What are the five most commonly used real-time operating systems? [closed]

Question

I am looking for mostly used 5 Real-Time operating systems. I searched on Google and Wikipedia has a list of RTOSs, but they are in random order and also I am not convinced that all of them really operating real-time.

One more question: can we include Windows 7? When we set priority of 5 tasks, for example to realtime.

Answer 1

Real-time operating systems that I have come in contact with, in order of (subjective) impact:

• VxWorks
• QNX
• eCos
• RTLinux

Especially VxWorks has a long history in critical applications - for example, in cars and various NASA space platforms. It is however neither free nor open source software - I would probably prefer eCos or RTLinux in one of my own projects.

This Wikipedia article also has a section with what is supposedly a list of the most deployed RTOS, although its contents are not supported by any references.

That said, if you search around a bit you will find that the most deployed RTOS are usually found in proprietary embedded systems. Many of those actually push the definition of an Operating System quite a bit (e.g. the various exokernel designs out there).

Without more informaton on your use of this list, we cannot provide more information. If you intend to develop RT software, for example, there are far more factors to consider than the popularity of each RTOS. Cost, supported hardware, familiarity with the various interfaces, vendor support for specific applications, quality of the development tools etc. should all be taken into account...

Answer 2

Out of Wikipedia's long list, the names I recognized as "deployed" amongst people I know:

eCos, LynxOS, QNX, RTAI, RTLinux, Symbian OS, VxWorks, Windows CE, MontaVista Linux.

Of these, I'd guess this order: Symbian OS, Windows CE, QNX, MontaVista, RTLinux. But those are my guesses. :)

If you want to include Soft Real-Time systems, Windows 7 and stock Linux might qualify. Depends upon your needs.

Answer 3

VDC do an annual survey of the embedded system market which would no doubt answer your question; you have to pay for the full report, but you can get the executive brief for free if you register.

From other sources: In 2006 of the commercial RTOS vendors the following led:

• VxWorks
• XP Embedded
• Windows CE
• DSP/BIOS
• Red Hat Linux

Now, these are from survey responses, and some of these I would not consider Real-Time, so if you weed out the non-real-time OSs, I would say:

• VxWorks
• Windows CE
• DSP/BIOS
• QNX
• RTX

But survey response is not divided by platform type; what is appropriate to an 8 bit system, or a deeply embedded system with no need for file-systems, networking, or display etc. are very different. And if you have never used a TI DSP, you'd never have even encountered DSP/BIOS before. So the question itself is probably too simplistic to answer, since to get meaningful results you probably have to specify the target platform and application complexity.

The survey also does not consider non-commercial RTOS such as FreeRTOS, RTEMS, and eCOS. These are very worthy of consideration and in some cases of superior quality to some commercial systems. In 2009 for example FreeRTOS was downloaded more than 77500 times, and eCOS has extensive support for file-systems and networking etc. Of course no one can tell how many such RTOSes are used in real products or simply by hobbyists or even downloaded and never used.

Another question is whether you are interested in volume of product or number of distinct projects? For example WidgetA may incorporate say Keil RTX bundled free with its ARM-MDK, and sell in millions, while PABX-Exchange-B, may use VxWorks costing tens of thousands in royalties and development licences, but sell in the few tens. The comparison is pointless.