Transcript File - Amplify PGD(Telecom Managment)

Lesson 1:
Operating System Basics
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What is an Operating System?
 OS = Operating System
 A program that controls the
of application programs.
execution
 An interface between applications and
hardware.
 Makes the computer more convenient to
use
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What is an Operating system?
 Manages the resources of a computer
and controls the way they are used.
 Allows resources to be used in an
efficient manner.
 Examples of OS’s?
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Where are OS’s used?
 In more and more places!
 Desktop and Server Computers
 DOS + Windows 95/98/ME
 Windows NT/2000/XP
 Free Unix variants: Linux, FreeBSD,
NetBSD, etc.
 Commercial Unix variants: Solaris, HPUX, AIX, etc.
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Where are OS’s used?






MacOS
Some Game Consoles
Xbox: Cut-down Windows 2000
Personal Digital Assistants (PDAs)
PalmOS
Windows CE Windows Mobile
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Where are OS’s used?





Embedded Linux
Mobile Phones
Symbian OS
Windows Mobile
Cars (fancy ones)
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Where are OS’s used?





In the future also:
Digital Cameras (fancy ones)
MP3 Players (iPods, etc.)
Refrigerators!
Others?
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Layers of a Computer System
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Services And System Calls
User Program
(requests service) from
kernel
Type,
Data details
Are sent
Service,data
and
Status returned
UNIX system kernel
(provides
services) to
The user
Services offered and system calls
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Services Provided by the OS
 Program execution
 Access to Input/Output (I/O)
devices
 Disks, screens, keyboards, mice
 Printers, cameras, speakers, etc.
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Services Provided by the OS







Controlled access to files
System access
Sometimes: Program development
Compilers, editors and debuggers
Error detection and response
Internal and external hardware errors
Memory errors
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Services Provided by the OS
Device failures
Software errors
Arithmetic overflow
Division by zero
Access to forbidden memory locations
(why?)
 Operating system cannot grant request
of application





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Operating System as Software
 The OS functions the same way as
ordinary computer software
 It is a program that is executed …
… but it has special privileges
 The OS relinquishes control of the
processor to execute other
programs
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Functions of Operating Systems
 Provide a user interface
 Run programs
 Manage hardware devices
 Organized file storage
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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
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Types of Operating Systems
 Single user/Single tasking OS


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

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
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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
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Multi user/Multi tasking OS
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Providing a User Interface
 User interface
 How a user interacts with a
computer
 Require different skill sets
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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
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Contd:
 Shortcuts open programs or
documents
 Open documents have
additional objects
 Task switching
 Dialog boxes allow directed
input
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Graphical User Interface
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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
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Managing Hardware
 Programs need to access
hardware
 Interrupts
 CPU is stopped
 Hardware device is accessed
 Device drivers control the
hardware
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Organizing Files and Folders
 Organized storage
 Long file names
 Folders can be created and
nested
 All storage devices work
consistently
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Enhancing an OS
 Utilities
 Provide services not included
with OS
 Goes beyond the four functions
 Firewall, anti-virus and
compression
 Prices vary
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Enhancing an OS
 Backup software
 Archives files onto removable
media
 Ensures data integrity
 Most OS include a backup
package
 Many third party packages exist
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Backup Software
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Enhancing an OS
 Anti-virus software
 Crucial utility
 Finds, blocks and removes
viruses
 Must be updated regularly
 McAfee and Norton Anti-Virus
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Enhancing an OS
 Firewall
 Crucial utility
 Protects your computer from
intruders
 Makes computer invisible to
hackers
 Zone Labs is a home firewall
 Cisco sells hardware firewalls
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UNIX
 Unix is a multi-user, multi-tasking
operating system.
 You can have many users logged
into a system simultaneously, each
running many programs.
 It's the kernel's job to keep each
process and user separate and to
regulate
access
to
system
hardware, including cpu, memory,
disk and other I/O devices.
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History of UNIX
 First Version was created in Bell
Labs in 1969.
 Some
of
the
Bell
Labs
programmers who had worked on
this project, Ken Thompson, Dennis
Ritchie, Rudd Canaday, and Doug
McIlroy designed and implemented
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History of UNIX
 the first version of the Unix File
System on a PDP-7 along with a
few utilities. It was given the name
UNIX by Brian Kernighan.
 00:00:00 Hours, Jan 1, 1970 is
time zero for UNIX. It is also called
as epoch.
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History of UNIX
 1973 Unix is re-written mostly
in
C,
a
new
language
developed by Dennis Ritchie.
 Being written in this high-level
language greatly decreased the
effort needed to port it to new
machines.
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History of UNIX
 1977 There were about 500
Unix sites world-wide.
 1980
BSD
4.1
(Berkeley
Software Development)
 1983 SunOS, BSD 4.2, System
V
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History of UNIX
 1988
AT&T
and
Sun
Microsystems jointly develop
System V Release 4 (SVR4).
This
later
developed
into
UnixWare and Solaris 2.
 1991 Linux was originated.
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What is LINUX
 Linux is a free Unix-type operating
system originally created by Linus
Torvalds with the assistance of
developers around the world.
 It originated in 1991 as a personal
project of Linus Torvalds, a Finnish
graduate student.
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What is LINUX
 The Kernel version 1.0 was
released in 1994 and today the
most recent stable version is 2.6.9
 Developed under the GNU General
Public License , the source code for
Linux
is
freely
available
to
everyone.
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LINUX Distributions
 Mandrake:
http://www.mandrakesoft.com/
 RedHat: http://www.redhat.com/
 Fedora: http://fedora.redhat.com/
 SuSE/Novell: http://www.suse.com/
 Debian: http://www.debian.org/
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Red Hat
 Red Hat Enterprise Linux is a
Enterprise
targeted
Operating
System. It based on mature Open
Source technology and available at
a cost with one year Red Hat
Network subscription for upgrade
and support contract.
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UNIX Structure
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Components of a Linux System
 Like most UNIX implementations,
Linux is composed of three main
bodies of code; the most important
distinction between the kernel and
all other components
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Kernel
 Portion of operating system that is
always in main memory
 Contains most-frequently used
functions
 Also called the nucleus
 Good performance of the kernel is
very important
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Components of a Linux System (Cont.)
 The kernel is responsible for
maintaining the important
abstractions of the operating
system.
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Components of a Linux System (Cont.)
 Kernel code executes in kernel
mode with full access to all the
physical resources of the
computer.
 All kernel code and data
structures are kept in the same
single address space.
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Components of a Linux System (Cont.)
 The system libraries define a
standard set of functions through
which applications interact with the
kernel, and which implement much
of the operating-system
functionality that does not need the
full privileges of kernel code.
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Shell
 Shell is the command interpreter.
 It is a interface between a user and
the system.
 The kernel activates an interactive
program called shell for each user
logged into the system.
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Shell
 Shells provide a way to separate
users or tasks from each other.
 Kernel maintains a unified overall
control.
 Shell provides a prompt like $ or %.
 This is called the command line
interface of the shell.
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Shell
 The user can type any valid
UNIX/Linux command.
 Can run a shell script and press
enter to intimate the shell about
the task to perform.
 The shell interprets the typed
command and searches a
predefined path for the executable
file by the name of the command
typed.
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Shell
 It checks the syntax of the
commands and if all is fine, starts
the corresponding executable
running and goes into waiting mode.
 After the command finishes
executing, it exits and control is
returned to the shell.
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Shell
 A shell prompt is returned to the
user.
 Actual fetching and returning of
data at the request of the shell is
done by the kernel.
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Before Operating Systems…
 Serial Processing
 No operating system
 Machines run from a console with
display lights and toggle switches,
input device, and printer.
 Schedule time
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Before Operating Systems…
 Setup included loading the
compiler, source program, saving
compiled program, and loading and
linking.
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Uniprogramming
 Uniprogramming
 Processor must wait for I/O
instruction to complete before
preceding.
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Uniprogramming
 But! Processors are much faster
than I/O devices… inefficient use
of CPU
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Multiprogramming
 When one job needs to wait for
I/O, the processor can switch to
the other job.
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Multiprogramming
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Example Effects
Uniprogramming
Processor use
22%
Memory use
30%
Disk use
33%
Printer use
33%
Elapsed time
30 min.
Throughput rate
6 jobs/hr
Mean response time 18 min.
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Multiprogramming
43%
67%
67%
67%
15 min.
12 jobs/hr
10 min.
Achievements in OS Research
 Processes
 Memory management
 Information protection and
security
 Scheduling and resource
management
 System structure
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Processes
 A program in execution
 An instance of a program running on a
computer
 The entity that can be assigned to and
executed on a processor
 A unit of activity characterized by a
single sequential thread of execution
 a current state
 an associated set of system resources
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Processes
 Consists of three components
 An executable program, i.e., some
code
 Associated data needed by the
program
 Execution context of the program
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Processes
 All information the operating
system needs to manage the
process.
 e.g., who owns the process, which
priority does it have, what
resources does it currently ‘own’.
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OS Support for Processes
 Creating, destroying, starting,
stopping,setting priorities, …
 Process synchronisation
 Semaphores (wait/signal)
 Monitors
 Deadlock detection
 Inter-process communication
 Shared memory
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Processes in Linux
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Modern Operating Systems
 Multithreading
• Each process is divided into threads that can
run simultaneously.
 Thread
•
•
Dispatchable unit of work
Executes sequentially and is interruptible.
 A process is a collection of one or
more threads
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Modern Operating Systems
 Symmetric multiprocessing.
 There are multiple processors.
 These processors share same main
memory and I/O facilities.
 All processors can perform the
same functions.
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Modern Operating Systems
 Distributed operating systems
• Provides the illusion of a single main
memory and single secondary
memory space.
• Distributed shared memory
• Distributed file systems
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Example OS: PalmOS
•Used for PalmPilot PDAs
and successors.
• Multitasking since
PalmOS 5.
• CPUs: Intel XScale,
Texas Instruments
OMAP, Motorola
Dragonball MX
• Wireless: 802.11b,
Bluetooth, GSM, CDMA
• 320×320+ displays
Good battery utilisation
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Example OS: SymbianOS
•Designed for mobile phones
• Gives access to
graphics, multimedia,
networking, telephony,
crypto,
PC connectivity, etc.
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The OS Wars
 Why is the OS such a big deal?
• Windows vs Linux vs Mac
• Symbian vs PalmOS vs Windows Mobile
 Incompatibilities
• OS’s have different interfaces.
• programs must be written differently.
• applications for one OS don’t run on
another.
 Tendency to bloatware
•
•
Applications tend to move into the OS
Internet Explorer, Media Player, Search?
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Security: Windows vs Linux
 Windows Family




Developed from DOS
Originally single-user machines
No network few threats
Linux



Developed from Unix
Originally multi-user networked servers
Designed to withstand with security threats
from the beginning
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THANK YOU
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