General Comprehensive Operating System

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GCOS /jee'kohs/ (General Comprehensive Operating System) is a family of Operating Systems orientated toward mainframes. Its initial member was developed by General Electric from 1962; originally called GECOS (the General Electric Comprehensive Operating Supervisor).

It is still in use nowadays, although very rarely and often due to legacy reasons. Programs for this Operating System are usually written in GMAP (assembler), COBOL, Fortran, or ALGOL.

1 System Architecture and Concepts
2 History
3 Trivia
4 See also
5 External links

[edit] System Architecture and Concepts

GCOS uses the concept of process to describe sequence of instructions executed in a processor on a set of data. It has also the concept of multi-threading. Additionally, there exist what is called a process group which is an entity containing several processes loaded and scheduled simultaneously. GCOS provides also semaphores which can be used to synchronise processes with each other or with the hardware.

Each process has its own address space, on which access rights can be a mix of READ, WRITE, and EXECUTE. The address space is segmented, allowing to share some part of the data between processes. Privilege management is done via rings. Each process is associated to one ring, the lower it is, the more privileges the process has.

The operating system is able to handle SMP based computers. It is based on a microkernel implemented in the firmware of the machine. It has also the ability to run in emulating modes with very little in speed loss.

[edit] History

The GECOS-II operating system was developed by General Electric for the 36-bit GE-635 in 1962-1964. Contrary to rumor, GECOS was not cloned from System/360 (unfortunately the on-line "Jargon File" has perpetuated a rumor that this was a "quick and dirty clone of System/360 DOS") - the GE-635 architecture was very different from the IBM 360 and GECOS was more ambitious than DOS/360. One of the hallmarks of the true second generation of this OS was its support of Time-sharing ("TSS") along with batch.

After the buy-out of GE's computer division by Honeywell, GECOS-III was renamed GCOS-3, and the hardware line was renamed to the H-6000. Later Honeywell Marketing created a "Series" 60, and renamed the H-6000 to the Level-66. Honeywell, along with its European affiliate CII-Honeywell Bull, also decided to launch a new product line called Level 64 (this later became the DPS-7).

The name "GCOS" was extended to all Honeywell-marketed product lines and GCOS-64, a completely different 32-bit operating system, significanctly inspired by a parallel development called "Multics," was designed by Honeywell and Honeywell Bull developers in France and Boston. GCOS-62, another different 32-bit low-end OS was designed in Italy. GCOS-61 represented a new version of a small system made in France and the new DPS-6 16-bit minicomputer line from Massachusetts got the name GCOS-6.

Yet another renaming of the product lines occurred in 1979, with the Level-6 becoming the DPS-6, the Level-61 becoming the DPS-4, the Level-64 becoming DPS-7, and Level-66 becoming DPS-8. Operating Systems retained the GCOS brand-name, with GCOS 6, GCOS 4, GCOS 7, and GCOS 8 being introduced. This caused some confusion in the customer base, since the original GCOS line, called GCOS-III (or GCOS-3), was now suddenly GCOS 8. GCOS-3 was supported in maintenance for several years after this announcement and renaming.

GCOS-3 (and later GCOS-7 and GCOS-8) featured a good Codasyl database called IDS (Integrated Data Store) that was the model for the more successful IDMS.

Several transaction processing monitors were designed for GCOS-3 and GCOS-8. An early attempt at TP for GCOS-3 assumed that, as in Unix, a new process should be started to handle each transaction. IBM customers required a more efficient model where multiplexed threads wait for messages and can share resources. Those features were implemented as subsystems.

GCOS-3 soon acquired a proper TP monitor called Transaction Driven System (TDS). TDS was essentially a Honeywell development. It later evolved into TP8 on GCOS-8. TDS and its developments were commercially successful and predated IBM CICS, which had a very similar architecture. A similar product also called TDS was developed for GCOS-7.

GCOS-6 and GCOS-4 (ex-GCOS-62) were superseded by Motorola 68000-based and PowerPC minicomputers running Unix and the product lines were discontinued, though GCOS-6 ran in an emulator on top of AIX. The DPS-7 line, along with GCOS 7, continued to evolve into the DPS-7000 hardware base.

In the late 1980s Honeywell sold its computer business to a joint venture that initially included NEC and Bull, with Honeywell for a time still holding a stake. Over a couple of years, Bull took over the company. NEC supplied several generations of mainframe hardware at the high end, which would run both GCOS 8 and their own ACOS-4 Operating System. Bull used the nomenclature DPS-9000 for its entire GCOS 8-based mainframe line, which included models designed by both Bull and NEC.

By the late 1990s and early 2000s, Bull's desire was to center its development on a single hardware base, running commodity Intel chips but with Bull value-adds. This platform, called Novascale and based on Itanium 2 processors, runs both Windows and Linux natively. However, Instruction Set Simulators for both the DPS-7000 and DPS-9000 allowed GCOS 7 and GCOS 8 to run on this platform. Bull continues to invest development money in support of both GCOS 7 and GCOS 8, and still has customers in several countries around the world.

[edit] Trivia

Some early Unix systems at Bell Labs used GCOS machines for print spooling and various other services. The field added to "/etc/passwd" to carry GCOS ID information was called the "GECOS field" and survives today as the "pw_gecos" member used for the user's full name and other human-ID information.