What is a real-time operating system (RTOS)?

These systems are crucial in applications like industrial automation, robotics, medical devices, and embedded systems where delays or failures can have severe consequences. Real-time operating systems are also commonly used in high-stakes environments (e.g., aerospace and defense) where real-time responses are essential for safety and performance.

A general-purpose operating system (GPOS) and a real-time operating system (RTOS) both coordinate system hardware resources (e.g., CPU, memory, I/O devices, storage), yet they differ significantly in their focus and capabilities.

Operating systems—such as Microsoft Windows, Linux and Unix—focus on maximizing overall system efficiency and supporting multitasking, but they rely on non-deterministic scheduling. As non-real-time systems, they may not always complete tasks on time, particularly under heavy load or in virtual machine (VM) environments where resources are shared.

In contrast to a general-purpose OS, a real-time OS is designed for real-time applications and guarantees that tasks meet strict timing requirements, often within microseconds. The resources in a real-time system are managed with deterministic scheduling to ensure that high-priority tasks are completed within specific time frames, even under load. While an RTOS can support VMs, the overhead of virtualization may impact its ability to meet real-time demands.

Real-time operating systems began developing in the 1960s and 1970s to meet the needs of time-sensitive applications, primarily in the military, aerospace and industrial sectors. Traditional operating systems weren’t designed for predictable, fast responses, so real-time operating systems were created to ensure tasks met strict deadlines that could handle external events with minimal delay. Key innovations during this time included preemptive scheduling algorithms and improvements in task prioritization and interrupt handling.

In the 1980s and 1990s, commercial RTOS products (e.g., VxWorks, QNX) became widely used, particularly in industries like telecommunications, automotive and embedded systems. Standardization efforts like the POSIX real-time extensions helped unify the design of real-time operating systems. In the 2000s, the growth of the Internet of Things (IoT) and embedded systems led to the popularity of lightweight real-time operating systems, such as FreeRTOS.

Today, real-time operating systems play a critical role in ensuring reliable, real-time operation in a wide range of apps, from medical devices to industrial control systems tied to critical infrastructure. Additionally, many real-time operating systems are incorporating artificial intelligence (AI) and machine learning (ML) to handle more dynamic, adaptive and complex systems. For instance, an AI-enabled RTOS can analyze data patterns, predict failure and optimize task scheduling in real-time based on system conditions.

The RTOS market size was estimated at 5.97 (USD Billion) in 2024. Moreover, the market is expected to grow from 6.41 (USD Billion) in 2025 to 12.21 (USD Billion) by 2034, exhibiting a compound annual growth rate (CAGR) of 7.41% during the forecast period (2025 - 2034).¹

Key features of a real-time operating system (RTOS) include the following:

• Determinism: An RTOS guarantees tasks are executed within a predictable, fixed time frame, which is essential for time-sensitive applications.

• Multitasking: Multitasking in a RTOS involves scheduling and managing multiple tasks, determining the order in which tasks are executed, and switching between them rapidly, giving the impression of parallel execution. 

• Memory management: An RTOS prevents tasks from interfering with each other’s memory space, improving system stability and security.

• Minimal latency: An RTOS reduces response time to external events or interrupts, ensuring quick reactions in real-time environments and minimizing interrupt latency. Efficient context switching in an RTOS further minimizes task-switching latency, allowing tasks to be quickly swapped in and out of the CPU, which reduces delays between executions and enhances overall system responsiveness.

• Priority-based scheduling: An RTOS executes higher-priority tasks before lower-priority ones, making sure critical tasks are handled first.

• Resource allocation: An RTOS efficiently handles memory allocation, processing power and other system resources to support real-time performance.

• Interrupt handling: An RTOS quickly and efficiently responds to hardware or software interrupts using RTOS application programming interface (API) mechanisms. This capability minimizes the time spent handling interrupts and ensures real-time task completion.

• Task synchronization: An RTOS provides inter-task communication (ITC) with mechanisms like semaphores and message queues to synchronize tasks and ensure safe sharing of resources among multiple tasks.

There are three main types of real-time operating systems (RTOSes), each designed to handle varying levels of timing precision (often in milliseconds) and tolerance for missed deadlines:

• Hard real-time operating systems

• Firm real-time operating systems

• Soft real-time operating systems

Hard real-time operating systems are designed with strict timing constraints for when meeting deadlines is crucial. Any failure to meet a deadline can have severe consequences, making reliability paramount. Common applications of hard real-time operating systems include aerospace, robotics and industrial control systems. To meet these stringent requirements, file systems in hard real-time systems are often streamlined to reduce overhead, ensuring that data is accessed or written within the strict timing constraints.

Firm real-time operating systems typically require meeting deadlines, but they can tolerate occasional delays without causing significant issues. Examples of such systems include multimedia playback, networking and certain industrial automation applications.

Soft real-time operating systems focus on timely execution, but missing a deadline does not have critical consequences. The system can still function properly, albeit with reduced performance. Examples include desktop operating systems, web servers and some office automation tools.

A real-time operating system (RTOS) offers numerous key benefits, making it ideal for critical, resource-constrained applications:

• Reliability and predictability

• Minimal overhead

• Fault tolerance

• Enhanced system efficiency

• Improved safety

• Scalability

• System stability

Real-time operating systems are used in a variety of industries where precise timing, reliability and predictable behavior are essential for critical applications:

• Aerospace

• Robotics

• Industrial control systems

• Healthcare devices

• Automotive systems

• Telecommunications

• Defense and military

Real-time operating systems are utilized in aerospace systems for flight control, navigation and mission-critical applications where timing precision is essential. Using high-performance computing (HPC), these critical systems can process complex data from various sensors in real time, ensuring quick, accurate responses that are crucial for safety and performance.

In robotics, real-time operating systems ensure the real-time control of robotic movements, sensor processing and communication. These systems need to operate with high precision and low latency, especially in industrial automation, medical robots and autonomous vehicles.

An RTOS is commonly applied in industrial control systems, such as manufacturing processes, plant automation and assembly lines. These systems require tight timing constraints to monitor sensors and other equipment in real time.

An RTOS is used in medical devices like pacemakers, infusion pumps and diagnostic equipment, where timely and predictable operation is necessary to ensure patient safety and device reliability.

In automotive applications, real-time operating systems support critical functions—such as autonomous driving systems and advanced driver-assistance systems (ADAS)—where safety and responsiveness are key.

An RTOS is essential in telecommunications infrastructure, including mobile base stations and satellite communication systems, where real-time processing and low-latency performance are necessary for maintaining stable and fast connections.

An RTOS is used in defense and military applications for radar systems, weapons control and surveillance systems, where operational accuracy and speed are crucial to establishing mission success and safety.

These popular real-time operating systems (RTOSes) are designed to meet the specific needs of various industries. They are optimized to run on processors like Intel and ARM, ensuring high performance, reliability and efficiency across diverse applications:

• VxWorks: This highly reliable RTOS, used in aerospace, defense and industrial automation, is known for its scalability, security and safety features.

• QNX: This modular, POSIX-compliant RTOS is favored in automotive, medical and industrial sectors, offering reliability and fault tolerance 

• FreeRTOS: This open-source, lightweight RTOS is ideal for embedded systems, microcontrollers, IoT devices and consumer electronics, emphasizing simplicity and efficiency.

• RTEMS: This open-source RTOS is designed for high-performance embedded systems, commonly deployed in aerospace, telecommunications and robotics applications.

• embOS: This compact RTOS is known for its scalability and deterministic performance, and it is often used in industrial and medical systems where reliability is key.

• Zephyr: This open-source, scalable RTOS from the Linux Foundation is optimized for small, resource-constrained devices, such as IoT gadgets and wearables.

• ThreadX: This high-performance RTOS, known for its minimal footprint and efficient resource management, is frequently used in consumer electronics, automotive and industrial systems.