Convergent Technologies Operating System

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The Convergent Technologies Operating System, also known variously as CTOS, BTOS and STARSYS, was a modular, message-passing, multi-process based operating system.

CTOS had many innovative features for its time.

The file system was hierarchical and allowed very long file names. Security was also hierarchical. If one knew the password, for example, for a volume, one could access any file or directory on that volume (hard disk.) Each volume and directory were referenced with delimiters to identify them, and could be followed with a file name, depending on the operation, i.e. [VolumeName]<DirectoryName>FileName.

The word processor was one of the first screen-oriented editors with many high-powered features, such as multiple views of the same file, cut/copy/paste, unlimited undo/redo, no typing lost after a crash, user-selectable fonts, and much more.

Most of the system programs were written in PL/M, an Algol-like language from Intel which compiled directly to object code without a runtime library.

The system API was presented to both high-level languages and assembly language. The assembler was very advanced, with a Lisp-like pattern-matching macro facility unmatched by almost any other assembler before or since.

There was a always-resident debugger.

The system shell was extensible — you could define new commands. Each command could request you fill out a form specifying the parameters it needed.

There was a "rats" game, using the programmable font generator to do simple graphics.

There was a transparent peer-to-peer network running over serial RS-422 cables, and later over twisted pair with RS-422 adapters. Each workgroup, called a "cluster," was connected via a daisy-chain topology to a server, called a "master." The workstations, normally diskless, were booted over the cluster network from the master, and could optionally be locally booted from attached hard drives.

You could custom-link the operating system to add or delete features.

Convergent Technologies' first product was the IWS (Integrated Workstation) based on the Intel 8086 processor, which had CTOS as its operating system. This was a modular operating system with built in local area networking. CTOS supports multiple processes or threads, and message-based inter-process communication.

Companies which licensed CTOS included Burroughs (BTOS) and Bull (STARSYS). The single largest customer was Unisys, with whom Convergent Technologies merged to become one company in 1988. At its peak, CTOS had over 800,000 users worldwide.

CTOS ran on Intel X86 computers, and could run concurrently with Windows NT. A typical B25 system looks like the following:

CTOS is no longer marketed to new customers; former major customers included police forces, banks, airlines, the U.S. Postal Service, the Drug Enforcement Administration, the U.S. Army and the U.S. Coast Guard. The Coast Guard used the operating system from approximately 1986 until 2000.

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.