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Norman R. Nielsen

Research and Advances Nov 1 1977

Dynamic memory allocation in computer simulation

e of 35 dynamic memory allocation algorithms when used to service simulation programs as represented by 18 test cases. Algorithm performance was measured in terms of processing time, memory usage, and external memory fragmentation. Algorithms maintaining separate free space lists for each size of memory block used tended to perform quite well compared with other algorithms. Simple algorithms operating on memory ordered lists (without any free list) performed surprisingly well. Algorithms employing power-of-two block sizes had favorable processing requirements but generally unfavorable memory usage. Algorithms employing LIFO, FIFO, or memory ordered free lists generally performed poorly compared with others.

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Author Archives

Research and Advances Feb 1 1971

An analysis of some time-sharing techniques

The effectiveness of certain time-sharing techniques such as program relocation, disk rotational delay minimization, and swap volume minimization is investigated. Summary data is presented, and the findings are discussed. The vehicle for this investigation was a SIMULA based simulation model reflecting an early framework for a planned Burroughs B6500 time-sharing system. Inasmuch as the B6500 system is based upon the use of variable sized segments and a dynamic overlay procedure, data is also presented which provides some indication of the effectiveness of this type of organization in a time-sharing environment. The design characteristics and operational capabilities of the simulation model are also described.
Research and Advances Aug 1 1970

The allocation of computer resources—is pricing the answer?

The widespread use of complex third generation computing systems has led to a much broader concern about the means by which the resources of these systems are allocated among the user community. One means that is suggested more and more frequently is a pricing procedure. In this paper the manner in which one would like to allocate computing resources is considered, and then the extent to which a pricing mechanism fits this mold is discussed. Inasmuch as pricing must serve as a rationing mechanism at times, consideration is given to the means by which prices can be adjusted flexibly in order to make a dynamic allocation of resources. Consideration is also given to the means by which users can be insulated from the harmful effects of frequent price fluctuations. Although the subject of pricing has been given a lot of attention recently, a number of misconceptions persist about its purpose and its operation. An attempt is made to clarify some of these misunderstandings and to highlight the advantages and disadvantages of pricing. Two illustrative pricing systems are also discussed in order to demonstrate the applicability of pricing in quite different environments.
Research and Advances Jul 1 1967

The simulation of time sharing systems

The development of new large scale time-sharing systems has raised a number of problems for computation center management. Not only is it necessary to develop an appropriate hardware configuration for these systems, but appropriate software adjustments must be made. Unfortunately, these systems often do not respond to changes in the manner that intuition would suggest, and there are few guides to assist in the analysis of performance characteristics. The development of a comprehensive simulation model to assist in the investigation of these questions is described in this paper. The resulting model has a general purpose design and can be used to study a variety of time-sharing systems. It can also be used to assist in the design and development of new time-sharing algorithms or techniques. For the sake of efficiency and greater applicability, the model was implemented in a limited FORTRAN subset that is compatible with most FORTRAN IV compilers. The use of the simulation is demonstrated by a study of the IBM 360/67 time-sharing system.
Artificial Intelligence and Machine Learning

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