Page 26 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes Though all the jobs are processed simultaneously, this too can lead to loss of security or protection.
Let us suppose that there are two users A and B. User A creates a file of his own. User B deletes
the file created by User A. There are so many other similar instances that can occur in our day to
day life. So, the files and other data of all the users should be protected against unauthorized
usage. In order to avoid such loss of protection, each user is bound around certain rules and
regulations. This takes the form of a set of control statements, which every user is required to
follow.

Multiprogramming Operating System

The objective of a multiprogramming operating system is to increase the system utilization
efficiency. The batch processing system tries to reduce the CPU idle time through operator
interaction. However, it cannot reduce the idle time due to IO operations. So, when some IO is
being performed by the currently executing job of a batch, the CPU sits idle without any work
to do. Thus, the multiprogramming operating system tries to eliminate such idle times by
providing multiple computational tasks for the CPU to perform. This is achieved by keeping
multiple jobs in the main store. So, when the job that is being currently executed on the CPU
needs some IO, the CPU passes its requirement over to the IO processor. Till the time the IO
operation is being carried out, the CPU is free to carry out some other job. The presence of
independent jobs guarantees that the CPU and IO activities are totally independent of each
other. However, if it was not so, then it could lead to some erroneous situations leading to some
time-dependent errors. Some of the most popular multiprogramming operating systems are:
UNIX, VMS, WindowsNT, etc.
A multiprogramming supervisor has a very difficult job of managing all the activities that take
place simultaneously in the system. He has to monitor many different activities and react to a
large number of different situations in the course of working. The multiprogramming supervisor
has to look through the following control functions:

Time Sharing or Multitasking System

Time sharing, or multitasking, is a logical extension of multiprogramming. Multiple jobs are
executed by the CPU switching between them, but the switches occur so frequently that the users
may interact with each program while it is running.

An interactive, or hands-on, computer system provides online communication between the user
and the system.

Did u know? The user gives instructions to the operating system or to a program directly,
and receives an immediate response.

Usually, a keyboard is used to provide input, and a display screen (such as a cathode-ray tube
(CRT), or monitor) is used to provide output. When the operating system finishes the execution
of one command, it seeks the next "control statement" not from a card reader, but rather from the
user's keyboard. The user gives a command, waits for the response, and decides on the next
command, based on the result of the previous one. The user can easily experiment, and can see
results immediately. Most systems have an interactive text editor for entering programs, and an
interactive debugger for assisting in debugging programs.
If users are to be able to access both data and code conveniently, an online file system must be
available. A file is a collection of related information defined by its creator. Commonly, files

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