What Is an RTOS?
A Real-Time Operating System (RTOS) is a software platform for real-time computing applications that process events and data with well-defined time constraints. Unlike general-purpose operating systems (GPOS), an RTOS must schedule processing and data sharing between applications on limited hardware resources. Typically, these applications respond to inputs within microseconds and run on small embedded devices with less than 1 MB of memory. In this section, you’ll learn more about what an RTOS is as well as RTOS types and architectures.
What An RTOS OS Does
An RTOS operating system manages processor cycles, memory, peripherals, and interrupts. Embedded developers use an RTOS when an application's real-time requirements or memory constraints make unsuitable a general purpose operating system, like Linux or Windows.
Difference between an RTOS and other OS?
Determinism, small footprint, quick response, concurrent jobs, safety, and security are key aspects of an RTOS.
- Determinism: An RTOS is deterministic if a given input always results in the same output, often by following the same control path through code.
- Minimal Footprint: The RTOS operates on resource-constrained platforms, so it must be able to be installed and run in a small memory footprint.
- Minimal latency: The RTOS responds quickly to external events, often executing tasks within fractions of a second.
- Concurrency: The RTOS executes multiple jobs simultaneously, using schedulers to avoid resource contention.
- Safety and security: While not essential, many RTOSes include functional safety and cybersecurity features and are pre-certified to demonstrate support for industry best practices.
RTOS Types
There are three types of RTOSes as classified by levels of responsiveness. They are used in different types of embedded systems:
- A hard RTOS is used in systems that have strict timing requirements where tasks must be completed within a guaranteed time frame to ensure proper functioning. Examples include automotive cruise control and railway signaling systems.
- A firm RTOS is used in systems with a combination of tasks with deadlines that must be met and those that can tolerate occasional misses. Examples include robotic assembly lines and telecommunications networks.
- A soft RTOS is used in systems that have flexibility in meeting task deadlines, such as in-flight entertainment and voice chat apps.
RTOS Architectures
Two categories of RTOS architectures are monolithic kernel and microkernel.
- A monolithic kernel RTOS puts all OS components and operating processes in the same memory space, which makes it faster.
- A microkernel RTOS keeps core functions separate from application-specific functions, which makes it more modular, fault tolerant, and cybersecure.