What is Microsoft Azure RTOS?

Azure RTOS is a real time operating system (RTOS) for Internet of Things (IoT) and edge devices powered by microcontroller units (MCUs). Azure RTOS is designed to support most highly constrained devices (battery powered and having less than 64 KB of flash memory).

Azure RTOS is pre-certified for a variety of safety standards. These include the IEC 61508 SIL 4, IEC 62304 Class C, and ISO 26262 ASIL D certifications.

Azure RTOS provides an EAL4+ Common Criteria security certified environment, including full IP layer security via IPsec and socket layer security via TLS and DTLS. Our software crypto library has achieved FIPS 140-2 certification. We also leverage hardware cryptographic capabilities, memory protection via ThreadX MODULES, and support for ARM's TrustZone ARMv8-M security features.

Components of Azure RTOS

The Azure RTOS platform is the collection of run-time solutions including Azure RTOS ThreadX, Azure RTOS FileX, Azure RTOS GUIX, Azure RTOS NetX, Azure RTOS NetX Duo, and Azure RTOS USBX.

Azure RTOS ThreadX

Azure RTOS ThreadX is an advanced Real-Time Operating System (RTOS) designed specifically for deeply embedded applications. Among the multiple benefits Azure RTOS ThreadX provides are advanced scheduling facilities, message passing, interrupt management, and messaging services. Azure RTOS ThreadX has many advanced features, including its picokernel architecture, preemption-threshold scheduling, event-chaining, and a rich set of system services.

Azure RTOS FileX

Azure RTOS FileX is a high-performance FAT-compatible file system. It is fully integrated with Azure RTOS ThreadX and is available for all supported processors. Like Azure RTOS ThreadX, Azure RTOS FileX is designed to have a small footprint and high performance, making it ideal for today's deeply embedded applications that require file operations. Azure RTOS FileX supports most physical media, including RAM disk, USBX, SD CARD, and NAND/NOR flash memories via Azure RTOS LevelX.


Azure RTOS GUIX is a professional quality graphical user interface package, created to meet the needs of embedded systems developers. Unlike the alternatives, Azure RTOS GUIX is small, fast, and easily ported to virtually any hardware configuration capable of supporting graphical output. Azure RTOS GUIX also delivers exceptional visual appeal and an intuitive and powerful API for application-level user interface development.

Azure RTOS NetX

Azure RTOS NetX is a high-performance implementation of TCP/IP protocol standards. It is fully integrated with Azure RTOS ThreadX, and is available for all supported processors. Azure RTOS NetX has a unique Piconet architecture. Combined with a zero-copy API, it makes it a perfect fit for today's deeply embedded applications that require network connectivity.

Azure RTOS NetX Duo

Azure RTOS NetX Duo is an advanced, Industrial Grade TCP/IP network stacks designed specifically for deeply embedded, real-time, and IoT applications. Azure RTOS NetX Duo is a dual IPv4 and IPv6 network stack, while NetX is the original IPv4 network stack, essentially a subset of Azure RTOS NetX Duo.


Azure RTOS USBX is a high-performance USB host, device, and On-The-Go (OTG) embedded stack. It is fully integrated with ThreadX and is available for all Azure RTOS ThreadX supported processors. Like Azure RTOS ThreadX, Azure RTOS USBX is designed to have a small footprint and high performance, making it ideal for deeply embedded applications that require an interface with USB devices.

Windows tools

Azure RTOS GUIX Studio provides a complete GUI application design environment, facilitating the creation and maintenance of all graphical elements in the application's GUI. Azure RTOS GUIX Studio automatically generates C code compatible with the Azure RTOS GUIX library, ready to be compiled and run on the target.

Azure RTOS TraceX is a host-based analysis tool that provides developers with a graphical view of real-time system events and enables them to visualize and better understand the behavior of their real-time systems.

The Azure RTOS Advantage

Azure RTOS provides the following advantages over other real-time operating systems.

Most deployed RTOS

Azure RTOS has over 6.2 billion deployments worldwide, according to the leading M2M market intelligence firm, VDC Research. The popularity of Azure RTOS is a testament to its reliability, quality, size, performance, advanced features, ease-of-use, and overall time-to-market advantages.

“We have followed the growth trajectory of THREADX in the wireless and IoT markets since the company’s founding, and are increasingly impressed by the widespread industry adoption of THREADX.” – Chris Rommel, Executive Vice President, VDC Research

Intuitive and consistent API design

  • Intuitive and consistent API.
  • Noun-verb naming convention.
  • All APIs have leading prefix, such as tx_ for ThreadX and fx_ for FileX, to easily identify the Azure RTOS component they belong to.
  • Functional consistency throughout the APIs. For example, all API functions that suspend have an optional timeout that functions in an identical manner.
  • Many APIs are directly available from application ISRs.
  • Optional user-notification callbacks for media and file operations.
  • Event-driven programming model (API).

High efficiency

  • Small code footprint.
  • Scalable code footprint based on the services used.
  • Pre-certified by TUV and UL to IEC 61508 SIL 4, IEC 62304 Class C, ISO 26262 ASIL D, and EN 50128 SW-SIL4.
  • Fast execution. Azure RTOS is designed for speed and has minimal internal function call layering to help achieve the fastest possible performance.

Fastest time-to-market

Azure RTOS is easy to install, learn, use, debug, verify, certify, and maintain. As a result, Azure RTOS is one of the most popular real time operating systems for embedded IoT devices, including many SoCs from Broadcom, Gainspan, and so forth. Our consistent time-to-market advantage is built on:

  • Complete source code availability.
  • Easy-to-use API.
  • Comprehensive and advanced feature set.
  • Quality documentation.

One Simple License

There is no cost to use and test the source code and no cost for production licenses when deployed to pre-licensed devices, all other devices need a license.

Full, highest-quality source code

Throughout the years, Azure RTOS source code has set the bar in quality and ease of understanding. In addition, the convention of having one function per file provides for easy source navigation.

Pre-certified by TUV and UL to many safety standards

Azure RTOS has been certified by SGS-TUV Saar for use in safety-critical systems, according to IEC-61508 SIL 4, IEC-62304 SW Safety Class C, ISO 26262 ASIL D and EN 50128. The certification confirms that Azure RTOS can be used in the development of safety-related software for the highest safety integrity levels of IEC-61508, IEC-62304, ISO 26262 and EN 50128 for the “Functional Safety of electrical, electronic, and programmable electronic safety-related systems.” SGS-TUV Saar, formed through a joint venture of Germany’s SGS-Group and TUV Saarland, has become the leading accredited, independent company for testing, auditing, verifying, and certifying embedded software for safety-related systems worldwide. The industrial safety standard IEC 61508, and all standards that are derived from it, including IEC-62304, ISO 26262 and EN 50128, are used to assure the functional safety of electrical, electronic, and programmable electronic safety-related medical devices, process control systems, industrial machinery, automobiles and railway control systems.

SGS-TUV certification

Azure RTOS has been recognized by UL for compliance with UL 60730-1 Annex H, CSA E60730-1 Annex H, IEC 60730-1 Annex H, UL 60335-1 Annex R, IEC 60335-1 Annex R, and UL 1998 safety standards for software in programmable components. UL is a global, independent, safety-science company with more than a century of expertise innovating safety solutions, ranging from the public adoption of electricity to breakthroughs in sustainability, renewable energy, and nanotechnology.

CRU UL certification

Artifacts (Certificate, Safety Manual, Test Report, etc.) associated with the TUV and UL certifications are available to license.

In cases where the application needs additional certification, a certification service is available through Microsoft for providing turn-key certification to various standards using the actual hardware platform and even covering the application code. Contact us for more details on our certification service.

EAL4+ Common Criteria security certification

Azure RTOS has achieved EAL4+ Common Criteria security certification. The Target of Evaluation (TOE) covers Azure RTOS ThreadX, Azure RTOS NetX Duo, Azure RTOS NetX Secure TLS, and Azure RTOS NetX MQTT. This represents the most typical IoT protocols required by deeply embedded sensors, devices, edge routers, and gateways.

EAL certification

The IT Security Evaluation Facility used for the Microsoft Azure RTOS SC security certification is Brightsight BV and the Certification Authority is SERTIT.

FIPS 140-2 Validated

Azure RTOS Crypto libraries have achieved Federal Information Processing Standardization 140-2 (FIPS 140-2) Certification for software, which specifies requirements for cryptography modules. FIPS 140-2 requires all federal government agencies and departments that use cryptographic-based security to meet specific standards related to encryption strength and capabilities. These cryptographic-based security standards are also recognized in Canada and the European Union.

The Information Security evaluation lab used for Azure RTOS Crypto libraries was atsec and the certification authority is The National Institute of Standards and Technology (NIST).

Azure RTOS on most popular 32/64-bit microprocessors, out-of-the-box, fully tested and fully supported, including the following advanced architectures.

  • Analog Devices: SHARC, Blackfin, CM4xx

  • Andes Core: RISC-V

  • Ambiqmicro: Apollo MCUs

  • ARM: ARM7, ARM9, ARM11, Cortex-M0/M3/M4/M7/A15/A5/A7/A8/A9/A5x 64-bi/A7x 64-bit/R4/R5, TrustZone ARMv8-M

  • Cadence: Xtensa, Diamond

  • CEVA: PSoC, PSoC 4, PSoC 5, PSoC 6, FM0+, FM3, MF4, WICED WiFi

  • Cypress: RISC-V

  • EnSilica: eSi-RISC

  • Infineon: XMC1000, XMC4000, TriCore

  • Intel; Intel FPGA: x36/Pentium, XScale, NIOS II, Cyclone, Arria 10

  • Microchip: AVR32, ARM7, ARM9, Cortex-M3/M4/M7, SAM3/4/7/9/A/C/D/E/G/L/SV, PIC24/PIC32

  • Microsemi: RISC-V

  • NXP: LPC, ARM7, ARM9, PowerPC, 68 K, i.MX, ColdFire, Kinetis Cortex-M3/M4

  • Renesas: SH, HS, V850, RX, RZ, Synergy

  • Silicon Labs: EFM32

  • Synopsys: ARC 600, 700, ARC EM, ARC HS

  • ST: STM32, ARM7, ARM9, Cortex-M3/M4/M7

  • Tl: C5xxx, C6xxx, Stellaris, Sitara, Tiva-C

  • Wave Computing: MIPS32 4K, 24 K, 34 K, 1004 K, MIPS64 5K, microAptiv, interAptiv, proAptiv, M-Class

  • Xilinx: MicroBlaze, PowerPC 405, ZYNQ, ZYNQ UltraSCALE

All timing and size figures listed are estimates and may be different on your development platform.

In the context of Azure IoT

In addition to directly connecting to Azure IoT or indirectly connecting through Azure IoT Edge, Azure RTOS is also available on Azure Sphere devices. The combination of Azure RTOS and Azure Sphere bring best-of-class real-time processing and security together in one device.