Difference Between RTOS and OS

An operating system (OS) is a system software that manages the computer hardware and software, and it provides services and functionality to programs and users. A real-time operating system (RTOS) is a segment of an operating system that is designed to provide predictable and deterministic behavior for time-critical applications. While RTOS and general-purpose OS have certain similarities, they also have some major differences.

Read this article to find out more about RTOS and OS and how they are different from each other.

What is a Real-Time Operating System?

A real-time operating system (RTOS) is a type of operating system that is intended to provide real-time behavior while adhering to strict timing limitations for time-critical applications. It focuses on ensuring important tasks are completed on time, which results in deterministic and predictable behavior. Let's get into the details of an RTOS −

Real-Time Behavior

• Determinism − An RTOS ensures that tasks are completed within time limits, known as deadlines. It has deterministic behavior, which means that its response time is predictable and consistent.

• Time Constraints − RTOSs differentiate between hard and soft real-time tasks. Hard real-time tasks have strict deadlines, and failure to meet them might result in system failure or safety risks. Soft real-time tasks have more flexible deadlines, and failing to meet them may result in reduced system performance but is not fatal.

Task Scheduling

• Preemptive Scheduling − Preemptive scheduling is used by RTOSs, which permits higher-priority processes to interrupt lower-priority tasks. When a higher-priority task is ready, it takes precedence over the present task, ensuring that vital tasks receive immediate attention.

• Priority-Based Scheduling − In an RTOS, tasks are prioritized, with higher-priority tasks receiving greater CPU time. The scheduler ensures that tasks with the highest priority are completed first, allowing for a quick response to time-critical events.

• Scheduling Algorithms − Rate monotonic scheduling (RMS), earliest deadline first (EDF), and fixed-priority scheduling are all common scheduling algorithms used in RTOSs. These algorithms prioritize tasks based on their deadlines and help with efficiently meeting real-time requirements.

Resource Management

• Interrupt Handling − RTOSs provide effective interrupt handling systems, allowing important processes to respond promptly to external events. Interrupt service routines (ISRs) are designed to execute with minimal overhead, ensuring that time-critical events are handled promptly.

• Fast Context Switching − Context switching is the process of preserving and restoring a task's state while switching tasks. RTOSs optimize context switching to reduce time between processes, allowing for faster response times and lower latency.

Services and Features

• Timers and Clocks − RTOSs provide precise timing services, such as timers and clocks, to correctly plan periodic tasks or events.

• Communication and Synchronization − Inter-task communication techniques such as message forwarding, shared memory, and event flags are provided by RTOSs, allowing processes to synchronize and communicate data efficiently.

• Power Management − Some RTOSs have power management tools to optimize energy use, particularly on devices that are battery-powered or have limited resources.

Application Domains

Timing, determinism, and real-time performance are important in fields such as aerospace and defence systems, automotive systems, industrial automation, medical devices, robotics, and telecommunications.

Popular real-time operating systems (RTOSs) include FreeRTOS, VxWorks, QNX, eCos, and RT-Linux.

What is an Operating System (OS)?

An operating system (OS) is an application of software that acts as a bridge between computer hardware and software applications. It maintains system resources, serves as a user and application interface for interacting with the computer, and coordinates the execution of numerous tasks. The following offer extensive explanations of the key aspects of an operating system −

Process and Task Management

• Process Creation and Control − Processes, which are instances of running programs, are created and managed by the operating system. It allocates system resources to processes, schedules their execution, and allows them to communicate and synchronize with one another.

• Multitasking − A multitasking operating system allows numerous processes or tasks to operate concurrently on a single computer. It uses scheduling algorithms to allocate CPU time to various programs, creating the illusion of parallel operations.

• Process Synchronization − Semaphores, mutexes, and condition variables are among the techniques provided by the operating system that allow processes to synchronize their actions. These techniques ensure that shared resources are safely accessed and that conflicts are avoided.

Memory Management

• Memory Allocation − The operating system maintains the memory resources of the computer, assigning memory to processes and applications. It monitors memory availability, assigns memory blocks to processes, and handles memory deallocation when processes stop.

• Virtual Memory − Virtual memory is a feature of many current operating systems that allows processes to access more memory than is physically accessible. Virtual memory provides processes with a consistent address space and enables effective memory management and protection.

File System Management

• File Organization − The operating system includes a file system for organizing and managing data on storage devices such as hard drives or solid-state drives. It defines a hierarchical structure of folders and files that users and applications can use to store, retrieve, and alter data.

Device Management

• Device Drivers − Device drivers allow the operating system to communicate with numerous hardware devices, such as keyboards, mice, printers, and network interfaces. These drivers convert OS requests into commands accepted by the devices, allowing communication and control.

• Input/Output (I/O) Management − The operating system controls input and output operations, ensuring that data is delivered correctly between devices and processes. It handles buffering, queuing, and scheduling of I/O requests and provides a standardized interface for applications to perform I/O operations.

User Interface

• Command-Line Interface (CLI) − Some operating systems provide a text-based interface through which users can interact with the system by typing instructions. The operating system interprets these commands and executes the desired operations.

• Graphical User Interface (GUI) − Many current operating systems include a graphical user interface (WIMP) that makes use of windows, icons, menus, and pointers. GUIs improve user friendliness and allow interaction through mouse clicks and gestures.

Difference Between RTOS and OS

The following table highlights the major differences between RTOS and OS −

Characteristics	RTOS	OS
Complexity	Lightweight and designed for minimal overhead and reduced complexity.	More complex, supporting a wide variety of applications and hardware configurations.
Application Domain	Commonly used in domains where timing and determinism are critical, such as aerospace, automotive, industrial control systems, medical devices, and robotics.	Suitable for a broader range of applications, including desktop computers, servers, mobile devices, and consumer electronics.
Examples	FreeRTOS, VxWorks, QNX, eCos, and RT-Linux	Windows, macOS, Linux, and Unix variants
Resource Utilization	Optimized for minimal resource usage and efficient memory management.	Optimized for efficient resource utilization and user experience
Cost	High Cost	Low Cost
Determinism	Deterministic execution with guaranteed timing and deadlines	Non-deterministic execution with no guarantees of timing or deadlines
Real-Time Behavior	Provides deterministic behavior	Primarily focuses on multitasking and resource sharing.

Conclusion

The ability to handle real-time tasks differentiates a real-time operating system (RTOS) from a general-purpose operating system (OS).

An RTOS is designed to provide predetermined behavior, ensuring that important tasks are completed within specified time constraints or deadlines. It optimizes real-time performance by using priority-based preemptive scheduling, efficient resource management, and specialised techniques. In industries where timing and determinism are essential, such as aerospace, automotive, and industrial control systems, RTOSs are often used.

Finally, the choice between an RTOS and a general-purpose OS depends on the application's specific requirements. An RTOS is usually the best solution when time and determinism are important, whereas a general-purpose OS is best for applications that require flexibility, multitasking, and a wide range of features.