Firmware
What is RTOS?
Real-Time Operating System
A real-time operating system (RTOS) is a compact OS that schedules tasks with deterministic timing, guaranteeing time-critical operations meet deadlines.
An RTOS lets firmware juggle many concurrent tasks predictably — essential for motor control, communications, and safety systems. Common choices include FreeRTOS and Zephyr.
How an RTOS works
A real-time operating system schedules tasks by priority so that the most urgent work always runs within a known worst-case time. It provides tasks (threads), queues, semaphores, mutexes, timers and event flags, and usually a small memory footprint of a few kilobytes to tens of kilobytes.
RTOS vs bare metal vs Linux
Bare-metal firmware is a single loop with interrupts; it suits simple devices. An RTOS suits products that juggle several concurrent jobs, such as a radio stack, sensor sampling and a UI, with timing guarantees. Linux suits rich applications on MPUs but is not hard real-time without extra work.
Common RTOS choices
FreeRTOS is small, MIT-licensed and supported by most MCU vendors. Zephyr is a Linux Foundation project with a large driver and networking ecosystem. Commercial options such as SAFERTOS, QNX, VxWorks and embOS are used where safety certification or vendor support matters; Eclipse ThreadX (MIT-licensed since 2024) is an open-source option with safety-certification heritage.
RTOS FAQ
- What does RTOS stand for?
- RTOS stands for real-time operating system.
- Zephyr or FreeRTOS?
- FreeRTOS is simpler and smaller; Zephyr brings more drivers, networking and a unified devicetree/Kconfig build. See our Zephyr vs FreeRTOS white paper for a detailed comparison.