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A promising DOS (windows) replacement. Worth watching, but written in hard to maintain, hard to adapt, even harder to read assembler. When will they ever learn?

Realtime OS 
guaranteed, ultra-fast interrupt response times -- features known as determinism and low latency -- required for heavy-duty, hard real-time applications: management and monitoring, programmable logic controllers, sensors and high-precision robotics, anti-lock-braking systems, test and instrumentation, printers and networking. 

The name Real-Time-Os should be reserved for systems with a dedicated real-time interrupt handler sheme. In reality it is not. Many systems call themselves real-time-systems without this prerequisite.

Why the concern about Microsoft's dominance of the PC's operating system?
The future belongs to embedded systems, which rely on real-time operating
systems (RTOSs).  Warren Webb instructs on the finer points of RTOSs: Some
stress speed, for example, while others stress modularity. To help you
through the RTOS maze, Warren lists an impressive array of RTOSs and
outlines their functions, features, and prices.

- Microtec Research, VRTX 
- Integrated Systems, pSOS 
- QNX from QNX Software Systems 
- VxWorks from Wind River Systems. 
- Windows CE 3.0 (1999) 
- QLX (?): Real-time-Unix. 

- ISI's pSOSystem, the industry's leading RTOS with over 4500 design wins, provides a complete RTOS support solution. 



Rhapsody (Apple Computer Corporation)
Related to: MacOS
Rhapsody is the code name for a new operating system from Apple Computer, Inc., designed to complement Mac OS by providing a variety of high-end solutions. The Rhapsody operating system, available on both PowerPC and Pentium-class processors, provides preemptive multitasking, protected memory, and other modern operating system features.


In traditional operating systems, input/output (I/O) subsystems implement a push-pull environment that provides system calls to allow user applications to pull data from or push data to a device. An important set of applications make combined use of push-pull to implement simple streaming, i. e. data is moved from one device to another with no transformations. Using push-pull I/O to implement these applications does not provide maximum performance. This work proposes a kernel design optimized for simple streaming applications. The Roadrunner operating system is being developed specifically to implement multiple, concurrent, high-speed speed data streams with Quality-of-Service (QOS) parameters.



REACTOS  (most active free NT alternative at the moment)

"ReactOS is a free and open-source operating system based on the Windows NT architecture, providing support for existing applications and drivers, and an alternative to the current dominant consumer and server operating systems.

Why re-implement NT?

First of all, the 'Windows' the general public knows is actually just one part of the modern Windows NT operating system. They usually mean the Win32 subsystem, a layer that sits upon the NT kernel, providing the user and application interface.

Most people think of 'NT' as 'WinNT 4', while in reality the term NT refers to the NT series, which ranges from version 3 over NT5 (2000, XP, 2003) to NT6 (Vista, 2008 and 7).
The NTarchitecture was designed by a team lead by David Cutler, a former lead developer of VMS. It took them more than 4 years to combine the best of UNIX, VMS and OS/2 and create the NT architecture.

In contrast to UNIX, ReactOS was designed for people familiar and comfortable with the Windows environment. Everything can be done through the well known Win32 user interface and advanced users are free to automate tasks with scripts or use the console.
Compatible"Change your OS, not your software!"

The ReactOS project reimplements a state-of-the-art and open NT-like operating system based on the NT architecture. It comes with a WIN32 subsystem, NT driver compatibility and a handful of useful applications and tools.

ReactOS combines the power and strengths of the NT kernel - which is well known for its extensibility, portability, reliability, robustness, performance and compatibility with Win32 compatibility. In short, ReactOS is designed to be powerful and lightweight. You can think of the term "lightweight" in the good old fashion of Win95, a consistent user interface and small bundle of very common and useful tools. Although lightweight, ReactOS offers a lot in comparison to Windows 95, with an up-to-date experience as well as built from scratch on a rock solid NT core.
ReactOS is free software, the source code of the whole system is available for free and it is licensed under the GNU GPL license. "'Free' as in 'free speech' and as in 'free beer'"

ReactOS does not phone home or track your usage, nor does it contain spy-software. As a matter of fact, other well known competitors are known for such practices.

Life with other operating systems tends to be a love-hate relationship, with most people falling strongly on one side or the other. The ReactOS project has a great community that is well appreciated." REACTOS Homepage

Take part in the developpment of reactos

Support REACTOS: developpers, testers, writers.... needed!



Real-Time Mach Project (Carnegie Mellon University)
Related to: Mach
Real-Time Mach is a research prototype real-time operating system intended for use as a vehicle for doing real-time systems research. The system is being developed by the ART Project in the School of Computer Science, Carnegie Mellon University.




RTS-80 was introduced in the beginning of the eighties. It was a real-time messages/semaphore-based Multitask/Multiuser-System on the basis of the Z80 and was CP/M compatible - the most used system in the 70th/80th. A huge software basis was thus available for this system. Preemptive multitasking and run-time linking (DLL's !) were features of RTS-80 from its very start, features which Windows learnt only 10-15 years later. RTS-80 had a command set comparable to UNIX, knew pipes and all sort of redirections Unix was able to do. With the aid of a memory management unit RTS-80 was able to address 1Mbyte of memory, an unbelievable huge memory at that time ( the 1983 available IBM-PC could address maximaly 640kbyte, normally it was delivered with 64kbyte). The system featured a driver based IO-system with semaphore locking, making extensions easy. RTS-80 could address harddisks up to 1GB, a hugeness only reached in the 90th. At that time harddiscs of 10-30Mbyte were usual (prices around 10.000$ !!). One of the biggest advantages and at the same time the biggest drawback of RTS-80 was that it was completely written in Assembler, making it a very fast OS. On the other hand this made porting to the emerging 16/32-bit processors a hard to accomplish task. In the mid-eighties a version for the National 16032/32032 was introduced, but since National was unable to sell these really fine processors, RTS-80/32 found no market(see MicroProcessor). Eventually National stopped production of these really fine processors (beginning 90ths) which rivaled the much later introduced 80486 in computing power.

The multitask-kernel of RTS-80 (without filesystem, today we would call this a micro-kernel) was distributed separately in source code. The kernel had due to an elaborate design a very short reaction time in task switching. A sophisticated interrupt handler sheme guaranteed fastest response times. Non-blocking techniques were used throughout. This was one of the reasons why many robots in the automobile industry were based on this multitask-kernel. RTS-80 is the seldom case where a book of the author accompanied the system, describing all essential internal workings. It appeared in the late 80th :"R.Bitsch:Multitask,multiuser,multi-processor-systems",Frankfurt/Thun. It is now out of print and no more deliverable.


Redstone Military Arsenal)
RTEMS is a real-time operating system for embedded computer systems with the following features:

  • support for homogeneous and heterogeneous multiprocessor systems
  • event-driven, priority-based, preemptive scheduling
  • optional rate monotonic scheduling
  • intertask communication and synchronization
  • responsive interrupt management
  • dynamic memory allocation


Group Members: RTMX Incorporated
RTMX is a commercial, BSD 4.4-derived, real-time system that offers POSIX 1003.4 real-time programming support with user tunability along with the standard UNIX functionality of BSD networking, X windows, and a full C development environment.



RTX is a very small, very fast real time executive that utilizes signals and queuing as a basis for managing and scheduling tasks. It becomes very easy to support multiple processors, communication channels, and to synchronize processes. RTX is completely free, but it is not public-domain software. If you decide to use the software, you may receive an automatic license to do so even in commercial products, if you provide adequate, reasonable credit to its developer.



One of the many assembler Dos-clones.


All about OSs



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