A
batch is a sequence of user jobs. Early computers were the large machines that
run from a consol. The input devices used were tape drivers and card readers.
The common output devices were card punchers and line printers.
The
users of batch systems did not interact directly with the computer systems. Rather,
the user prepared a job, which consist of program, data and control information
and then submitted it to the computer operator.
A
computer operator forms a batch by arranging user jobs in a sequence and
inserting JCL commands (Job Control Language) to automate
various activities of the operating system. JCL commands include
commands for marking of job beginning and end, commands for loading and execution of program, and commands to announce resource needs etc. After forming a batch, the operator submits it to the operating system for processing.
commands for marking of job beginning and end, commands for loading and execution of program, and commands to announce resource needs etc. After forming a batch, the operator submits it to the operating system for processing.
The
primary function of the batch processing operating system is to implement the
processing of a batch of jobs without requiring any intervention of the
operator. The operating system achieves this by making an automatic transition
from the execution of one job to that of the next job in the batch.
A
memory resident portion of the batch processing operating system, called batch monitor, reads, interprets and
executes the JCL commands. The batch monitor is responsible for implementing
various functions of the batch processing operating system.
The
tasks of batch monitor can be classified into three functions:
1. Scheduling
2. Memory management and
3. Sharing and protection
Batch
monitor performs a FCFS (First-Come-First-Serve) scheduling by always
initiating the next job in the batch.
In a batch processing system, the memory is divided
into two at any time- the system area and the user area. In order to provide
maximum space to the user program, an overlay
structure is used to store the monitor program in the system area. The
resident part of the monitor is permanently situated in the memory, while the
transient parts are loaded into the transient area whenever required.
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| Memory partitioning in batch processing system |
Disadvantages of the batch
processing system
- Higher turnaround time
- Under-utilization of the system resources
- Allows no interaction between user and executing program
Turnaround time of a job is the
time since its submission to the system to the time its output becomes
available to the user.
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