Comparison of real-time operating systems

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Short description: none

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

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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)
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
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 | MSP430, MSP430x
DNIX | Proprietary | closed | general purpose | defunct | 68000
Embox  | BSD | open source  | embedded  | active  | x86, ARM, Microblaze, SPARC, PPC, MIPS
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.
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 | 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 | 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
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 | 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 | active | 286, 386
INTEGRITY | Proprietary | embedded | ARM, XScale, Blackfin, ColdFire, MIPS, PowerPC, x86
INtime | Proprietary | 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 | 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 | abandoned [1] | Arm Cortex-M
MenuetOS | GNU GPL | open source | active | ? | 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 | active | x86, ARM, PowerPC, MIPS, RISC-V[2]
MP/M | Proprietary | closed (meanwhile: open source) | general purpose, industrial | defunct | 8080, Z80, 8086
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 | 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 | 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 | 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)[3]
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 | 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-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
SuperTinyKernel RTOS | MIT | open source | embedded, IoT, safety critical | active | ARM Cortex-M (ARMv6-M through ARMv8.1-M: M0, M3, M4, M7, M33, M55), RISC-V (RV32I, RV32E), x86 (Simulator mode)
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 | embedded, IoT, safety critical | 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 | 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
μITRON | T-License | open source | embedded | active | ARM, MIPS, x86, Renesas RX100-200-600-700-others
μ-velOSity | Proprietary | ? | microkernel | active | ?
velOSity | Proprietary | ? | ? | 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 | 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

## References

1. ↑ "Important Update on Mbed" (in en). https://os.mbed.com/blog/entry/Important-Update-on-Mbed/.
2. ↑ "MontaVista Unveils CGX 5.0 – An AI-Ready Embedded Linux Platform Secured by Design" (Press release). San Jose, CA: MontaVista. April 9, 2024. Retrieved June 26, 2026.
3. ↑ 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
* Timing Comparison of the Real-Time Operating Systems for STM32 Microcontrollers (FreeRTOS, RT-Thread, RTX, uC/OS-II, uC/OS-III) - Symmetry in 2020

* v
* t
* e

Real-time operating systems (RTOS)

* Comparison of real-time operating systems

Open-source|

* BeRTOS
* ChibiOS/RT
* Contiki
* eCos
* ERIKA Enterprise
* FreeRTOS
* Fuchsia
* FunkOS
* Mynewt OS
* Nano-RK
* NuttX
* RIOT
* RTAI
* RTEMS
* RTLinux
* RT-Thread
* seL4
* TI-RTOS
* TRON
* Wombat OS
* Xenomai
* Zephyr

Proprietary|

* 4690 OS
* DioneOS
* embOS
* Integrity
* Junos OS
* LynxOS
* µC/OS-II
* MQX
* Nucleus RTOS
* OpenComRTOS
* OSE
* OS-9
* OS2000
* PikeOS
* QNX
* REAL/32
* REX OS
* ScreenOS
* ThreadX
* TPF
* VRTX
* VxWorks
* Windows Embedded Compact

Historic|

* 4680 OS
* Concurrent DOS
* DNIX
* DSOS
* EROS
* FlexOS
* MERT/UNIX-RT
* Multiuser DOS
* pSOS
* RMX
* RSX-11
* RT-11
* Sintran III
* Symbian
* THEOS
* UNOS

* Category

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