Operating Systems

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CSCA0201
FUNDAMENTALS OF COMPUTING
Chapter 6
Operating Systems
CSCA0201
FUNDAMENTALS OF COMPUTING
Chapter 5
Storage Devices
CSCA0201
FUNDAMENTALS OF COMPUTING
Chapter 7
Operating Systems

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Chapter 7 Operating Systems
Operating Systems
• An operating system or OS is a software program
that enables the computer hardware to communicate
and operate with the computer software.
• It is also the program that manages all the other
programs in a computer.
• The operating system is the most important program
that runs on a computer.
• Operating system is an interface between computer
and user.

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Chapter 7 Operating Systems
Components of Operating System
• Kernel
• Program execution
• Interrupts
• Memory management
• Virtual memory
• Multitasking
• Disk access and file systems
• Device drivers
• Networking
• Security
• User interface

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Chapter 7 Operating Systems
Components of Operating System
Kernel
• The kernel provides the most basic level
of control over all of the computer's
hardware devices.
• 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.
• 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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Chapter 7 Operating Systems
Components of Operating System
Program Execution
• The operating system provides an interface between an
application program and the computer hardware, so that
an application program can interact with the hardware
only by obeying rules and procedures programmed into
the operating system.
• The operating system is also a set of services which
simplify development and execution of application
programs.
• Executing an application program involves the creation of
a process by the operating system kernel which assigns
memory space and other resources, etc…

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Chapter 7 Operating Systems
Components of Operating System
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.
• Interrupts provide a computer with a way of automatically saving
local register contexts, and running specific code in response to
events.
• Even very basic computers support hardware interrupts, and
allow the programmer to specify code which may be run when
that event takes place.

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Chapter 7 Operating Systems
Components of Operating System
Memory Management
• Memory management handles or manages primary memory
(RAM) and moves processes back and forth between main
memory and disk during execution.
• Memory management keeps track of each and every memory
location, regardless of either it is allocated to some process or it
is free.
• It checks how much memory is to be allocated to processes.
• It decides which process will get memory at what time. It tracks
whenever some memory gets freed or unallocated and
correspondingly it updates the status.

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Chapter 7 Operating Systems
Components of Operating System
Disk Access and File Systems
• Access to data stored on disks is a central
feature of all operating systems.
• Computers store data on disks using files,
which are structured in specific ways in
order to allow for faster access, higher
reliability, and to make better use of the
drive's available space.
• The specific way in which files are stored
on a disk is called a file system, and
enables files to have names and
attributes.
• It also allows them to be stored in a
hierarchy of directories or folders arranged
in a directory tree.

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Chapter 7 Operating Systems
Components of Operating System
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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Chapter 7 Operating Systems
Components of Operating System
Networking
• Client/server networking allows a program on a computer, called
a client, to connect via a network to another computer, called a
server.
• Servers offer (or host) various services to other network
computers and users.
• Computers that 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.

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Chapter 7 Operating Systems
Components of Operating System
Security
• Security refers to providing a protection
system to computer system resources
such as CPU, memory, disk, software
programs and most importantly
data/information stored in the computer
system.
• If a computer program is run by an
unauthorized user, then he/she may cause
severe damage to computer or data stored
in it.
• So a computer system must be protected
against unauthorized access, malicious
access to system memory, viruses, worms
etc.

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Chapter 7 Operating Systems
Components of Operating System
User Interface
• Every computer that is to be operated by an individual requires
a user interface.
• The user interface is usually referred to as a shell and is
essential if human interaction is to be supported.
• The user interface views the directory structure and requests
services from the operating system that will acquire data from
input hardware devices, such as a keyboard, mouse or credit
card reader, and requests operating system services to display
prompts, status messages and such on output hardware
devices, such as a video monitor or printer.

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Chapter 7 Operating Systems
Types of Operating System
• Real-time
• Batch
• Multi-user / Single-user
• Multi-tasking / Single-tasking
• Distributed
• Embedded

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Chapter 7 Operating Systems
Types of Operating System
Real-Time / Batch
• A real-time operating system is a multitasking
operating system that aims at executing real-time
applications.
• Responds to input instantly.
• The users of a batch operating system do not
interact with the computer directly.
• Each user prepares his job on an off-line device like
punch cards and submits it to the computer
operator.
• To speed up processing, jobs with similar needs are
batched together and run as a group.

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Chapter 7 Operating Systems
Types of Operating System
Multi-user / Single-user
 A multi-user operating system allows multiple users
to access a computer system concurrently.
 Time-sharing system can be classified as multi-user
systems as they enable a multiple user access to a
computer through the sharing of time.
 Single-user operating systems, as opposed to a
multi-user operating system, are usable by a single
user at a time.

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Chapter 7 Operating Systems
Types of Operating System
Multi-tasking / Single-tasking
 When a single program is allowed to run at a time,
the system is grouped under a single-tasking system
 While in case the operating system allows the
execution of multiple tasks at one time, it is
classified as a multi-tasking operating system

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Chapter 7 Operating Systems
Types of Operating System
Distributed
 A distributed operating system manages a group of
independent computers and makes them appear to
be a single computer.
 The development of networked computers that could
be linked and communicate with each other, gave
rise to distributed computing.

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Chapter 7 Operating Systems
Types of Operating System
Embedded
 Embedded operating systems are designed to be
used in embedded computer systems.
 They are designed to operate on small machines
like PDAs with less autonomy.
 They are able to operate with a limited number of
resources.

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Chapter 7 Operating Systems
User Interface
• A program that controls a display for the user
(usually on a computer monitor) and that allows the
user to interact with the system.
• The user interface allows the user to communicate
with the operating system.

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Chapter 7 Operating Systems
User Interface
• The user interface provides means of:
– Input - allowing the users to manipulate a
system
– Output - allowing the system to indicate the
effects of the users' manipulation.

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Chapter 7 Operating Systems
User Interface
There are two types of user interface:
• Command line interface
• Graphical user interface

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Chapter 7 Operating Systems
User Interface
Command Line Interface (CLI)
• A command-line interface is a mechanism for
interacting with a computer operating system or
software by typing commands to perform specific
tasks.
• This method of instructing a computer to perform a
given task is referred to as "entering" a command.
• Accept input via keyboard only.
• Not suitable for beginners.

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Chapter 7 Operating Systems
User Interface
Command Line Interface (CLI)

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Chapter 7 Operating Systems
User Interface
Graphical User Interface (GUI)
• Is a type of user interface which allows people to
interact with computer with images rather than text
commands.
• Accept input via keyboard and pointing devices.
• Easy to learn.

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Chapter 7 Operating Systems
User Interface
Elements of Graphical User Interface
• Desktop
• Pointer
• Icons
• Windows
• Menus
• Tab

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Chapter 7 Operating Systems
Types of User Interface
Desktop
• The area on the display screen where icons are
grouped is often referred to as the desktop because
the icons are intended to represent real objects on a
real desktop.

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Chapter 7 Operating Systems
Types of User Interface
Desktop

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Chapter 7 Operating Systems
User Interface
Pointer
• A symbol that appears on the
display screen and that you
move to select objects and
commands.
• Usually, the pointer appears
as a small angled arrow.

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Chapter 7 Operating Systems
Types of User Interface
Icons
• They are a quick way to
execute commands, open
documents, and run
programs.
• Icons are also very useful
when searching for an
object in a browser list,
because in many operating
systems all documents
using the same extension
will have the same icon.

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Chapter 7 Operating Systems
Types of User Interface
Windows
• A window is an area on the screen that displays
information, with its contents being displayed
independently from the rest of the screen.
• Used to divide the screen into different areas.
• Multiple windows can also be open at one time, in
which case each window can display a different
application or file

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Chapter 7 Operating Systems
Types of User Interface
Windows
Windows

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Chapter 7 Operating Systems
Types of User Interface
Menus
• Menus allow the user to execute commands by
selecting from a list of choices.
• Options are selected with a mouse or other pointing
device within a GUI.
• Two types of menu:
– Pull-down menu
– Pop-up menu

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Chapter 7 Operating Systems
Types of User Interface
Menus
Pull-down Menu
Pop-up Menu

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Chapter 7 Operating Systems
Types of User Interface
Tab
• A tab is typically a rectangular small box which
usually contains a text label or graphical icon
associated with a view pane.
• When activated the view pane, or window, displays
widgets associated with that tab; groups of tabs allow
the user to switch quickly between different widgets.
• This is used in the web browsers Firefox, Internet
Explorer, Opera, and Safari.

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Chapter 7 Operating Systems
Types of User Interface
Tab
Tabs

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Chapter 7 Operating Systems
Examples of Operating System
• MS DOS
• MS Windows
• Mac OS
• Linux
• Ubuntu
• Solaris
• Android
• iOS