Overview of GCOS 64 Operating System architecture
SECTION 1
Architectural Concepts

SECTION 2
the GCOS computer model

SECTION 3
Structure of the Operating System.

SECTION 4
Modes and Emulators

SECTION 5
Interactive Modes of operation

SECTION 6
Miscellaneous
© Jean Bellec 2001

Thirty one years after having written, with Claude Carré, André Bensoussan and Axel Kvilekvaal a first draft about the "APL OS" architecture, and seven years after leaving Bull, I felt worthwhile to revisit the past in writing a description of what has been eventually that operating system.  The description is written here assuming that the reader has more knowledge of modern operating systems than familiarity with the pre-1970 state of the art.

Since 1974, we have been somewhat frustrated by the secrecy that had enveloped the inside of this project. Customers were given only a sketchy idea of their OS. University people and even French computer scientists consequently ignored the creation of the Bull engineers. Our nostalgia does not mean that we believe that the industry has missed a great opportunity to build on the base of GCOS rather to rely on more popular systems that have invaded our personal computers and servers. The architectural concepts of our system were designed when the modern computer usage starts to appear and well before hardware became cheaper by several orders of magnitude. While such consideration also applies to IBM mainframes and to UNIX, the fact that GCOS 64 was considered as a proprietary system owned by what was then "the other computer company" deprived it from the acknowledgement that Open Systems were able to provide to its competitors.

After understanding what is behind GCOS 64/ GCOS 7 concepts, it will be seen that GCOS incorporated many of the features of systems appeared long after its introduction. It will explain reasons for diverging from more celebrated OS and attempt to explain reasons behind the complexity of some mechanisms.

This paper does not describe the "history" of GCOS birth and its evolution described in other documents of this site.


GCOS here is used for GCOS 64 and GCOS 7, two successive names for essentially the same product. GCOS 7 design is completely different from GECOS III or GCOS 8 as well as from GCOS 4 or GCOS 6.