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Unformatted text preview: me is usually not a suitable measure for
interactive systems, because in an interactive system a process can produce some
output fairly early during its execution and can continue executing while previous
results are being output to the user. Thus another measure used in case of
interactive systems is response time, which is the interval from the time of submission of a job to the system for processing to the time the first response for
the job is produced by the system.
In any computer system, it is desirable to maximize throughput and to minimize
turnaround time and response time.
A process (also called job) is a program in execution. The main objective of the
process management module of an operating system is to manage the processes
submitted to the system in such a manner so as to minimize the idle time of the
various processors (CPU, I/O processors, etc.) of the computer system. In this
section, we will learn about some of the mechanisms commonly used in modern
operating systems to achieve this objective. We will also see how these
mechanisms have gradually evolved from the early days of computers.
Process Management in Early Systems
In early computer systems, a job was typically executed in the following manner:
1. A programmer would first write the program on paper.
2. It was then punched on cards or paper tape along with its data.
3. The deck.of cards or the paper tape containing the program and data was then
submitted at tin reception counter of the computer centre.
4. An operator would then take the card deck or paper tape and manually load it
into the system from card reader or paper tape reader. The operator was also
responsible for loading any other software resource (such as a language compiler)
or setting hardware devices required for the execution of the job. Before loading
of the job, the operator had to use the front panel switches of the compute system
to clear the main memory to remove any data remaining from the previous job.
5. The operator would then set the appropriate switches in the front panel to run
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- Spring '14