Laszlo A. Belady

A study of replacement algorithms for a virtual-storage computer

One of the basic limitations of a digital computer is the size of its available memory. 1 In most cases, it is neither feasible nor economical for a user to insist that every problem program fit into memory. The number of words of information in a program often exceeds the number of cells (i.e., word locations) in memory. The only way to solve this problem is to assign more than one program word to a cell. Since a cell can hold only one word at a time, extra words assigned to the cell must be held in external storage. Conventionally, overlay techniques are employed to exchange memory words and external-storage words whenever needed; this, of course, places an additional planning and coding burden on the programmer. For several reasons, it would be advantageous to rid the programmer of this function by providing him with a “virtual” memory larger than his program. An approach that permits him to use a sufficiently large address range can accomplish this objective, assuming that means are provided for automatic execution of the memory-overlay functions.

A model of large program development

Discussed are observations made on the development of OS/360 and its subsequent enhancements and releases. Some modeling approaches to organizing these observations are also presented.

Dynamic space-sharing in computer systems

A formalization of relationships between space-sharing, program behavior, and processor efficiency in computer systems is presented. Concepts of value and cost of space allocation per task are defined and then value and cost are combined to develop a single parameter termed value per unit cost. The intent is to illustrate a possible analytic approach to the investigation of the problems of space-sharing and to demonstrate the method on sample problems.

System partitioning and its measure

Program modules and data structures are interconnected by calls and references in software systems. Partitioning these entities into clusters reduces complexity. For very large systems manual clustering is impractical. A method to perform automatic clustering is described and a metric to quantify the complexity of the resulting partition is developed.

An anomaly in space-time characteristics of certain programs running in a paging machine

The running time of programs in a paging machine generally increases as the store in which programs are constrained to run decreases. Experiment, however, have revealed cases in which the reverse is true: a decrease in the size of the store is accompanied by a decrease in running time. An informal discussion of the anomalous behavior is given, and for the case of the FIFO replacement algorithm a formal treatment is presented.

AN INTRODUCTION TO GROWTH DYNAMICS

Publisher Summary The behavior of smoothed data suggests that there is a self-regulating dynamics that underlies the growth of the system. That is, a system should be considered that comprises the body of code—constituting the programming system—together with the programmers that implement change and enhancement, their managers and executives, and the user population. The dynamics of this system, that is, the code, the programmer population, the applications, and the hardware, is governed by laws that cause it to be self-regulatory when its internal state changes with time. This chapter presents two models of this system, the macro-model and the micro-model.

GREENPRINT: a graphic representation of structured programs

To improve the readability of programs over existing techniques, a new program representation termed GREENPRINT has been developed and is discussed in this paper. GREENPRINTs (the name taken from the phosphor fluorescence of certain display terminals and paralleling the term blueprints) are tree-structured diagrams together with source code statements that represent the control structure of programs. Discussed in this paper are the diagramming conventions, control flow methodology, presentation graphics, and practical experience with GREENPRINTs.

The IBM history of memory management technology

The history of memory management technology in IBM during the period between the 1950s and the early 70s is discussed in this paper. The paper concentrates on the programming and operating system aspects of the problem, rather than the hardware technology involved.

The evolution of technology transfer at MCC's Software Technology Program: from didactic to dialectic

MCCs software technology program (STP) has a dual mission: to create tools and methodologies to assist development teams in the design of large, complex, distributed software systems, and to ensure the widespread diffusion of these technologies within STP shareholder organizations. STP has developed a comprehensive set of traditional technology transfer methods; although these methods make it possible to communicate research results successfully to shareholder receptors, they have spurred little actual use of released technology. STP has recently reevaluated its approach to technology transfer and discovered how it can be better accomplished-by fostering collaboration as its chief agent, rather than by depending on traditional transfer-and-feedback mechanisms. The authors describe the evolution of this new approach and present some of the results of collaborative experiences to date. It is found that collaborations revitalize research and that they empower STPs shareholders to affect the directions of that research.<<ETX>>

A computer graphics system for block diagram problems

An experimental on-line network design system is proposed. Called DESIGNPAD, it consists of a small computer with graphic display equipment connected to a time-sharing computer and includes the necessary programming support for the equipment. The system is designed to accept problems covering a broad spectrum of applications in the form of labeled block diagrams. The input/output medium, the man-machine interface, and the supporting data structures, particularly the cellular structure, are discussed.