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Unformatted text preview: itted batch were processed, the operator would
separate the printed output for each job and keep them at the reception counter so
that the programmers could collect them later.
The batch processing mechanism helped in reducing the idle time of a computer
system to a great extent because transition from one job to another did not require
any operator intervention. Another major time saving made possible by batch
processing was reduction in set-up time by batching of similar jobs together by the
operator. For example, if all FORTRAN compilation jobs are batched together, the
system needs to load the FORTRAN compiler only once for processing all these
The obvious question is how the computer separates one job from another from a
batch of jobs for automatic job-to-job transition. Moreover, how does the system
know which compiler or what hardware devices are to be used by a particular job
when there is no operator intervention? To facilitate all these, control statements
and job control languages (JCLs) were introduced along with the concept of batch
processing. The control statements are used by the operating system to identify a
new job and to determine what resources are needed by the job during its
execution. These control statements are written in a language known as the job
control language. Usually every program and data sets are preceded and followed
by JCL statements.
When a program is prepared for a computer run, it is necessary to prepare the job
control statements and place them in proper order along with the program, before
the program is fed to the computer system. Thus, each program has, besides the program itself, a set of instructions called JCL instructions, which instruct the
operating system on the identity and requirements of the job. JCL statements tell
the operating system things such as the name of the job, the user's name and
account number, the I/O devices to be used during processing, the assembler or
compiler to be used if language translation is required, and so on. Figure 14.2
shows a sample deck of cards prepared for the compilation and execution of a
COBOL program in a...
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This document was uploaded on 04/07/2014.
- Spring '14