Programs used for commercial data processing

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Unformatted text preview: batch processing system. Notice from the figure that in order to distinguish a control card from data or program cards, they are identified by a special character or pattern on the card. Several systems used the dollar-sign character ($) in the first column to identify a control card, while IBM's JCL used slash marks (//) in the first two columns. Other systems used some other characters or codes. The basic idea in selection of these special characters or codes was that no program or data card should have these characters or code. SEND Data for program $RUN $LOAD COBOL program $COBOL $JOB, ONGC05839, USER=SINHA Multiprogramming In case of both manual loading and batch processing of jobs, the jobs are loaded into the system and processed one at a time. That is, once loaded, a job will remain in the main memory until its execution is completed and the next job will be loaded only after the completion of the previous job. As shown in Figure 14.3, in such a situation, the job which is currently loaded and is being executed will be the sole occupant of the user's area of the main memory (the operating system always resides in a part of the main memory) and it will have the CPU exclusively available for itself. The situation shown in Figure 14.3 is that of a uniprogramming system in which only one job is processed by the system at a time and all the system resources are exclusively available for the job until it completes. It was observed that a job does not need the CPU for the entire duration of its processing. This is because in addition to doing computation (for which CPU is needed), a job often needs to perform I/O operations (such as reading or writing some data to a tape or disk, waiting for some data to be input from the keyboard, and printing some results) during the course of its processing. In fact, depending on the CPU utilization during the course of processing, jobs are broadly classified into the following two types: 1. CPU-bound jobs. These jobs mostly perf...
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This document was uploaded on 04/07/2014.

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