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What is a Real-Time Operating System (RTOS)?
A real-time operating system (RTOS) is a type of computer operating system (OS) designed for specific tasks that need to be completed quickly and predictably. Unlike standard operating systems (OS) like Windows, which are built for multitasking and ease of use, an RTOS focuses on doing things fast and on time.
Real-time operating systems are built for computing environments where numerous application operations need to be processed in a short time frame – often with a strict minimum or maximum time to complete the task. That makes RTOS suitable for applications like medical devices, industrial controls, and air traffic control systems.
Key Takeaways
- An RTOS is built for computing operations that need to be executed fast and on a precise schedule.
- That makes them different from standard operating systems like Windows or Linux, which are designed for general-purpose computing.
- An OS handles multiple applications at once, assigns bandwidth and processing power on a priority basis, and the speed of an operation can vary widely.
- That wouldn’t work in something like a pacemaker, which is where an RTOS comes in.
- It ensures that specific operations happen quickly, predictably, and within a strict time limit.
How Real-Time Operating System Works
An RTOS is designed for executing multiple, high-priority tasks simultaneously in a single batch. It ensures that computer processes respond to events within predictable time limits.
In an RTOS, operations are completed within defined time constraints and against a predefined set of task priorities. An RTOS can also update some task priorities based on pre-set variables.
What is the Purpose of RTOS?
A normal operating system like Windows or Linux is built for multitasking and making it easy for end users to manipulate software and data flexibly. A real-time operating system is built to handle time-sensitive tasks in a precise and predictable way.
An RTOS asserts real-time control over computer hardware resources like random access memory (RAM) to make sure they are reliable and responsive – even when a system experiences heavy use or changing conditions.
Types of RTOS
There are three types of real-time operating systems:
RTOS Characteristics
They can ensure that the same input will always result in the same output.
An RTOS is designed to be fast and responsive, executing operations in a fraction of the time a general OS would need.
Real-time operating systems are frequently used in systems where failure would mean catastrophes, such as medical devices or air traffic radar tracking systems.
Tasks given a high priority are executed first, and lower-priority tasks are handled later.
The size of an RTOS is typically measured in megabytes, often in single digits. A Windows 11 OS takes up more than 20 gigabytes.
RTOS vs. OS
- Simpler design
- Guaranteed response time
- Completes tasks under strict timing constraints
- Minimum and maximum bandwidth limits
- More predictable
- Complex design
- ‘Best effort’ response time
- Completes tasks on a fairness principle
- Aims for average bandwidth usage
- Less predictable
Real-Time Operating System Architectures
There are two prevailing approaches in RTOS design:
- Microkernel systems
In microkernel architecture, the operating system components are kept in separate sections and operate independently of the others. This means some operations take longer as individual actions need to be read and approved by the kernel before moving to a component for processing.
- Monolithic systems
In a monolithic system, components are stored together and direct interaction is allowed between them, making some operations faster. Monolithic kernels provide services of their own while also regulating services within components.
RTOS Examples
Examples of real-time operating systems include:
- Pacemakers
- Military hardware
- Airline traffic control systems
- Airline reservation systems
- Manufacturing process control systems
- Robotics
RTOS Use Cases
- A standard office inkjet printer is run by an RTOS that delivers the correct amount of ink though the print head and to a specific position on a piece of paper. If the operating systems were to miss a deadline in the processing of print tasks, the print job would fail.
- In 1997, the Mars Pathfinder came close to failure when a higher priority task wasn’t completed on time. The problem was corrected and the spacecraft was able to land on Mars successfully.
RTOS Pros and Cons
- An RTOS ensures maximum utilization of hardware and resources
- Time required to execute tasks is short, 3-4 microseconds on average
- Operations can be prioritized by importance and executed in sequence
- Small size means they can be embedded in smaller systems for transport and medical use
- System errors are vastly reduced and very rare
- RTOS algorithms can be complex and difficult for developers to alter or write to
- An RTOS requires specific device drivers and interrupt signals to respond quickly
- RTOS are less flexible than OS and only capable of minimal task switching
The Bottom Line
Real-time operating systems are essential for delivering computing capabilities with certainty. By definition they execute tasks in real time. That makes them ideal for applications where multiple operations need to be executed near-instantaneously, such as high-speed stock trading.
By providing real-time control over hardware and multitasking within set timescales, an RTOS guarantees smooth and predictable operation even during periods of heavy use.
