Chorus Systèmes

» see chorus.com as it lived, on the wayback machine

~ the eulogy ~

The Chorus project began at INRIA in 1979, which is seven years before anyone tried to sell it. It was started by Hubert Zimmermann, who had come out of the French CYCLADES networking work and had devised the OSI reference model, the seven-layer diagram that ended up on the wall of every networking course in the world. The idea he carried into operating systems was the one he already had about networks: that the inside of a computer was also a communication problem, and a kernel could be built as a set of things passing messages rather than as one large program.

Several versions were built at INRIA between 1980 and 1986. A second project there, Michel Gien's Sol, was writing a Unix in Pascal for French minicomputers, and in 1984 the two merged, which is why Chorus stopped having its own interfaces and adopted those of Unix System V. In 1986 Zimmermann and Gien founded Chorus Systèmes SA at Saint-Quentin-en-Yvelines to sell the result. French technology startups were rare enough at the time that the trade press wrote profiles about the fact of the company existing at all.

For the next eleven years Chorus was never quite the product. It was the layer other companies planned to build their product on. Novell was going to use it for SuperNOS. SCO was going to use it for a telecommunications version of OpenServer. Both of those plans died inside the companies that made them, and Chorus Systèmes kept selling the kernel to the people who actually shipped: by 1997 its customers were Alcatel-Alsthom, Lucent, Matra and Motorola, and its revenue was $10 million a year.

Sun Microsystems announced it was buying the company on 10 September 1997 and closed the deal on 21 October for the equivalent of $26.5 million. Chorus went into a new Embedded Systems Software group alongside Sun's JavaOS team, and the name became ChorusOS. Computergram's view at the time was that with interest in microkernels already falling away, Chorus Systèmes was lucky to have found a buyer at all.

~ the dossier ~

~ what a microkernel promised ~

In the late 1980s this was the obvious future. Take the operating system apart, leave a tiny core that does nothing but memory and messages, and run everything else, file systems and drivers and the Unix personality itself, as ordinary programs on top. You get fault isolation, and you get distribution across machines almost for free, because a message does not care which box it crosses. What Chorus liked to show off was the consequence: two operating systems running side by side on one machine, neither of them aware of the other.

Chorus went small as well as large. Under the European ESPRIT program it was restructured into a scaled family, the smallest member being a nanokernel of about ten kilobytes. The team also ported it to a Macintosh IIcx so that Chorus could be started from inside Mac OS and appear as an application within it, which they described as cohabitation. The object-oriented layer, COOL, was built with INRIA and SEPT, a France Telecom research lab, and was written up in Communications of the ACM in 1993.

~ the SuperNOS years ~

In 1994 Novell began describing SuperNOS in public: NetWare's network services and UnixWare's application services running together on a microkernel, the product that was finally going to deal with Windows NT. It was built on work already underway between Chorus and Unix System Laboratories, and it drew both attention and engineers. Then it spent its life in architectural argument, with Gien and Novell's chief scientist disagreeing in the trade press about whether the Chorus technology was up to the job. In 1995 Novell sold Unix to SCO and SuperNOS stopped existing.

SCO was running its own Chorus project in parallel, going back to a 1992 agreement about real-time telecom work. Chorus/Fusion shipped in 1994, a whole SCO business unit was reimplementing OpenServer on the Chorus microkernel by 1995, and in 1996 the two companies published a roadmap for a telephone-switch platform codenamed MK2 with Siemens Private Communications Systems named as an adopter. It was scrapped before it shipped. Two of the largest Unix companies of the decade each spent years betting on this kernel and neither of them ever put a product on a shelf.

~ where the code went ~

Sun kept ChorusOS through the end of the 1990s, pairing it with Solaris for high-availability telecom systems, and then dropped it during the restructuring of the early 2000s. About three dozen of the Sun engineers who had been working on it left and founded Jaluna, which took the same approach into virtualization, renamed itself VirtualLogix, and was bought by Red Bend Software in 2010. Neither Sun nor Oracle supports ChorusOS now.

Zimmermann's other object did better. I learned the seven-layer model in a classroom in Ankara, drew it in exams, and like everyone else never once thought about who had made it. The diagram outlived the operating system by a wide margin, and the company that was supposed to be the commercial half of that career is the part nobody remembers. chorus.com today belongs to an American firm selling what it calls AI employees.

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