PC fault-tolerant Unix-based system runs on a modular microkernel architecture

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Author: Sherry Van Tyle
Date: Oct. 15, 1992
From: Electronic Design(Vol. 40, Issue 21)
Publisher: Endeavor Business Media
Document Type: Article
Length: 814 words

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Tolerance Computer and Chorus systemes SA are working together to develop the first Unix system that is fault-tolerant running on a microcomputer. Tolerance's direct-connect architecture (DCA)-based boards are used with Chorus' microkernal architecture, Chorus/MiX. Tolerance's DCA boards link two standard 80486 and 80386-based microcomputers, both which run TCX, a fault-tolerant Unix operating system that is based on Chorus/MiX. The innovative fault-tolerant system is at the center of the $14 million Ouverture project that is included in the EEC's European Strategic Program for Research Information Technology.

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The first fault-tolerant Unix system to run on a PC teams up Chorus systemes' microkernel architecture and Tolerance Computer's direct-connect-architecture (DCA) boards. The Twinix approach from Tolerance, based in France, is built on two DCA boards that connect two standard PC 386/486 PCs bus-to-bus at 350 Mbits/s. Each PC runs TCX, a fault-tolerant Unix operating system (OS) based on Chorus/MiX, which is the distributed OS based on Chorus' microkernel architecture. Having the Unix OS run on PC-based products brings the power of low-cost fault tolerance to many applications that previously could not afford this feature.

With the microkernel approach, Chorus systemes SA of France, along with its Beaverton, Ore., U.S. subsidiary, has broken down the OS into modules. At the core of the OS is a message-based nucleus that controls communications within the OS. On top of the kernel rest the subsystems, which separate the functions of the OS into services to be supplied by independent servers.

In the past, the OS kernel contained these functions, making the OS monolithic and, as a result, more difficult to build on. Using the microkernel approach, subsystem servers not only have standards OS interfaces to application programs, but manage physical and local resources, such as files devices, and high-level communication services. The modules communicate by means of the nucleus's interprocess communication (IPC) manager.

Because subsystems rest on top of the enucleus, system builders can add a number of subsystems to extend system and OS capability. Most of the OS functions run outside the microkernel, therefore system builders can more easily incorporate such functions as fault-tolerance and security features, once found only on proprietary systems. For example, Chorus / MiX integrates the major functions of Unix System Laboratories original SVR4 kernel into servers that run on top of Chorus' distributed microkernel. As a result, developers can builds SVR4 systems for multicomputer architectures and real-time applications that are compatible with the SVR4 Application Binary Interface, Posix, as well as X/Open X Portability Guide Issue 3.

The nucleus of the microkernel contains an IPC manager. The IPC delivers messages throughout the system and can rely on external system servers to operate various network protocols. The nucleus also supplies a real-time multitasking executive that controls allocation of local processors and manages priority-based preemptive scheduling. A memory manager supports linear, segmented, or virtual memory. A low-level hardware supervisor enables device drivers or real-time event handlers to be loaded dynamically as separate system programs.

Basing the OS kernel on message-passing functions dates back to a networking project in the early 1970s at INRIA, the French national research institute for einformation sciences and automation. The project's goal was to integrate communications within an operating system. Ultimately, it played a key role in defining the Open Systems Interconnection standards and Transpac specifications for packet-switched networking. However, at the end of the project, a team of researchers led by Hubert Zimmermann went even further: They undertook the Chorus program to develop a distributed operating system suitable for a communucation environment. The idea was to develop a modular OS affording communication and message transfer among various sustems as if everything resided on the same machine.

By 1986, several prototypes had been developed, and the group wound up choosing Unix as the commercial vehicle for the communication functions. By the end of the year, Zimmermann, Michel Gien, and Marc Fuillemont founded Chorus systemes; a U.S. subsidiary followed in 1990.

Chorus technology borrows message-passing from the V kernel project of Stanford University, Palo Alto, Calif.; its distributed virtual memory and threads from the Mach project at Carnegie-Mellon University, Pittsburgh, Pa.; and its network addressing capabilities incorporates ideas from the e Amoeba project developed at the Vrije University and the Center for Mathematics and Computere Science, both in Amsterdam, the Netherlands.

The Chorus microkernel is at the center of the $14 million Ouverture project, which is part of the Espirit program run by the Commission of European Communities. With the goal of an open OS, Ouverture will integrate Chorus / MiX with Unix Syatem V release 4. Beyond the Unix market, the eproject will focus on real-time embedded systems and high-performance parallel-processing systems as part of the Open Microprocessor Systems Initiative and the High-performance Computing area under Esprit III. Among the companies contributing funds to the Ouverture project are Alcatel Alstrom, Olivetti, Siemens Nixdorf, and SGS-Thomson.

For additional information, contact Chorus Systems at (503) 690-2300.

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Gale Document Number: GALE|A14402019