CS212: OPERATING SYSTEM

Lecture 1: Introduction

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Chapter 1: Introduction What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Distributed Systems Computing Environments

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Objectives To provide a grand tour of the major operating systems

components To provide coverage of basic computer system organization

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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

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Computer System Structure Computer system can be divided into four components

Hardware – provides basic computing resources CPU, memory, I/O devices

Operating system Controls and coordinates use of hardware among

various applications and users Application programs – define the ways in which the

system resources are used to solve the computing problems of the users Word processors, compilers, web browsers, database

systems, video games Users

People, machines, other computers

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Four Components of a Computer System

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The operating system’s Role User View:

Single User (personal computer) OS designed for ease of use , with some attention paid to

performance. Multiple User’s (mainframe or minicomputer)

OS designed to maximize resource utilization. Workstations users connected to networks of other

workstations and servers OS designed to compromise between individual usability and

resource utilization.

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The operating system’s Role (cont.)

System View: OS is a resource allocator

Manages all resources Decides between conflicting requests for efficient and

fair resource use It is important when many users access the same

mainframe or minicomputer OS is a control program

Controls execution of programs to prevent errors and improper use of the computer

It is especially concerned with the operation and control of I/O devices.

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Operating System Definition

No universally accepted definition “The one program running at all times on the computer” is the

kernel. Everything else is either a system program (ships with the operating system) or an application program.

An operating system is a software that manages the computer hardware, as well as providing an

environment for application programs to run.

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Computer-System Organization Computer-System Operation Storage Structure I/O Structure

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Computer System operation Computer-system operation

One or more CPUs, device controllers connect through common bus providing access to shared memory

Concurrent execution of CPUs and devices competing for memory cycles

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Computer System Operation (cont.)Computer Startup: bootstrap program is loaded at power-up or reboot

Typically stored in ROM or EEPROM, generally known as firmware

Initializes all aspects of system Loads operating system kernel and starts execution

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Computer System Operation (cont.)Interrupt: The occurrence of an event is usually signaled by an

interrupt from either the hardware or the software. Hardware interrupts by sending a signal to the CPU through

system bus. Software interrupts by executing a special operation called a

system call.The interrupt is signal that gets the attention of the CPU and is usually generated when I/O is required. For example, hardware interrupts are generated when a key is pressed or when the mouse is moved. Software interrupts are generated by a program requiring disk input or output.

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Storage Hierarchy Storage systems organized in hierarchy

Speed Cost Volatility

Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage

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Storage-Device Hierarchy

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I/O Structure each device controller is in charge of a specific type of

device. A device controller maintains some local buffer storage

and a set of special-purpose registers. OS have a device driver for each device controller.

This device driver understands the device controller and presents a uniform interface to device to the rest of the operating system.

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Computer-System Architecture Multiprocessors systems growing in use and importance

Also known as parallel systems, tightly-coupled systems Advantages include

1. Increased throughput2. Economy of scale3. Increased reliability – fault tolerance

Two types1. Asymmetric Multiprocessing (master-slave relationship)2. Symmetric Multiprocessing (all processors are peers)

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Symmetric Multiprocessing Architecture

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A Dual-Core Design• Processors were originally developed with only one core. • The core is the part of the processor that actually performs the reading and executing of the instruction. Single-core processors can only process one instruction at a time• Dual-core processor contains two cores (Such as Intel Core Duo).

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Operating System Structure

Multiprogramming needed for efficiency Multiprogramming organizes jobs (code and data) so CPU

always has one to execute. (Increase CPU Utilization.) 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 jobMultiprogramming systems provide an environment inwhich the various system resources are utilized effectively,Not for user interaction with the computer system

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Memory Layout for Multiprogrammed System

Uniprogramming Processor must wait for I/O

instruction to complete before preceding

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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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Utilization Histograms

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Example

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Operating System Structure (cont.)

Timesharing (multitasking) is logical extension of multiprogramming 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

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Time Sharing Using multiprogramming to handle

multiple interactive jobs Processor’s time is shared among

multiple users Multiple users simultaneously access the

system through terminals

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Operating-System Operations 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

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Transition from User to Kernel Mode

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Distributed Systems Distributed systems allow users to share resources on

geographically dispersed hosts connected via a computer network.

The basic types of networks are: Local-area Network (LAN) connects computers within a room, a

floor, or a building. Wide-area Network (WAN) links building, cities or countries.

A network operating system provides features such as file sharing across the network and includes a communication scheme that allows different

processes on different computers to exchange messages

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Computing Environments Traditional computing (Centralized computing)

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, networkedCentralized computing is computing done at a central

location, using terminals that are attached to a central computer.

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Computing Environments (Cont)

Client-Server Computing 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

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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 To participate in a P2P system, a node must join P2P network

by: Registers its service with centralized lookup service on

network, or Broadcast request for service and respond to requests for

service via discovery protocol

Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition,

End of Chapter 1