Comparison of real-time operating systems

Last updated November 30, 2024

This is a list of real-time operating systems (RTOSs). This is an operating system in which the time taken to process an input stimulus is less than the time lapsed until the next input stimulus of the same type.

Name	License	Source model	Target uses	Status	Platforms
Apache Mynewt	Apache 2.0	open source	embedded	active	ARM Cortex-M, MIPS32, Microchip PIC32, RISC-V
BeRTOS	Modified GNU GPL	open source	embedded	archived	ARM, Cortex-M3, ARM ARM7TDMI, Atmel AVR, PowerPC (emu), x86 (emu), x86-64 (emu)
CapROS	GNU GPL	open source	embedded	active	IA-32, ARM9
ChibiOS/RT	Dual, GNU GPL or proprietary	open source	embedded, small footprint	active	x86, ARM7, ARM9, Cortex-M0-M3-M4, PowerPC e200z, STM8, STM32, AVR, MSP430, ColdFire, H8S
ChorusOS	?	?	?	defunct	SPARC, x86, PowerPC
Concurrent CP/M, became MP/M	Proprietary	closed (meanwhile: open source)	general purpose, industrial	historic	8080, Z80, 8086
Concurrent DOS, became Multiuser DOS	Proprietary	closed	general purpose, industrial	defunct	8086, 286, 386, 68000, (also 8080/Z80 in dual-processor variants)
Contiki	BSD	open source	embedded, WSN	active	MSP430, AVR, ARM
Data General RDOS	Proprietary	?	general purpose	defunct	Data General Nova, Data General Eclipse
Deos	Proprietary	closed	safety critical	active	x86, PowerPC, ARM, MIPS
DioneOS	Proprietary	available for licensee	embedded	active	MSP430, MSP430x
DMERT (Duplex Multi-Environment Real-Time)	Proprietary(Bell Labs)	closed	OS for long-distance telephone switching systems	inactive	Bell Labs 3B20D (a proprietary, VAX-like system with redundant [duplex] processors)
DNIX	Proprietary	closed	general purpose	defunct	68000
GEC DOS	Proprietary	closed	process control	defunct	GEC 4000 series
DSOS	Proprietary	closed	?	defunct	TI-980A minicomputer
DSP/BIOS	Proprietary	closed, available with license	general purpose	maintenance only	Mostly Texas Instruments C2800, C5500, C6000 and OMAP DSP cores. Replaced by TI-RTOS, but available for download.
DSPnano RTOS	Proprietary	open source	MCU, DSC, DSP SoC	active	R8C, M16C, PIC24, dsPIC33
eCos	Modified GNU GPL	open source	embedded	inactive	ARM-XScale-Cortex-M, CalmRISC, 680x0-ColdFire, fr30, FR-V, H8, IA-32, MIPS, MN10300, OpenRISC, PowerPC, SPARC, SuperH, V8xx
eCosPro	Modified GNU GPL or eCosPro license	open source with non-free portions	embedded	active	ARM7-9, Cortex-A5-A9-M3-M4-M7, 680x0-ColdFire, H8-H8S, IA-32, MIPS32, MIPS64, microMIPS, NIOS II, OpenRISC, PowerPC, SPARC, SH4/4A, TILE-Gx, XScale
embOS	Proprietary	closed, available to customers, free object code for non-commercial use	embedded, industrial, IoT, safety critical	active	ARM7/9/11, ARM Cortex-A/R/M, AVR, AVR32, C16x, CR16C, ColdFire, H8, HCS12, M16C, M32C, MSP430, NIOS2, PIC18/24/32, R32C, R8C, RISC-V, RL78, RH850, RX100/200/600/700, RZ, SH2A, STM8, ST7, V850, 78K0, 8051
ERIKA Enterprise	GPL and GPL linking exception	open source	embedded	active	ARM7, ARM Cortex-M, ARM Cortex-A (on Jailhouse hypervisor), Hitachi H8, Altera Nios2, Microchip dsPIC (including dsPIC30, dsPIC33, and PIC24), Microchip PIC32, ST Microelectronics ST10, Infineon C167, Infineon Tricore, Freescale PPC e200 (MPC 56xx) (including PPC e200 z0, z6, z7), Freescale S12XS, EnSilica eSi-RISC, AVR, Lattice Mico32, MSP430, Renesas RX200, x86-64 (on Jailhouse hypervisor)
EROS	Modified GNU GPL	open source	experimental research use	dormant	IA-32
FlexOS	Proprietary	closed	general purpose, industrial, POS	defunct	186, 286, 386, V60, V70, 68000
Flexible Safety RTOS	Proprietary	closed, available to customers	embedded, safety critical	active	Altera/Intel NIOS II, ARM9, ARM Cortex-M, ARM Cortex-R, ARM Cortex-A, Infineon TriCore, Infineon AURIX, NXP ColdFire, NXP Kinetis, NXP PowerPC e200, NXP QorIQ, STMicroelectronics STM32, Xilinx/AMD MicroBlaze
FreeRTOS	MIT	open source	embedded	active	ARM, AVR, AVR32, ColdFire, ESP32, HCS12, IA-32, Cortex-M3-M4-M7, Infineon XMC4000, MicroBlaze, MSP430, PIC, PIC32, Renesas H8/S, RISC-V, RX100-200-600-700, 8052, STM32, TriCore, EFM32
Fuchsia	Varies	open source	embedded		AArch64, x86-64
Keil RTX	Apache 2.0	open source	embedded		Arm Cortex-M
FunkOS	Modified Sleepycat License	open source	embedded		AVR, MSP430, Cortex-M3
HeartOS	Proprietary	closed	safety critical		x86, PowerPC, ARM
Huawei LiteOS	BSD	open source	embedded	defunct	ARM (M0/3/4/7, A7/17/53, ARM9/11), x86, RISC-V
HarmonyOS	Proprietary	closed	embedded	active	AArch64, x86-64, RISC-V, LingxiISA
IBM 4680 OS	Proprietary	closed	general purpose, industrial, POS	defunct	286
IBM 4690 OS	Proprietary		general purpose, industrial, POS	active	286, 386
INTEGRITY	Proprietary		embedded		ARM, XScale, Blackfin, ColdFire, MIPS, PowerPC, x86
INtime	Proprietary		embedded		x86
ITRON	T-License	varies	embedded		ARM, MIPS, x86, Renesas RX100-200-600-700-others
Kaspersky OS	Proprietary	open source	safety critical, virtualization		x86, x86_64, ARMV5, ARMV7, ARMV8, MIPS32
KolibriOS	GNU GPL	open source	embeddable		x86
LynxOS	Proprietary	source available	embedded		Motorola 68010, x86/IA-32, ARM, Freescale PowerPC, PowerPC 970, LEON
Mbed OS	Apache 2.0	open source	embedded		Arm Cortex-M
MenuetOS	GNU GPL	open source	?		IA-32
MERT	Proprietary(Bell Labs)	closed	OS for long-distance telephone switching systems	inactive	PDP-11
MicroC/OS-III	Apache 2.0	open source	embedded	active	ARM7-9-11/Cortex-M1-3-4-A8/9, AVR, HC11/12/S12, ColdFire, Blackfin, MicroBlaze, NIOS, 8051, x86, Win32, H8S, M16C, M32C, MIPS, 68000, PIC24/dsPIC33/PIC32, MSP430, PowerPC, SH, StarCore, Renesas RX100-200-600-700, RL; STM32, ...
MontaVista Linux	GNU GPL	open source	embedded	?
MP/M	Proprietary	closed (meanwhile: open source)	general purpose, industrial	defunct	8080, Z80, 8086
M-RTOS	Proprietary	closed	safety critical, embedded	active	PowerPC, ARM, MIPS
MQX	Proprietary	complimentary source available	embedded	active	Freescale Power, ColdFire, Kinetis Cortex ARM, List of Freescale products
Multiuser DOS	Proprietary	closed	general-purpose, industrial	defunct	386
Nano-RK	Dual, GPL or commercial	open source	embedded, WSN	defunct	AVR, MSP430
Neutrino	Proprietary	some source provided	microkernel, embedded, industrial	active	ARM, ARM64, MIPS, PPC, SH, x86, x86-64, XScale
Nucleus RTOS	Proprietary	source provided	embedded		ARM (Cortex-M3-M4-R4-R4F-A8-A9, ARM7-9-11), PowerPC, MIPS32-16e, microMIPS, ColdFire, SuperH
NUT	Proprietary	open source	embedded, industrial		ARM-M0, ARM-M0+, ARM Cortex-M3, ARM9, ARM Cortex-M7, Cortex-M3
Nut/OS	BSD	open source	embedded, industrial		AVR, AVR32, ARM7, ARM9, Cortex-M3
NuttX	Apache 2.0	open source	embedded, small footprint		Linux user mode, ARM7-9, Cortex-A5-A8-A9-M0-M3-M4-M7, 8052, Espressif ESP32, Lattice LM32, Renesas MC16C/26/SH-1, RISC-V, Zilog Z16F, Zilog eZ80 Acclaim!, Zilog Z8Encore!, Z80, MIPS PIC32MX, PIC32MZ
OpenComRTOS	Proprietary	source provided	embedded		Freescale PowerPC, Texas Instruments C66xxx DSP, ARM, XMOS, MicroBlaze, LEON, NXP CoolFlux DSP, Melexis MLX16, Win32, Linux
OS2000	Proprietary	?	embedded	active	MIPS (Baget variant), KOMDIV-32, KOMDIV-64, Intel BSPs (x86)
OS4000	Proprietary	closed	process control	maintenance only	GEC 4000 series
OSE	Proprietary	available to customers	general purpose	active	ARM, PowerPC, x86, TI OMAP, ...
OS-9	Proprietary	available to customers	embedded		ARM-strongARM, MIPS, PowerPC, SuperH, x86/Pentium, XSCALE, Motorola 6809, 680x0, SPARC
OSEK	Dual, GPL or commercial	specification	embedded		engine control units
Phoenix-RTOS	BSD	open source	embedded	active	ARMv7 Cortex-M, ARMv7 Cortex-A, IA-32, RISC V
PikeOS	Proprietary	available to customers	certifiable safety & security, embedded virtualisation	active	PPC, x86, ARM, MIPS, SPARC-LEON, RISC-V
Protothreads	BSD	open source	general purpose	active	Architecture independent
pSOS	Proprietary	?	?	discontinued	680x0
PX5 RTOS	Proprietary	royalty-free licensing	embedded	active	Embedded MCU and MPU architectures. ARM's Cortex-M, Cortex-R, Cortex-A, RISC-V. AMP and SMP configurations.
QNX	Proprietary	?	microkernel, embedded, industrial		active
QP	Dual, GPL or commercial	dual	MCU, DSC, DSP SoC		ARM7/9, ARM Cortex-M3-M0, MSP430, TMS320C28x, AVR, AVRXmega, ColdFire, 68HC08, M16C/R8C, H8, 8051, 80251, PIC18, PIC24/dsPIC33, Nios II, PSoC1
REAL/32	Proprietary	closed	general-purpose, industrial		386
Real-time Linux (PREEMPT RT)	GNU GPLv2	open source	general purpose		x86, x86_64, RISC-V, ARM64 and LoongArch (ARM and POWER in the -rt branch)^[1]
RedHawk Linux RTOS	Proprietary	closed	hardware-in-the-loop, software-in-the-loop, general purpose	active	Intel, AMD, ARM, NVIDIA Drive, NVIDIA Jetson Orin
REX OS	Proprietary	closed, available with license	embedded	inactive	ARM
RIOT	GNU LGPL	open source		active	ARM7, ARM Cortex M, MSP430, AVR, RISC-V, Xtensa
RMX	Proprietary	closed		defunct	Intel 8080, 8086, 80386, higher
RODOS	BSD	source provided		active	ARMv7 (M3, A8, A9), AVR32, PowerPC 405, SPARC64 Platforms: SmartFusion2, RaspberryPi, STM32 On an OS: Linux, Windows, macOS, FreeRTOS, RTEMS
RSX-11	Proprietary	?	?	historic	PDP-11
RT-11	Proprietary	?	general purpose	defunct	PDP-11
RTAI	GNU GPL	open source	general purpose	active	x86 (with and without FPU and TSC), x86-64, PowerPC, ARM (StrongARM; ARM7: clps711x-family, Cirrus Logic EP7xxx, CS89712, PXA25x), m68k (supporting both MMU and NOMMU cpus)
RTEMS	BSD		embedded	active	AArch64, ARM, Blackfin, ColdFire, TI C3x/C4x, H8/300, x86, x86_64, 68k, Microblaze, Milkymist SoC, MIPS, Nios II, PowerPC, SuperH, SPARC, ERC32, LEON, Mongoose-V
RTLinux	GNU GPL		general purpose	inactive	same as Linux
RT-Kernel	Proprietary	source provided	embedded	active	ARM, Blackfin
RT-Thread	Apache 2.0	open source	embedded	active	ARM, ARM Cortex-M0-M3-R4-M4-M7, IA-32, AVR32, Blackfin, nios, PPC, M16C, MIPS (loongson-1b-1c, PIC32，xburst), MicroBlaze, V850, unicore32,
RTXC Quadros	Proprietary	source available	embedded		ARM - Atmel/Freescale/NXP/ST/TI, Blackfin, 680x0-ColdFire, PowerPC, StarCore, TI-Luminary Stellaris, TI OMAP, XScale
RTX, RTX64	Proprietary	closed	MS Windows extension		x86, x86-64
RX116	?	?	embedded, industrial	defunct	NEC V20, NEC V30, NEC V40, NEC V50
RX616	?	?	safety critical, embedded, industrial		NEC V60, NEC V70
RX-UX832	?	?	embedded, industrial, general-purpose		NEC V60, NEC V70
SafeRTOS	Proprietary	source code & Design Assurance Pack available	embedded, safety critical	active	Same as FreeRTOS
SHaRK	GNU GPL	open source	?	inactive	?
Simulink Real-Time	Proprietary	closed	real-time testing-embedded	active	x86
SINTRAN III	Proprietary	?	?	?	Norsk Data computers
Symbian OS	Eclipse	open source	embedded	defunct	ARM
T-Kernel	T-License	source available	embedded RTOS	active	ARM, MIPS, SH, more
THEOS	Proprietary	?	?	?	?
ThreadX	MIT	open source	?	active	ARC, ARM/Thumb, AVR32, BlackFin, 680x0-ColdFire, H8-300H, Luminary Micro Stellaris, M-CORE, MicroBlaze, PIC24-dsPIC, PIC32, MIPS, V8xx, Nios II, PowerPC, Renesas RX100, RX200, RX600, RX700, Synergy, SH, SHARC, StarCore, STM32, StrongARM, TMS320C54x, TMS320C6x, x86/x386, XScale, Xtensa/Diamond, ZSP
TI-RTOS Kernel (SYS/BIOS)	BSD	open source	embedded	active	Mostly Texas Instruments: MSP430-432, C2000-5000-6000, TI's ARM families (Cortex M3-4F-R4-A8-A15), SimpleLink Wireless CC2xxx-CC3xxx
TizenRT	Apache 2.0	open source	embedded	active
Transaction Processing Facility	Proprietary	mixed	general purpose	active	IBM Z series
TRON project	Free	mixed	mixed	active	any: is a specification, not an implementation
UNIX-RTR	?	?	?	defunct	PDP-11
UNOS	?	?	?	historic	680x0
UniProton	Free	open source	embedded	active	AArch64 (Kunpeng), x86-64 on openEuler community & ARM, RISC-V, x86, x64 and LoongArch on OpenHarmony and Oniro OS as add-on kernel
μITRON	T-License	open source	embedded	active	ARM, MIPS, x86, Renesas RX100-200-600-700-others
μ-velOSity	Proprietary	?	microkernel	active	?
velOSity	Proprietary	?	?	active	Power ISA, ARM/XScale, MIPS, x86/Pentium, ColdFire, Blackfin, OMAP, DaVinci
VAXELN	Proprietary	closed source	?	historic	VAX
VRTX	Proprietary	?	?	superseded by Nucleus RTOS	ARM, MIPS, PowerPC, RISC
VxWorks	Proprietary	?	embedded	active	ARM, IA-32, Intel 64, MIPS, PowerPC, SH-4, StrongARM, xScale
Windows CE	Proprietary	Microsoft Shared Source			x86, MIPS, ARM, SuperH
Windows 10 IoT	Proprietary	?			Intel Atom, Celeron, Pentium; Qualcomm Snapdragon, Broadcom, NXP i.MX
Xenomai	GNU GPLv2	open source	general		x86, x86-64, PowerPC, ARM, Analog Devices Blackfin BF52x, BF53x, BF54x and BF56x
XINU	Free	open source	embedded	active	x86, MIPS, ARM, AVR
XMK	BSD	open source	embedded	inactive
Zephyr	Apache 2.0	open source	embedded	active	ARM (Cortex-M0, -M3, -M4, -M23, -M33, -R4, -R5, -A53), x86, ARC, RISC-V, Nios II, Xtensa, SPARC

Related Research Articles

Real-time computing (RTC) is the computer science term for hardware and software systems subject to a "real-time constraint", for example from event to system response. Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines".

A real-time operating system (RTOS) is an operating system (OS) for real-time computing applications that processes data and events that have critically defined time constraints. An RTOS is distinct from a time-sharing operating system, such as Unix, which manages the sharing of system resources with a scheduler, data buffers, or fixed task prioritization in multitasking or multiprogramming environments. All operations must verifiably complete within given time and resource constraints or else fail safe. Real-time operating systems are event-driven and preemptive, meaning the OS can monitor the relevant priority of competing tasks, and make changes to the task priority. Event-driven systems switch between tasks based on their priorities, while time-sharing systems switch the task based on clock interrupts.

An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.

QNX is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market.

pSOS is a real-time operating system (RTOS), created in about 1982 by Alfred Chao, and developed and marketed for the first part of its life by his company Software Components Group (SCG). In the 1980s, pSOS rapidly became the RTOS of choice for all embedded systems based on the Motorola 68000 series family architecture, because it was written in 68000 assembly language and was highly optimised from the start. It was also modularised, with early support for OS-aware debugging, plug-in device drivers, Internet protocol suite (TCP/IP) stacks, language libraries, and disk subsystems. Later came source code level debugging, multiprocessing support, and further computer networking extensions.

An Embedded Operating System (EOS) is an operating system designed specifically for embedded computer systems. These systems aim to enhance functionality and reliability to perform dedicated tasks. When the multitasking method employed allows for timely task execution, such an OS may qualify as a real-time operating system (RTOS).

The LynxOS RTOS is a Unix-like real-time operating system from Lynx Software Technologies. Sometimes known as the Lynx Operating System, LynxOS features full POSIX conformance and, more recently, Linux compatibility. LynxOS is mostly used in real-time embedded systems, in applications for avionics, aerospace, the military, industrial process control and telecommunications.

Blackfin is a family of 16-/32-bit microprocessors developed, manufactured and marketed by Analog Devices. The processors have built-in, fixed-point digital signal processor (DSP) functionality performed by 16-bit multiply–accumulates (MACs), accompanied on-chip by a microcontroller. It was designed for a unified low-power processor architecture that can run operating systems while simultaneously handling complex numeric tasks such as real-time H.264 video encoding.

FreeRTOS is a real-time operating system kernel for embedded devices that has been ported to 40 microcontroller platforms. It is distributed under the MIT License.

Eclipse ThreadX is a highly deterministic, embedded real-time operating system (RTOS) programmed mostly in the language C. Originally it was named ThreadX when Express Logic first developed it, later it was renamed to Azure RTOS after Express Logic was purchased by Microsoft, most recently it was renamed again to Eclipse ThreadX after it transitioned to open source model under the stewardship of the Eclipse Foundation.

TI-RTOS is an embedded tools ecosystem created and offered by Texas Instruments (TI) for use across a range of their embedded system processors. It includes a real-time operating system (RTOS) component-named TI-RTOS Kernel, networking connectivity stacks, power management, file systems, instrumentation, and inter-processor communications like DSP/BIOS Link. It is free and open-source software, released under a BSD license.

XtratuM is a bare-metal hypervisor specially designed for embedded real-time systems available for the instruction sets LEON2/3/4, ARM v7 and V8 processors and RISC-V processor.

TenAsys is a privately owned company providing real-time software and services based on the x86 Intel Architecture and Microsoft Windows operating system.

QP is a family of open source real-time embedded frameworks (RTEFs) and runtime environments based on active objects (actors) and hierarchical state machines. The QP family consists of the lightweight QP/C and QP/C++ frameworks, written in C (C99) and C++ (C++11), respectively.

OpenComRTOS is a commercial network-centric, formally developed real-time operating system (RTOS), aimed mainly at the embedded system market.

RT-Thread is an open-source real-time operating system (RTOS) for embedded systems and Internet of things (IoT). It is developed by the RT-Thread Development Team based in China. RT-Thread is aimed to change the current situation in China that there is no well used open-source real-time operating system in the microcontroller field.

Zephyr is a small real-time operating system (RTOS) for connected, resource-constrained and embedded devices supporting multiple architectures and released under the Apache License 2.0. Zephyr includes a kernel, and all components and libraries, device drivers, protocol stacks, file systems, and firmware updates, needed to develop full application software.

PX5 RTOS is a real-time operating system (RTOS) designed for embedded systems. It is implemented using the ANSI C programming language.

William (Bill) Lamie is an American software engineer. He is known as the author of the Nucleus, ThreadX and PX5 real-time operating systems (RTOS).

References

↑ PREEMPT_RT patch versions

External links

2024 RTOS Performance Report (FreeRTOS / ThreadX / PX5 / Zephyr) - Beningo Embedded Group
2013 RTOS Comparison (Nucleus / ThreadX / ucOS / Unison) - Embedded Magazine

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[1] PREEMPT_RT patch versions

[1]