An experimental comparison of problem-solving using time-sharing and batch-processing computer systems conducted at MIT is described in this paper. This study is the first known attempt to evaluate two such systems for what may well be the predominant user population within the next decade—the professionals who, as nonprogrammers, are using the computer as an aid in decision-making and problem-solving rather than as a programming end in itself.
Statistically and logically significant results indicate equal cost for usage of the two computer systems; however, a much higher level of performance is attained by time-sharing users. There are indications that significantly lower costs would have resulted if the time-sharing users had stopped work when they reached a performance level equal to that of the batch users. The users' speed of problem-solving and their attitudes made time-sharing the more favorable system.
Software Engineering and Programming Languages
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A note on reliable full-duplex transmission over half-duplex links
A simple procedure for achieving reliable full-duplex transmission over half-duplex links is proposed. The scheme is compared with another of the same type, which has recently been described in the literature. Finally, some comments are made on another group of related transmission procedures which have been shown to be unreliable under some circumstances.
Clarification of Fortran standards—initial progress
In 1966, after four years of effort, FORTRAN became the first programming language standardized in the United States. Since that intital achievement, study and application of the standard specifications have revealed the need for maintenance of the standards. As the result of work intiated in 1967, as initial set of clarifying interpretations has been prepared. The nature of the maintenance, corrections to the standard specifications, and completed interpretations are reported.
An automatic grading scheme for simple programming exercises
A discussion is given of alterations that were made to a typical university operating system to record the results of programming exercises in three different languages, includeing assembly language. In this computer-controlled grading scheme provision is made for testing with programmer-supplied data and for final runs with system-supplied data. Exercises run under the scheme may be mixed with other programs, and no special recognition of exercises by the operators is necessary.
Analysis of boolean program models for time-shared, paged environments
Directed graphs or their associated matrices are frequently used to represent the logical structure of sequences of computer instructions. Such techniques are used and, in addition, data references are represented in a nondirected model. The complete structural specification of a program is represented by a combined model. A transformation of the combined model yields a new model in which additional timing information is also contained. Analysis of these models prior to execution yields information valuable in determining segmentation of instructions and data for a time-shared environment, as well as for initial page loading; during execution, the analysis may be used for “look ahead” control of page turning.
Organizing matrices and matrix operations for paged memory systems
Matrix representations and operations are examined for the purpose of minimizing the page faulting occurring in a paged memory system. It is shown that carefully designed matrix algorithms can lead to enormous savings in the number of page faults occurring when only a small part of the total matrix can be in main memory at one time. Examination of addition, multiplication, and inversion algorithms shows that a partitioned matrix representation (i.e. one submatrix or partition per page) in most cases induced fewer page faults than a row-by-row representation. The number of page-pulls required by these matrix manipulation algorithms is also studied as a function of the number of pages of main memory available to the algorithm.
Concepts of use in contour map processing
Generalized techniques are developed whose use can simplify the solution of problems relating to contour maps. One of these techniques makes use of the topological properties of contour maps. The topology is represented by a graphical structure in which adjacent contour lines appear as connected nodes. Another generalized technique consists of utilizing geometrical properties to determine the characteristics of straight lines drawn on the contour map. Both of these techniques have been applied to the problem of locating the ground track of an aircraft from elevation readings obtained during a flight.
Data communications control procedures for the USA standard code for information interchange
This proposed American Standard has been accepted for publication by USA Standards Committee X3, Computers and Information Processing. In order that the final version of the proposed standard reflect the largest public consensus, X3 authorized publication of this document to elicit comment and general public reaction, with the understanding that such a working document is an intermediate result in the standardization process and is subject to change, modification, or withdrawal in part or in whole. Comments should be addressed to the X3 Secretary, Business Equipment Manufacturers Association, 235 East 42 Street, New York, NY 10017.—E. L.
Coding the Lehmer pseudo-random number generator
An algorithm and coding technique is presented for quick evaluation of the Lehmer pseudo-random number generator modulo 2 ** 31 - 1, a prime Mersenne number which produces 2 ** 31 - 2 numbers, on a p-bit (greater than 31) computer. The computation method is extendible to limited problems in modular arithmetic. Prime factorization for 2 ** 61 - 2 and a primitive root for 2 ** 61 - 1, the next largest prime Mersenne number, are given for possible construction of a pseudo-random number generator of increased cycle length.
Extremely portable random number generator
Extremely portable subroutines are sometimes needed for which moderate quality and efficiency suffice. Typically, this occurs for library functions (like random number generation and incore sorting) which are not entirely universal or are not used in a standardized way.
The literature on random number generators does not seem to contain an algorithm that meets requirements of this sort. An extremely portable 8-line FORTRAN program is provided which is based on an important paper by Coveyou and MacPherson (1967). Using their methods, Fourier analysis is applied to the probability function for the consecutive n-tuples provided by our generator (with n less than or equal to 4). While the small modulus which must be used to maintain portability prevents the quality of the generator from being high, the generator compares well with the bounds established in the above mentioned paper.
Randomized binary search technique
A mathematical model is developed for the mean and variance of the number of trials to recover a given document in a randomly received list of files. The search method described is binary in nature and offers new potential for information retrieval systems.
Exclusive simulation of activity in digital networks
A technique for simulating the detailed logic networks of large and active digital systems is described. Essential objectives sought are improved ease and economy in model generation, economy in execution time and space, and a facility for handling simultaneous activities. The main results obtained are a clear and useful separation of structural and behavioral model description, a reduction of manual tasks in converting Boolean logic into a structural model, the elimination of manual processes in achieving exclusive simulation of activity, an event-scheduling technique which does not deteriorate in economy as the event queue grows in length, and a simulation procedure which deals effectively with any mixture of serial and simultaneous activities. The passage of time is simulated in a precise, quantitative fashion, and systems to be simulated may be combinations of synchronous and asynchronous logic. Certain aspects of the techniques described may be used for the simulation of network structures other than digital networks.
CODAS, a Customer Oriented Data System, is a user-oriented data retrieval and display system. The command language of the system provides the user with an easy means for specifying data retrieval and display requests. Data is displayed as tables and graphs produced in a format ready for publication. In this paper the statements of the request language and the general system design are described.
Some criteria for time-sharing system performance
Time-sharing systems, as defined in this article, are those multiaccess systems which permit a terminal user to utilize essentially the full resources of the system while sharing its time with other terminal users. It is each terminal user's ability to utilize the full resources of the system that makes quantitative evaluation of time-sharing systems particularly difficult. Six criteria are described which have been successfully used to perform first-level quantitative time-sharing system performance evaluation.
Directed random generation of sentences
The problem of producing sentences of a transformational grammar by using a random generator to create phrase structure trees for input to the lexical insertion and transformational phases is discussed. A purely random generator will produce base trees which will be blocked by the transformations, and which are frequently too long to be of practical interest. A solution is offered in the form of a computer program which allows the user to constrain and direct the generation by the simple but powerful device of restricted subtrees. The program is a directed random generator which accepts as input a subtree with restrictions and produces around it a tree which satisfies the restrictions and is ready for the next phase of the grammar. The underlying linguistic model is that of Noam Chomsky, as presented in Aspects of the Theory of Syntax. The program is written in FORTRAN IV for the IBM 360/67 and is part of a unified computer system for transformational grammar. It is currently being used with several partial grammars of English.
Methods of analyzing the control flow and data flow of programs during compilation are applied to transforming the program to improve object time efficiency. Dominance relationships, indicating which statements are necessarily executed before others, are used to do global common expression elimination and loop identification. Implementation of these and other optimizations in OS/360 FORTRAN H are described.
The role of programming in a Ph.D. computer science program
In this general paper the role of programming in advanced graduate training is discussed. Subject matter related to programming as well as programming per se is considered. The importance and application of formalism are considered and also the need for good empirical experimentation. A brief outline for a sequence of courses is included, and subject headings that have been obtained from an extensive bibliography are given. A bibliography of programming references is included.
A system organization for resource allocation
This paper introduces a system for resource management using the concepts of “process,” “facility,” and “event.” Except for the processor no attempt has been made to give serious suggestions for the policy to be followed for resource allocation. However, a basic framework is provided in which a system analyst can express solutions to resource management problems.
The paper is divided into a tutorial presentation, a description of the system primitives, and a small collection of examples of the use of the primitives.
A SIMSCRIPT-FORTRAN case study
Two programs for a vehicle dispatching model, one written in 7040 SIMSCRIPT and the other in 7040 FORTRAN IV are compared. The comparison is made in terms of basic program design decisions, storage requirements, computer time used, and the ease of making changes.
In the SIMSCRIPT program, the primary design considerations center around the choice of model variables, model changing events, and model testing. In the FORTRAN program, basic design problems relate to the representation of the passage of time, the allocation of storage, and the organization of input data.
The comparison of these differently designed programs shows that the SIMSCRIPT program uses more computer storage and more computer time, but requires fewer program changes to introduce model revisions.
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