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Operating Systems
4.1 What is an operating
system?
4.2 Classifications of operating
systems
4.3 Types of operating system
4.4 Functions and services.
Operating System
An operating system is complex, so it is
difficult to give a simple universal definition.
Instead, here are some common definitions:
• A program that controls the execution of
application programs
• An interface between applications and
hardware
• An operating system is an interface between
the hardware of a computer and the user
(programs or humans).
Operating System
• 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.
• 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.
Operating System Objectives
• Convenience
– Makes the computer more convenient to
use
• Efficiency
– Allows computer system resources to be
used in an efficient manner
• Ability to evolve
– Permit effective development, testing, and
introduction of new system functions
without interfering with service
Layers of Computer System
Classification of Operating Systems
Operating Systems can be classified according to
how they work.
• Batch Processing operating system
• Time Sharing operating system
• Real-time operating system
• Multi-user operating system
• Multi-tasking operating system
• Distributed operating system
• Embedded operating systems.
Modern operating systems include: OS, Linux,
Android, BSD, Mac OS X and Microsoft Windows.
Types of Operating Systems
• Mainframe operating systems: MVS
• Server operating systems: FreeBSD, Solaris
• Multiprocessor operating systems: Cellular
IRIX
• Personal computer operating systems:
Windows, Unix
• Real-time operating systems: VxWorks
• Embedded operating systems
• Smart card operating systems
Some operating systems can fit into more
than one category
Types of Operating Systems
• Real-time operating system
– Very fast small OS
– Built into a device
– Respond quickly to user input
– MP3 players, Medical devices
Types of Operating Systems
• Single user/Single tasking OS
– One user works on the system
– Performs one task at a time
– MS-DOS and Palm OS
– Take up little space on disk
– Run on inexpensive computers
Single Tasking
• Operating System cannot be able to take control back from the running process/task/application
• In case if a process call an I/O Instruction then Processor must wait for I/O instruction to complete before preceding
Types of Operating Systems
• Single user/Multitasking OS
– User performs many tasks at once
– Most common form of OS
– Windows XP and OS X
– Require expensive computers
– Tend to be complex
Multitasking
• Operating System can take control back from the running process and can give it to other.
• When one job needs to wait for I/O, the processor can switch to the other job
Types of Operating Systems
• Multi user/Multitasking OS
– Many users connect to one computer
– Each user has a unique session
– UNIX, Linux, and VMS
– Maintenance can be easy
– Requires a powerful computer
Multi user/Multi tasking OS
Services Provided by
the Operating System
• Program development
– Editors and debuggers
• Program execution
• Access to I/O devices
• Controlled access to files
• System access
Services Provided by
the Operating System
• Error detection and response
– internal and external hardware errors
• memory error
• device failure
– software errors
• arithmetic overflow
• access forbidden memory locations
– operating system cannot grant request of
application
Services Provided by
the Operating System
• Accounting
– collect statistics
– monitor performance
– used to anticipate future enhancements
– used for billing users
7A-19
Functions of Operating Systems
manage programs
start up the computeradminister security
monitor performance and provide housekeeping services
manage memory
7A-20
Functions of Operating Systems
control a network
access the Web
schedule jobs and
configure devices
provide user
interface
7A-21
Functions of Operating Systems
The basic functions that an Operating System should provide include (but not limited to):
• Provide a user interface
• Run programs
• Manage hardware devices
– CPU and Process Management
– Memory Management
– I/O Management
– Information And Storage Management
– Network Management
• Organize file storage
• Security
• Resource Allocation and Accounting
Providing a User Interface
• User interface
– How a user interacts with a computer
– Require different skill sets
Providing a User Interface
• Graphical user interface (GUI)
– Most common interface
• Windows, OS X, Gnome, KDE
– Uses a mouse to control objects
– Uses a desktop metaphor
– Shortcuts open programs or documents
– Open documents have additional objects
– Task switching
– Dialog boxes allow directed input
Graphical User Interface
Providing a User Interface
• Command line interfaces
– Older interface
• DOS, Linux, UNIX
– User types commands at a prompt
– User must remember all commands
– Included in all GUIs
Command Line Interface
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DOS plus Windows 3.1
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Windows 95
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Windows XP
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Macintosh
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Mac OS X
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UNIX with X-Windows
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Microsoft Windows 8
Running Programs
• Many different applications supported
• System call
– Provides consistent access to OS features
• Share information between programs
– Copy and paste
– Object Linking and Embedding
Managing Hardware
• Programs need to access hardware
• Interrupts
– CPU is stopped
– Hardware device is accessed
• Device drivers control the hardware
Organizing Files and Folders
• Organized storage
• Long file names
• Folders can be created and nested
• All storage devices work consistently
Operating Systems
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