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# Control in Time-Sharing Systems

Fermin Caro del Castillo

6043 Westridge Lane

Fort Worth, Texas 76116

"A time-sharing installation (like every computer environment) is exposed to the seven major dangers: fire, water, theft, fraud, sabotage, equipment malfunctions, and human errors."

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## Introduction

This article has as its main objective to furnish and define some methods and provisions for control and security in a computer time-sharing environment.

It is evident that computer time-sharing has become very popular during recent years. More and more confidential information is being handled by these systems, creating an urgent need for strong measures of control and security.

## Description of the System

The service provided by a single computer to many telecommunications terminals has been called "computer time-sharing". With this type of service each user shares simultaneously in the processing capabilities of the central processor. This new computer facility makes this service available to small companies and/or other users who have little need for their own computer.

Computing services that may go under the heading of time-sharing include:

Commercial computing; text editing; databank information retrieval services; application services such as colleges' records, inventory control, payrolls of small companies, and account receivables; administrative messages; switching and collection services; and more.

Among the great number of time-sharing users are hospitals (Welch Hospital, one of the biggest in Europe, has acquired the large ICL 1904S computer with 7020 terminals), banks (Gosbank, the national bank of the USSR, has ordered two large-scale Honeywell series 600 with 100 terminals), schools and colleges (British schools and colleges have started using terminals), airlines (Continental Airlines uses the Sonic 360 reservation system with 550 online terminals).

## Trends

The growth in computer time-sharing has been phenomenal in recent years in spite of a short business recession between 1970 and 1972. Time sharing was a broker's dream in the '60s; many companies realized its potential, entered the market, and failed because of: one, strong competitive pressure, and two, because of the countless thefts and violations suffered. The highly competitive situation benefited the user in regard to pricing, but the offsetting consequence of lower profits caused a high casualty rate among these companies. As a result, the number of time-sharing firms dropped from 150 to 50 between 1969 and 1972.

A few of the companies which survived and which account for most of today's time-sharing business are Rapidata Corporation, Teletype Corporation (a subsidiary of ATGT), Tymeshare Incorporated (the largest independent firm and second only in size to IBM and Honeywell time-sharing operations), and IBM

Jerry Dreyer, executive president of ADAPSO, an association of data processing service organizations estimates that one time-sharing company out of three was profitable in 1971, two out of five in 1972, and probably three out of six in 1973. Nowadays, this computer facility is coming back to its original trend, and it is expected that the number of computers with terminals will grow from 32% at the end of 1971 to 45% at the end of 1975, with the average central processing unit driving 15 to 20 terminals.

One consultant, Creative Strategies of Palo Alto, California, predicts that time-sharing sales by 1976 will increase to 2 billion from 331 million last year. By 1975, says ADAPSO's Dreyer, time-sharing will account for 1/3 of the $4.5 billion computer services industry.

## Technological Advances

Most important technological advances have been achieved recently on on-line terminals linked to central processors. Some of the improvements made include solid state keyboards, which have greater reliability and lower cost; visual display methods, which incorporate more capacity, economy, and aesthetic appeal; non-impact printing techniques, which provide faster, quieter and more reliable operations; improved lower cost memories; more powerful logic capability; and faster and more accurate modern techniques and improvements in central processor software.

This is only the beginning. It is foreseen that in the future the equipment itself will change in nature and will probably not be recognizable as terminals per se. Rather, terminals will be modular systems consisting of the required input/output functions for specific jobs, built around basic controller and communication interfaces; in many instances, terminals will become special purpose devices.

## Hazards

A time-sharing installation, like every computer environment, is exposed to the seven major dangers of fire, water, theft, fraud, sabotage, EDP equipment malfunctions, and human errors. Fire is considered to be the greatest threat to magnetic tapes. Water does not constitute an important hazard to magnetic tapes, but it does to computer installa-