Author Archives

Research and Advances

The selection of optimal tab settings

A new generation of computer terminals allows tab settings to be selected and set by the computer. This feature can be used to reduce the number of characters that are needed to represent a document for transmission and printing. In this note, an algorithm is given for selecting the optimal set of tab stops for minimizing the number of characters transmitted. An implementation of the algorithm has reduced the number of characters transmitted by from 7 to 30 percent, but requires a prepass through the document to compute a matrix used in determining the optimal set of tab stops. The use of fixed tab stops, as a heuristic alternative, can achieve about 80 percent of optimal with no prepass.
Research and Advances

Proving monitors

Interesting scheduling and sequential properties of monitors can be proved by using state variables which record the monitors' history and by defining extended proof rules for their wait and signal operations. These two techniques are defined, discussed, and applied to examples to prove properties such as freedom from indefinitely repeated overtaking or unnecessary waiting, upper bounds on queue lengths, and historical behavior.
Research and Advances

Mixed solutions for the deadlock problem

Mixtures of detection, avoidance, and prevention provide more effective and practical solutions to the deadlock problem than any one of these alone. The individual techniques can be tailored for subproblems of resource allocation and still operate together to prevent deadlocks. This paper presents a method, based on the concept of the hierarchical operating system, for constructing appropriate mixtures and suggests appropriate subsystems for the most frequently occurring resource allocation problems

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