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OS
McGraw-Hill
1
©The McGraw-Hill Companies, Inc., 2000
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7.2
Operating system is a system that
provides interface between hardware and
user.
Os is a software.
Os is system software.
A computer is a system composed of two major
components: hardware and software. Computer
hardware is the physical equipment. Software is the
collection of programs that allows the hardware to do its
job. Computer software is divided into two broad
categories: the operating system and application
programs (Figure 7.1). Application programs use the
computer hardware to solve users’ problems. The
operating system, on the other hand, controls the access
to hardware by users.
7.3
Figure 7.1 A computer system
7.4
7-1 INTRODUCTION
An operating system is complex, so it is difficult to
give a simple universal definition. Instead, here are
some common definitions:
 An operating system is an interface between the hardware
of a computer and the user (programs or humans).
 An operating system is a program (or a set of programs)
that facilitates the execution of other programs.
 An operating system acts as a general manager supervising
the activity of each component in the computer system.
7.5
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An operating system is an interface between the
hardware of a computer and the user
(programs or humans)
that facilitates the execution of other programs
and the access to hardware and software resources.
Two major design goals of an operating system are:
❑ Efficient use of hardware.
❑ Ease of use of resources.
7.6
Multitasking
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7.7
- Tasks sharing a common resource (like 1
CPU)
In computing, multitasking is a method by
which multiple tasks, also known as
processes, share common processing
resources such as a CPU. With a
multitasking OS, such as Windows XP, you
can simultaneously run multiple
applications.
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7.8
Multitasking refers to the ability of the OS to quickly
switch between each computing task to give the
impression the different applications are executing
multiple actions simultaneously.
As CPU clock speeds have increased steadily over time,
not only do applications run faster, but OSs can switch
between applications more quickly. This provides better
overall performance. Many actions can happen at once
on a computer, and individual applications can run
faster.
Single Core
7.9
Multicore
7.10
Multithreading
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7.11
Multithreading extends the idea of multitasking into applications, so
you can subdivide specific operations within a single application into
individual threads. Each of the threads can run in parallel. The OS
divides processing time not only among different applications, but
also among each thread within an application.
In a multithreaded National Instruments LabVIEW program, an
example application might be divided into four threads - a user
interface thread, a data acquisition thread, network communication,
and a logging thread. You can prioritize each of these so that they
operate independently. Thus, in multithreaded applications, multiple
tasks can progress in parallel with other applications that are
running on the system.
7.12
Time-sharing systems
To
use
computer
system
resources
efficiently,
multiprogramming was introduced. The idea is to hold
several jobs in memory at a time, and only assign a resource
to a job that needs it on the condition that the resource is
available.
Multiprogramming brought the idea of time sharing:
resources could be shared between different jobs, with each
job being allocated a portion of time to use a resource.
Because a computer is much faster than a human, time
sharing is hidden from the user—each user has the
impression that the whole system is serving them
exclusively.
7.13
User interface
Each operating system has a user interface, a program that
accepts requests from users (processes) and interprets them
for the rest of the operating system. A user interface in some
operating systems, such as UNIX, is called a shell. In others,
it is called a window to denote that it is menu driven and has
a GUI (graphical user interface) component.
7.14
Multiprogramming
In multiprogramming, more than one program is in memory
at the same time, and they are executed concurrently, with
the CPU switching rapidly between the programs.
Figure 7.5 Multiprogramming
7.15