrupted without shutting the whole system.

Types of Real-Time Operating Systems

There are three types of RTOSs. Each one has different applications and will be seen in different industries. 

Hard Real-Time Operating System

Hard RTOSs ensure that critical tasks will be completed on time. These systems strictly handle data, inputs, and processing on both hard and software sides, allowing the system to achieve its deadlines flawlessly. In cases where a hard RTOS is used, the system not meeting its deadline would cause critical failures in its current and future tasks. Thus, hard RTOSs prioritize meeting their deadlines above all else. If a deadline is missed, most hard RTOSs will shut down to prevent damage to any products or systems they influence.

Soft Real-Time Operating System

Soft RTOSs don’t handle deadlines as strictly as hard RTOSs. With a soft RTOS, delays won’t necessarily shut down the system since they aren’t prioritized over completing the task. So while the system may have an overall deadline it wants to meet, it won’t grind to a halt when there’s a small delay. This can allow for better multitasking and can be ideal for systems that don’t have many time-sensitive critical processes.

Firm Real-Time Operating Systems

Firm RTOSs are an in-between for soft and hard RTOSs. These systems observe deadlines but not as strictly as hard RTOSs. In situations where you might use a firm RTOS, the system missing a deadline won’t completely shut it down. However, these small errors might cause a degradation in the quality of the finished product. When used in production lines, products that suffered a missed deadline may be discounted or thrown away due to the quality change.

real-time operating system
One of the applications of a Real-Time Operating System is air traffic control.

Advantages of Using a Real-Time Operating System

Real-time operating systems have many advantages beyond simply doing tasks on time. Thus, they’re used in many fields where companies have the capital available to build an RTOS for their specific needs. Let’s look at why a company might choose to build an RTOS to handle their daily tasks.

Memory Allocation

Memory allocation is far more optimized in an RTOS than it is in general-purpose operating systems (GPOS). Thus, when a company needs several memory-intensive processes running, it might choose to build an RTOS to allocate memory during processes better.

Embedded Real-Time Operating Systems

RTOS programs tend to be extremely small and lightweight. Thus the hardware needed to run them is not as extensive and physically large as it would be if the system used a GPOS. Since the systems are physically and software smaller, they can be embedded in other systems that need to be used on the go, such as a transport system or a media player.

Error Free

RTOSs do not produce errors. Unlike GPOSs, RTOSs are built to specifically handle the necessary tasks without producing errors. With a custom-built system, you can test, restest, and ensure that the system performs the scheduled tasks flawlessly. You can’t do that with a GPOS.

Task Shifting

RTOSs are also much better at shifting tasks than GPOS. GPOSs need around 10 microseconds to shift tasks, while RTOS systems typically need just 3 microseconds. This can be essential in situations such as product lines where the RTOS must shift tasks regularly and often to maintain the workflow.

Maximum Consumption

RTOSs are more efficient at using resources than GPOSs. Thus, when a company wants to use all of its available resources at all times, it will tend towards RTOSs as they use all available resources instead of allocating resources to be saved.

Application Focus

RTOSs also focus more strongly on currently running applications while allocating fewer resources to applications in the queue. This allocation allows for more resources to be allocated to running each successive application correctly.

Disadvantages of a Real-Time Operating System

RTOSs also have a few major disadvantages. We’ll cover reasons that RTOSs haven’t made the break from the industries where they’re necessary.

Heavy System Resources

RTOSs have high system requirements and use a lot of resources. These factors can make them extremely expensive to implement.

Limited Tasks

RTOSs don’t run many processes concurrently. Focus is put on running single applications while putting other applications in the queue to reduce system resources and prevent the RTOS from generating an error caused by running concurrent processes.

Device Drivers and Interrupt Signals

RTOSs must use specially formulated drivers and interrupt signals to respond to application interrupts as quickly as possible. Largely, an RTOS will be implemented, particularly when a company implements a hard RTOS, because the RTOS needs to be able to interrupt the processes immediately should a delay occur. So, these drivers and signals are extremely important to implementing the RTOS and must be tailored to the specific system.

Complex Algorithms

RTOSs don’t use many common algorithms. The algorithms used in an RTOS are more complex and unique than those for a GPOS. This factor makes them harder to program for, and finding software developers qualified, able, and willing to write programs for an RTOS is more difficult than a GPOS.

Thread Priority

RTOSs don’t mesh well with thread priority since they rarely run many concurrent tasks and don’t switch tasks often.

Real-World Applications of Real-Time Operating Systems

  • Airline reservations systems
  • Air traffic controllers
  • Any system that provides immediate updates to users
  • Defense applications such as RADAR
  • Multimedia systems that connect to a network
  • Anti-lock brake systems
  • Internet telephony
  • Command Control Systems
  • Pacemakers
  • Missile guidance
  • Inventory trading
  • Precision robotics
  • Medical imaging
  • Fuel injection
  • Autopilot systems (including self-driving cars)
  • Stock trading
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The Tesla is equipped with an autopilot system using a real-time operating system.

Essential Language for Discussing Real-Time Operating Systems

Like any technological system, specific language encapsulates important information about the system. Knowing these terms is essential for talking about RTOSs with people who also understand them and allow you a smoother conversation. 


Regarding RTOSs, a “task” is a set of jobs that provide system functionality to the RTOS.


A “job” is a small piece of work that the RTOS can assign to a processor, which may or may not require additional resources.

Release of Job

This is the point of time at which a job becomes ready to be executed.

Execution Time of Job

This is how long the system takes to execute and complete any particular job.

Deadline of Job

This is the expected end time of an execution of a job.

Maximum/Relative Deadline

This is the maximum amount of time a job can take before the system interrupts the process.

Response Time of Job

This is the full amount of time the computer anticipates a job taking from the start of release until the finish.

Absolute Deadline

This is the relative deadline, the expression of the maximum amount of time a job should take.


Also known as active resources, these resources are extremely important for the execution of jobs.

Final Thoughts

RTOSs are extremely important for some industries. These little computer systems are the backbone of many industries we rely on daily. RTOSs probably won’t become popular in smaller industries or personal use for the reasons we outlined above, but it’s still pretty dang cool that we have this kind of technology at our disposal.

Frequently Asked Questions

What is a real-time operating system?

A real-time operating system is a computer system that reacts to inputs and delays in real-time.

What is an operating system that doesn’t operate in real-time called?

General-purpose operating systems are the other kind of operating systems on the market.

What are some of the most common uses of real-time operating systems?

Any system which provides real-time updates to users, air traffic controllers, and self-driving cars are some of the most common uses of real-time operating systems.

What are the advantages of a real-time operating system?

Real-time operating systems have better memory allocation and consumption than general-purpose operating systems. They also are error-free and can be embedded into systems.

What are the disadvantages of a real-time operating system?

Real-time operating systems are highly expensive and are complex and difficult to program for.

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