Comparison of real-time operating systems

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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 Official website
Apache Mynewt Apache 2.0 open source embedded active ARM Cortex-M, MIPS32, Microchip PIC32, RISC-V
Arm OS Apache 2.0 Cortex-M, Cortex-R, Cortex-A
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 Mixed, 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 Digital Research
Concurrent DOS,
became Multiuser DOS
Proprietary closed defunct 8086, 286, 386, 68000, (also 8080/Z80 in dual-processor variants) Digital Research
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, MIPS
DioneOS Proprietary available for licensee embedded MSP430, MSP430x
(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 ? ? ? defunct TI-980A minicomputer ?
DSP/BIOS Free 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 Mixed, open source and commercial open source MCU, DSC, DSP SoC active R8C, M16C, PIC24, dsPIC33
eCos Modified GNU GPL open source embedded 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 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 Digital Research, Novell
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
FunkOS modified Sleepycat License embedded AVR, MSP430, Cortex-M3
HeartOS Proprietary closed safety critical x86, PowerPC, ARM
Huawei LiteOS BSD open source embedded active ARM (M0/3/4/7, A7/17/53, ARM9/11), x86, RISC-V
IBM 4680 OS Proprietary closed general purpose, industrial, POS defunct 286 IBM (DR Concurrent DOS 286 derivative)
IBM 4690 OS Proprietary active 286, 386 IBM (DR FlexOS 286/386 derivative)
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 ? ? ?
KolibriOS GNU GPL open source embeddable active x86
LynxOS Proprietary source available embedded Motorola 68010, x86/IA-32, ARM, Freescale PowerPC, PowerPC 970, LEON
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 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 Digital Research
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 Digital Research/Novell, Concurrent Controls, Datapac, IMS (see REAL/32)
Nano-RK Mixed open source embedded, WSN active AVR, MSP430
Neutrino Proprietary some source provided microkernel 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 Mixed, open source and commercial specification engine control units Various (mostly Automotive) vendors implemented and distribute/sell OSEK
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 ?
QNX Proprietary ? general purpose, medical devices active IA-32, AMD64-32, MIPS, PowerPC, SH-4, ARM, ARM64, StrongARM, XScale
QP Dual, open source and 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 IMS (Multiuser DOS derivative)
Real-time Linux (CONFIG_RT_PREEMPT) GNU GPLv2 open source general purpose same as Linux,,
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 ja:REX OS
RIOT GNU LGPL open source active ARM, MSP430, AVR, x86, RISC-V
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

rodos download
RSX-11 Proprietary ? ? historic PDP-11 n/a
RT-11 Proprietary ? general purpose defunct PDP-11 n/a
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 modified GNU GPL embedded ARM, Blackfin, ColdFire, TI C3x/C4x, H8/300, x86, 68k, Milkymist SoC, MIPS, Nios II, PowerPC, SuperH, SPARC, ERC32, LEON, Mongoose-V
RTLinux GNU GPL general purpose inactive same as Linux Official vendor Wind River 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 RTX64 RTOS, Real-Time Solutions for Windows 10 IoT (
RX116 ? ? embedded, industrial defunct NEC V20, NEC V30, NEC V40, NEC V50 first ITRON 1 compatible 16-bit RTOS
RX616 ? ? safety critical, embedded, industrial NEC V60, NEC V70 32-bit ITRON compatible
RX-UX832 ? ? embedded, industrial, general-purpose NEC V60, NEC V70 32-bit Unix-like RTOS
SafeRTOS Proprietary source code & Design Assurance Pack available embedded, safety critical active Same as FreeRTOS Same as FreeRTOS
SHaRK GNU GPL open source ? inactive ?
Simulink Real-Time Proprietary closed real-time testing-embedded active x86
SINTRAN III ? ? ? ? Norsk Data computers n/a
Symbian OS Eclipse open source embedded defunct ARM
T-Kernel T-License source available embedded RTOS active ARM, MIPS, SH, more
THEOS ? ? ? ? ?
ThreadX Proprietary partial source available ? 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
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
u-velOSity Proprietary ? microkernel active ?
velOSity ? ? ? 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[1][2]
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 embedded inactive-beta ?
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


  1. ^ "Windows Processor Requirements".
  2. ^ "Windows for Internet of Things (IoT) Platforms & Applications". Microsoft Windows for Business.

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