Unit 1 introduction to Operating System

Introduction to Operating System
S.R INAMDAR1Dept. of CSE BLDEA'S SSM POLYTECHNIC

Chapter 1: Introduction
 What Operating Systems Do
 Computer-System Architecture
 Operating-System Structure
 Operating-System Operations
 Process Management
 Memory Management
 Storage Management
 Protection and Security
 Distributed Systems
 Special-Purpose Systems
 Computing Environments
 Open-source Operating Systems.
2Dept. of CSE BLDEA'S SSM POLYTECHNIC

What is an Operating System?
 A program that acts as an intermediary between a user of a
computer and the computer hardware.
 Operating system goals:
 Execute user programs and make solving user problems
easier.
 Make the computer system convenient to use.
 Use the computer hardware in an efficient manner.

Operating System Definition
 OS is a resource allocator
 Manages all resources
 Decides between conflicting requests for efficient and fair
resource use
 OS is a control program
 Controls execution of programs to prevent errors and
improper use of the computer

Operating System Structure
Multiprogramming needed for efficiency
 Single user cannot keep CPU and I/O devices busy at all times
 Multiprogramming organizes jobs (code and data) so CPU
always has one to execute
 A subset of total jobs in system is kept in memory
 One job selected and run via job scheduling
 When it has to wait (for I/O for example), OS switches to
another job

Operating System Structure (cont.)
 Timesharing (multitasking) is logical extension in which CPU switches
jobs so frequently that users can interact with each job while it is
running, creating interactive computing
 Response time should be < 1 second
 Each user has at least one program executing in memory process
 If several jobs ready to run at the same time  CPU scheduling
 If processes don’t fit in memory, swapping moves them in and out to run
 Virtual memory allows execution of processes not completely in
memory

Operating-System Operations
 Interrupt driven by hardware
 Software error or request creates exception or trap
 Division by zero, request for operating system service
 Other process problems include infinite loop, processes
modifying each other or the operating system

Operating-System Operations (Cont.)
 Dual-mode operation allows OS to protect itself and other system
components
 User mode and kernel mode
 Mode bit provided by hardware
 Provides ability to distinguish when system is running user
code or kernel code
 Some instructions designated as privileged, only executable in
kernel mode
 System call changes mode to kernel, return from call resets it to
user

Process Management Activities
The operating system is responsible for the following
activities in connection with process management:
 Creating and deleting both user and system processes
 Suspending and resuming processes
 Providing mechanisms for process synchronization
 Providing mechanisms for process communication
 Providing mechanisms for deadlock handling

Memory Management
 Memory management activities
 Keeping track of which parts of memory are currently being
used and by whom
 Deciding which processes (or parts thereof) and data to
move into and out of memory
 Allocating and deallocating memory space as needed

Storage Management
 OS activities include
 Creating and deleting files and directories
 Primitives to manipulate files and disc
 Mapping files onto secondary storage
 Backup files onto stable (non-volatile) storage media

Mass-Storage Management
 OS activities
 Free-space management
 Storage allocation
 Disk scheduling

Protection and Security
 Protection – any mechanism for controlling access of processes or users to
resources defined by the OS
 Security – defense of the system against internal and external attacks
 Huge range, including denial-of-service, worms, viruses, identity theft, theft of
service
 Systems generally first distinguish among users, to determine who can do what
 User identities (user IDs, security IDs) include name and associated number, one per
user
 User ID then associated with all files, processes of that user to determine access
control
 Group identifier (group ID) allows set of users to be defined and controls managed,
then also associated with each process, file
 Privilege escalation allows user to change to effective ID with more rights

Computing Environments
 Traditional computer
 Blurring over time
 Office environment
 PCs connected to a network, terminals attached to mainframe or
minicomputers providing batch and timesharing
 Now portals allowing networked and remote systems access to same
resources
 Home networks
 Used to be single system, then modems
 Now firewalled, networked

Client-Server Computing
 Dumb terminals supplanted by smart PCs
 Many systems now servers, responding to requests generated by
clients
 Compute-server provides an interface to client to request services
(i.e. database)
 File-server provides interface for clients to store and retrieve files

Peer-to-Peer Computing
 Another model of distributed system
 P2P does not distinguish clients and servers
 Instead all nodes are considered peers
 May each act as client, server or both
 Node must join P2P network
 Registers its service with central lookup service on network, or
 Broadcast request for service and respond to requests for service
via discovery protocol
 Examples include Napster and Gnutella

Web-Based Computing
 Web has become ubiquitous
 PCs most prevalent devices
 More devices becoming networked to allow web access
 New category of devices to manage web traffic among
similar servers: load balancers
 Use of operating systems like Windows 95, client-side,
have evolved into Linux and Windows XP, which can be
clients and servers

THANK YOU

Unit 1 introduction to Operating System

More Related Content

What's hot (20)

Similar to Unit 1 introduction to Operating System (20)

More from zahid7578 (7)

Recently uploaded (20)

Unit 1 introduction to Operating System