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Research and Advances Sep 1 1978

A note on virtual memory indexes

In [4] Maruyama and Smith analyzed design alternatives for virtual memory indexes. The indexes investigated were those modeled on the structure of VSAM [5] which are closely related to B-trees [1]. Maruyama and Smith presented alternatives for search strategies, page format, and whether or not to compress keys. They made a comparative analysis based on the average cost of processing the index for retrieval of a key with its associated data pointer (or a sequence of keys and data pointers). The analysis showed that the optimal solution depends on machine and file characteristics and they provided formulas for selecting the best alternative. In this brief note1 we propose that another alternative for the page format be considered. The basic idea is to replace the sequential representation within a page by a linked representation. The main advantage of this method is realized in the construction (and maintenance) phase of the index. Although this phase is difficult to analyze quantitatively—as alluded to in [4]—we provide data to substantiate our claim of a net saving in construction cost without any corresponding loss in the average retrieval cost. In the ensuing discussion we assume that the reader is familiar both with B-trees and the paper of Maruyama and Smith [4].
Research and Advances Sep 1 1978

A model for verification of data security in operating systems

Program verification applied to kernel architectures forms a promising method for providing uncircumventably secure, shared computer systems. A precise definition of data security is developed here in terms of a general model for operating systems. This model is suitable as a basis for verifying many of those properties of an operating system which are necessary to assure reliable enforcement of security. The application of this approach to the UCLA secure operating system is also discussed.
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Research and Advances Sep 1 1978

A controlled experiment in program testing and code walkthroughs/inspections

This paper describes an experiment in program testing, employing 59 highly experienced data processing professionals using seven methods to test a small PL/I program. The results show that the popular code walkthrough/inspection method was as effective as other computer-based methods in finding errors and that the most effective methods (in terms of errors found and cost) employed pairs of subjects who tested the program independently and then pooled their findings. The study also shows that there is a tremendous amount of variability among subjects and that the ability to detect certain types of errors varies from method to method.
Research and Advances Aug 1 1978

Value conflicts and social choice in electronic funds transfer system developments

During the last few years, computer-based systems which automate the transfer and recording of debits and credits have begun to be implemented on a large scale. These systems promise both financial benefits for the institutions that use them and potential conveniences to their customers. However, they also raise significant social, legal, and technical questions that must be resolved if full scale systems for Electronic Funds Transfer (EFT) are not to cause more problems for the larger public than they solve. This paper examines the incentives for EFT developments and the social problems they raise in the context of conflicts between five different value positions that are often implicit in analyses of proposed EFT arrangements. These conflicts reflect the relative importance of certain problems for specific groups. The value positions implicit in EFT proposals help to organize analyses of market arrangements, system reliability, and privacy of transactions. These topics are analyzed in this article and related to the value positions held by concerned parties. Last, the ways in which the public can learn about the social qualities of different EFT arrangements and the pace of EFT developments are both discussed in the context of social choice.
Research and Advances Jun 1 1978

Characteristics of application software maintenance

Maintenance and enhancement of application software consume a major portion of the total life cycle cost of a system. Rough estimates of the total systems and programming resources consumed range as high as 75-80 percent in each category. However, the area has been given little attention in the literature. To analyze the problems in this area a questionnaire was developed and pretested. It was then submitted to 120 organizations. Respondents totaled 69. Responses were analyzed with the SPSS statistical package. The results of the analysis indicate that: (1) maintenance and enhancement do consume much of the total resources of systems and programming groups; (2) maintenance and enhancement tend to be viewed by management as at least somewhat more important than new application software development; (3) in maintenance and enhancement, problems of a management orientation tend to be more significant than those of a technical orientation; and (4) user demands for enhancements and extension constitute the most important management problem area.
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Research and Advances Jun 1 1978

Some basic determinants of computer programming productivity

The purpose of this research was to examine the relationship between processing characteristics of programs and experience characteristics of programmers and program development time. The ultimate objective was to develop a technique for predicting the amount of time necessary to create a computer program. The fifteen program characteristics hypothesized as being associated with an increase in programming time required are objectively measurable from preprogramming specifications. The five programmer characteristics are experience-related and are also measurable before a programming task is begun. Nine program characteristics emerged as major influences on program development time, each associated with increased program development time. All five programmer characteristics were found to be related to reduced program development time. A multiple regression equation which contained one programmer characteristic and four program characteristics gave evidence of good predictive power for forecasting program development time.
Research and Advances Jun 1 1978

Automated welfare client-tracking and service integration: the political economy of computing

The impacts of an automated client-tracking system on the clients, caseworkers, administrators, and operations of the welfare agencies that use it are reported. The major impact of this system was to enhance the administrative attractiveness of the using agencies in the eyes of funders rather than to increase their internal administrative efficiency. This impact is a joint product of both the technical features of the computer-based system and of the organizational demands placed upon different agencies, administrators, and caseworkers. It illustrates the way “successful” automated information systems fit the political economies of the groups that use them.
Research and Advances Apr 1 1978

Secure communications over insecure channels

According to traditional conceptions of cryptographic security, it is necessary to transmit a key, by secret means, before encrypted massages can be sent securely. This paper shows that it is possible to select a key over open communications channels in such a fashion that communications security can be maintained. A method is described which forces any enemy to expend an amount of work which increases as the square of the work required of the two communicants to select the key. The method provides a logically new kind of protection against the passive eavesdropper. It suggests that further research on this topic will be highly rewarding, both in a theoretical and a practical sense.
Research and Advances Mar 1 1978

Value orientation of computer science students

Technological and nontechnological value orientations are investigated with special attention to the complexity of value structures. Computer science students, who are closely associated with technology, contrast with social science students, who are often technologically aloof. This is confirmed by the value ratings of 313 students at the University of Minnesota in 1972. Computer science majors were found to have a more complex value structure than social science majors.
Research and Advances Mar 1 1978

Management utilization of computers in American local governments

Traditional concepts of management information systems (MIS) bear little relation to the information systems currently in use by top management in most US local governments. What exists is management-oriented computing, involving the use of relatively unsophisticated applications. Despite the unsophisticated nature of these systems, management use of computing is surprisingly common, but also varied in its extent among local governments. Management computing is most prevalent in those governments with professional management practices where top management is supportive of computing and tends to control computing decisions and where department users have less control over design and implementation activities. Finally, management computing clearly has impacts for top managers, mostly involving improvements in decision information.
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Research and Advances Feb 1 1978

Computer science faculties: the current status of minorities and women

The results of a survey conducted in the fall of 1975 to determine the status of women and minority faculty members in academic computer science are presented. Faculty members were compared with respect to professional background, salaries, teaching load, publication records, and research grants. Analysis of the data indicated that the over-all verdict is one of general equality among women, minorities, and men.
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Research and Advances Feb 1 1978

A method for obtaining digital signatures and public-key cryptosystems

An encryption method is presented with the novel property that publicly revealing an encryption key does not thereby reveal the corresponding decryption key. This has two important consequences: (1) Couriers or other secure means are not needed to transmit keys, since a message can be enciphered using an encryption key publicly revealed by the intented recipient. Only he can decipher the message, since only he knows the corresponding decryption key. (2) A message can be “signed” using a privately held decryption key. Anyone can verify this signature using the corresponding publicly revealed encryption key. Signatures cannot be forged, and a signer cannot later deny the validity of his signature. This has obvious applications in “electronic mail” and “electronic funds transfer” systems. A message is encrypted by representing it as a number M, raising M to a publicly specified power e, and then taking the remainder when the result is divided by the publicly specified product, n, of two large secret primer numbers p and q. Decryption is similar; only a different, secret, power d is used, where e * d ≡ 1(mod (p - 1) * (q - 1)). The security of the system rests in part on the difficulty of factoring the published divisor, n.
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Research and Advances Jan 1 1978

The evolution of the DECsystem 10

The DECsystem 10, also known as the PDP-10, evolved from the PDP-6 (circa 1963) over five generations of implementations to presently include systems covering a price range of five to one. The origin and evolution of the hardware, operating system, and languages are described in terms of technological change, user requirements, and user developments. The PDP-10's contributions to computing technology include: accelerating the transition from batch oriented to time sharing computing systems; transferring hardware technology within DEC (and elsewhere) to minicomputer design and manufacturing; supporting minicomputer hardware and software development; and serving as a model for single user and timeshared interactive minicomputer/microcomputer systems.
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Research and Advances Jan 1 1978

The development of the MU5 computer system

Following a brief outline of the background of the MU5 project, the aims and ideas for MU5 are discussed. A description is then given of the instruction set, which includes a number of features conducive to the production of efficient compiled code from high-level language source programs. The design of the processor is then traced from the initial ideas for an associatively addressed “name store” to the final multistage pipeline structure involving a prediction mechanism for instruction prefetching and a function queue for array element accessing. An overall view of the complete MU5 complex is presented together with a brief indication of its performance.
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Research and Advances Jan 1 1978

The Manchester Mark I and atlas: a historical perspective

In 30 years of computer design at Manchester University two systems stand out: the Mark I (developed over the period 1946-49) and the Atlas (1956-62). This paper places each computer in its historical context and then describes the architecture and system software in present-day terminology. Several design concepts such as address-generation and store management have evolved in the progression from Mark I to Atlas. The wider impact of Manchester innovations in these and other areas is discussed, and the contemporary performance of the Mark I and Atlas is evaluated.
Research and Advances Jan 1 1978

The CRAY-1 computer system

This paper describes the CRAY-1, discusses the evolution of its architecture, and gives an account of some of the problems that were overcome during its manufacture. The CRAY-1 is the only computer to have been built to date that satisfies ERDA's Class VI requirement (a computer capable of processing from 20 to 60 million floating point operations per second) [1]. The CRAY-1's Fortran compiler (CFT) is designed to give the scientific user immediate access to the benefits of the CRAY-1's vector processing architecture. An optimizing compiler, CFT, “vectorizes” innermost DO loops. Compatible with the ANSI 1966 Fortran Standard and with many commonly supported Fortran extensions, CFT does not require any source program modifications or the use of additional nonstandard Fortran statements to achieve vectorization. Thus the user's investment of hundreds of man months of effort to develop Fortran programs for other contemporary computers is protected.

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