OPERATING SYSTEM

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CHAPTER 5
(Operating System)

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• OS is an example of
system software –
software that controls
the system’s hardware,
and which interacts
with the user and
application software.
• In short, the operating
system is the
computer’s master
control program.
OPERATING SYSTEM

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THE OPERATING SYSTEM PERFORMS
THE FOLLOWING FUNCTIONS
• Provides the instructions to display the on-screen
elements with which you interact. Collectively, these
elements are known as the user interface.
• Loads programs (such as word processing and
spreadsheet programs) into the computer’s memory
so that you can use them.
• Coordinates how programs work with the CPU, RAM,
Keyboard, mouse, printer, and other hardware, as
well as with other software.
• Manages the way information is stored on the
received from disks.

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OPERATING SYSTEMS CYCLE

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RUNNING PROGRAMS
• The operating system
provides a consistent
interface between those
programs and other
computer resources such
as memory, a printer, or
another program.
• Programmers write
computer programs with
built – in instructions –
called SYSTEM CALLS – that
request services from the
operating system.

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EXAMPLES OF
OPERATING SYSTEM

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MICROSOFT WINDOWS
• Microsoft Windows is a
family of proprietary
operating systems most
commonly used on
personal computers.
• It is the most common
family of operating
systems for the
personal computer,
with about 90% of the
market share

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• Ken Thompson wrote B,
mainly based on BCPL,
which he used to write
Unix, based on his
experience in the MULTICS
project.
• B was replaced by C, and
Unix developed into a
large, complex family of
inter-related operating
systems which have been
influential in every
modern operating system
UNIX / LINUX

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BSD / DESCENDANTS
• A subgroup of the Unix
family is the
Berkeley Software Distribution
family, which includes
FreeBSD, NetBSD, and
OpenBSD.
• These operating systems
are most commonly
found on webservers,
although they can also
function as a personal
computer OS.

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MAC / OS
• Mac OS X is a line of
partially proprietary
graphical operating
systems developed,
marketed, and sold
by Apple Inc., the
latest of which is pre-
loaded on all
currently shipping
Macintosh computers.

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CONTINUATION:
• Mac OS X is the successor to the original
Mac OS, which had been Apple's primary
operating system since 1984.
• Unlike its predecessor, Mac OS X is a UNIX
operating system built on technology that
had been developed at NeXT through the
second half of the 1980s and up until Apple
purchased the company in early 1997

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PLAN 9
• Programmers at
Bell Labs went on to
develop Plan 9 and
Inferno, which were
engineered for
modern distributed
environments.

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• Plan 9 was designed from the start to be a
networked operating system, and had
graphics built-in, unlike Unix, which added
these features to the design later.
• It is currently released under the
Lucent Public License. Inferno was sold to
Vita Nuova Holdings and has been released
under a GPL/MIT license.
CONTINUATION:

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LINUX AND GNU
• Linux is the generic name
for a UNIX like operating
system that can be used on
a wide range of devices
from supercomputers to
wristwatches. The Linux
kernel is released under
an open source license, so
anyone can read and
modify its code. It has
been modified to run on a
large variety of electronics

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GOOGLE CHROME OS
• Chrome is an O.S. based on
the Linux kernel and
designed by Google. Chrome
targets computer users that
spend most of their time on
the internet—it is technically
only a web browser with no
other applications, and relies
on internet applications used
in the web browser to
accomplish tasks such as
word processing and media
viewing.

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COMPONENTS OF AN
OPERATING SYSTEM

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USER INTERFACE
• Computer receives some
sort of human input
needs a user interface,
which allows a person
to interact with the
computer. While devices
like keyboards, mice
and touch screens make
up the hardware end of
this task, the user
interface makes up the
software for it.

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CONTINUATION:
• The two most common forms of a user
interface have historically been the
Command-line interface, where computer
commands are typed out line-by-line, and
the Graphical user interface, where a visual
environment (most commonly with windows,
buttons, and icons) is

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GRAPHICAL USER INTERFACES
• Most of the modern
computer systems support
graphical user interfaces
(GUI), and often include
them.
• In some computer
systems, such as the
original implementations
of Microsoft Windows and
the Mac OS, the GUI is
integrated into the kernel
.

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THE KERNEL
• With the aid of the
firmware and
device drivers, the
operating system
provides the most
basic level of
control over all of
the computer's
hardware devices.

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CONTINUATION:
• It manages memory access for programs in
the RAM, it determines which programs get
access to which hardware resources, it sets
up or resets the CPU's operating states for
optimal operation at all times, and it
organizes the data for long-term
non-volatile storage with file systems on such
media as disks, tapes, flash memory, etc.

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PROGRAM EXECUTION
• The operating system acts as an interface between
an application and the hardware. The user
interacts with the hardware from "the other
side".
• The operating system is a set of services which
simplifies development of applications. Executing
a program involves the creation of a process by
the operating system. The kernel creates a
process by assigning memory and other
resources, establishing a priority for the process
(in multi-tasking systems), loading program code
into memory, and executing the program.

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INTERRUPTS
• Interrupts are central to operating systems,
as they provide an efficient way for the
operating system to interact with and react
to its environment.
• Interrupt-based programming is directly
supported by most modern CPUs. Interrupts
provide a computer with a way of
automatically saving local register contexts,
and running specific code in response to
events

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MODES
• Modern CPUs support
multiple modes of
operation.
• CPUs with this
capability use at least
two modes: protected
mode and supervisor
mode.

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CONTINUATION:
• The supervisor mode is used by the
operating system's kernel for low level tasks
that need unrestricted access to hardware,
such as controlling how memory is written
and erased, and communication with
devices like graphics cards.
• Protected mode, in contrast, is used for
almost everything else.

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MEMORY MANAGEMENT
• System of memory management is almost never
seen anymore, since programs often contain
bugs which can cause them to exceed their
allocated memory.
• If a program fails it may cause memory used by
one or more other programs to be affected or
overwritten. Malicious programs, or viruses may
purposefully alter another program's memory or
may affect the operation of the operating system
itself. With cooperative memory management it
takes only one misbehaved program to crash the
system.

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VIRTUAL MEMORY
• The use of virtual
memory addressing
(such as paging or
segmentation) means
that the kernel can
choose what memory
each program may use
at any given time,
allowing the operating
system to use the same
memory locations for
multiple tasks.

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DEVICE DRIVER
• A device driver is a specific type of computer
software developed to allow interaction with
hardware devices.
• Typically this constitutes an interface for
communicating with the device, through the
specific computer bus or communications
subsystem that the hardware is connected to,
providing commands to and/or receiving
data from the device, and on the other end,
the requisite interfaces to the operating
system and software applications.

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NETWORKING
• Currently most operating systems support a variety of
networking protocols, hardware, and applications
for using them.
• This means that computers running dissimilar
operating systems can participate in a common
network for sharing resources such as computing,
files, printers, and scanners using either wired or
wireless connections. Networks can essentially allow
a computer's operating system to access the
resources of a remote computer to support the same
functions as it could if those resources were
connected directly to the local computer.

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SECURITY
• A computer being secure depends on a number of
technologies working properly. A modern operating
system provides access to a number of resources,
which are available to software running on the
system, and to external devices like networks via the
kernel.
• External security involves a request from outside the
computer, such as a login at a connected console or
some kind of network connection. External requests
are often passed through device drivers to the
operating system's kernel, where they can be passed
onto applications, or carried out directly.