Convergent Technologies Operating System

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

CTOS had many innovative features for its time. System access was controlled with a user password and Volume or disk passwords. 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. {Network Node}[VolumeName]<DirectoryName>FileName.

It was possible to custom-link the operating system to add or delete features.

CTOS supported a transparent peer-to-peer network carried over serial RS-422 cables (daisy-chain topology) and in later versions carried over twisted pair (star topology) with RS-422 adapters. Each workgroup (called a "cluster") was connected 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.

The Inter-process communication (IPC) is primarily based on the "request" and "respond" messaging foundation that enhanced the Enterprise Application Integration among services for both internal and external environments. Thus CTOS was well known for the message-based Micro-Kernel Architecture. Applications are added as services to the main server. Each client consumes the services via its own mailbox called "exchange" and well-published message formats. The communication works on "request codes" that are owned by the service. The operating system maintains the exchanges, message queues, scheduling, control, message passing, etc., while the service manages the messages at its own exchange using "wait", "check", and "respond" macros.

CTOS ran on Intel x86 computers, and could run concurrently with Windows NT on Unisys PC.

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 an always-resident debugger.

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