The shortfall in the ability to produce credible real-time systems and software has become critical. The number of major civilian and military systems that have suffered expensive delays, failures, and functionality shortcomings is already large, and it is growing. Without a dramatically better scientific basis for designing and constructing real-time systems, massive expense will be incurred to build ill-functioning real-time systems. It is argued that there is an absolute need to invest in basic research on proof techniques, program semantics, scheduling theory, dependability, state-space modeling, and other approaches that offer the promise of being able to create a scientific basis for real-time system specification and construction. Currently known techniques appear to be incapable of dealing effectively with the state-space explosion problem. New basic insights and breakthroughs are essential.>

Guardian is a real-time, multimicroprocessor operating system intended to be a research testbed for experimentation with decentralized control. It was designed in a Pascal-like language for a target multimicroprocessor that contains six microcomputer processing elements and twelve shared memories fully interconnected by a crossbar switch. Each processing element in the host multimicroprocessor executes Gaurdian tasks that perform shared memory reclamation, internodal communication, health monitoring, task scheduling, fault containment, and distributed debugging. Each node also supports application-callable software primitives for realtime process control, message-based interprocess communication, shared data structure management, and exception handling. The primary goal of Guardian is to demonstrate hard real-time decentralized control of an embedded multimicroprocessor.

Decentralized operating systems that control large multicomputers need techniques to schedule competing parallel programs called task forces. Wave scheduling is a probabilistic technique that uses a hierarchical distributed virtual machine to schedule task forces by recursively subdividing and issuing wavefront-like commands to processing elements capable of executing individual tasks. Wave scheduling is highly resistant to processing element failures because it uses many distributed schedulers that dynamically assign scheduling responsibilities among themselves. The scheduling technique is trivially extensible as more processing elements join the host multicomputer. A simple model of scheduling cost is used by every scheduler node to distribute scheduling activity and minimize wasted processing capacity by using perceived workload to vary decentralized scheduling rules. At low to moderate levels of network activity, wave scheduling is only slightly less efficient than a central scheduler in its ability to direct processing elements to accomplish useful work.

Abstract This article describes a simple graphics compiler which allows the owner of a personal computer system with a graphics display and access to a larger computer to execute large application programs remotely but still use his display as though the programs were running locally. Simple graphics primitives and the program structures used to implement them are discussed. The compiler includes a simple packet switching subsystem which allows display data to be transmitted over the telephone network.

Packet switching is a communication technology which has been used extensively in geographically distributed computer networks. It is also applicable to the communication subnetworks of compact multimicrocomputers known as network computers. This paper describes the use of the language Concurrent Pascal to build a packet-switching subsystem for the MICRONET network of DEC LSI-11 microcomputers. Examples of actual Concurrent Pascal source code taken from the system demonstrate the usefulness of high-level languages with abstract data types for complex communication software.

MICROS is the distributed operating system for the MICRONET network computer. MICRONET is a reconfigurable and extensible network of 16 loosely coupled LSI-11 microcomputer nodes, connected by packet-switching interfaces to pairs of high-speed shared communication buses. MICROS simultaneously supports many users, each running multicomputer parallel programs. MICROS is intended for control of network computers of thousands of nodes.