Chapter 1 introduction to operating system
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Chapter 1 Introduction to Operating System. Bernard Chen Spring 2007. Outline. 1.1 What is OS 1.2 Computer System Organization 1.3 Computer System Architecture 1.4 OS Structure 1.5 OS Operations 1.6-1.8 Process, Memory, Storage management 1.9 Protection and Security 1.10~ Systems.

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Chapter 1 Introduction to Operating System

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Chapter 1Introduction to Operating System

Bernard Chen

Spring 2007


1.1 What is OS

1.2 Computer System Organization

1.3 Computer System Architecture

1.4 OS Structure

1.5 OS Operations

1.6-1.8 Process, Memory, Storage management

1.9 Protection and Security

1.10~ Systems

1.1 What is Operating System?

  • An operating system is a program that manages the computer hardware.

  • It also provides a basis for application programs and acts as an intermediary between the computer user and computer hardware.

What do Operating System do?

  • The computer system can be divided roughly into four components:

  • The hardware

  • The operating system

  • The application software

  • The Users

USER View of OS

  • Ease to use (Home PCs)

  • Efficient resource utilization

    (Work stations)

SYSTEM view of OS

  • OS is a resource allocator

    Manages all resources (CPU time, memory

    space, storage space, I/O and so on)

    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

1.2 Computer System Organization

  • Basic Organization

  • Storage Structure

  • I/O structure

Computer Startup

Bootstrap program is loaded at power up or reboot

  • Typically stored in ROM, generally known as firmware

  • Initialize all aspects of system

  • Loads operating system kernel and starts execution

1.2.1 Computer System Organization

1.2.1 Computer System Organization

  • I/O devices and the CPU can execute concurrently.

  • Each device controller is in charge of a particular device type.

  • Each device controller has a local buffer.

Interrupt Timeline

1.2.2 Storage Structure

Main Memory:

  • Main memory is the only large storage media that the CPU can access directly

  • Main memory is usually too small to store all needed programs and data

  • Main memory is a volatile storage device that loses its contents when power is off

1.2.2 Storage Structure

  • Therefore, most computer provide secondary storage as extension to store web browser, compliers, word processors…etc

Storage Device Hierarchy

1.2.2 Storage Structure

  • Storage systems organized in hierarchy.




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

Performance of Various Levels of Storage


  • Information in use copied from slower to faster storage temporarily

  • Important principle, performed at many levels in a computer (in hardware, operating system, software)


  • Faster storage (cache) checked first to determine if information is there

    If it is, information used directly from the cache (fast)

    If not, data copied to cache and used there

  • Cache is usually smaller than storage being cached

  • Cache management is an important design problem

  • Cache size and replacement policy

1.3 Computer-System Architecture

  • 1.3.1 Single-Processor Systems

  • 1.3.2 Multiprocessor Systems

  • 1.3.3 Cluster Systems

1.3.1 Single-Processor Systems

  • On a single processor system, there is only one main CPU capable of executing a general purpose instruction set.

  • Some other special-purpose processors may also included. Such as:


    Disk-controller microprocessor

    Keyboard microprocessor

1.3.2 Multiprocessor Systems

  • Also called Parallel Systems

  • Advantages:

  • Increase throughput

  • Economy of scale

  • Increase reliability (fault tolerant)

1.3.2 Multiprocessor Systems

  • Two types of multiprocessor systems:

    1. Asymmetric multiprocessing

    (master and slave processors)

    2. Symmetric multiprocessing

    (Shared memory system)

1.3.3 Clustered Systems

  • Clustered computers share storage and are closely linked via Local-area network (LAN) or a faster interconnection.

1.4 OS Architecture

One of the most important aspect of OS is the ability to Multiprogramming

  • Single user cannot keep CPU and I/O devices busy at all times

  • One job selected and run via job scheduling

  • When it has to wait (for I/O for example), OS switches to another job

Memory Layout for Multiprogrammed System


  • Jobs are stored in “Job Pool”

  • Virtual memory is the useful technique for the limitation size of physical memory

1.5 OS operations

  • Interrupt (driven by hardware) vs.

    Trap (called by software or error)

  • Trap example: divide by 0; invalid memory access

  • We need to make sure that an error in a user program could cause problems only for the one program that was running (such as infinite loop)

Dual Mode Operation

  • Dual-mode operation allows OS to protect itself and other system components

  • It contains user mode (mode bit:1) and Kernel mode (mode bit:0)

  • The operating system loaded user application starts in user mode. Whenever a trap or interrupt occurs, hardware switches to kernel mode.

Transition from user to kernel mode

C library handling of write()


Int main()


printf(“hellow world”);


User mode

Standard C library

Kernel mode

Write() system call

Dual Mode Operation

  • Privileged instructions: some machine instructions that may cause harm, can only be executed in kernel mode.

  • Such as instruction switch to user mode; I/O control; timer management, and interrupt management.


To prevent the OS out of control by CPU

  • Set interrupt after specific period

  • Operating system decrements counter

  • When counter zero generate an interrupt

  • Set up before scheduling process to regain control or terminate program that exceeds allotted time

Process management

  • A process is a program in execution. It is a unit of work within the system.

  • Process needs resources to accomplish its task CPU, Memory, files, I/O devices

  • Process termination requires reclaim of any reusable resources

Process management

  • Single-threaded process has one program counter (PC) specifying location of next instruction to execute

    Process executes instructions sequentially, one at a time until completion

  • Multi-threaded process has one program counter per thread

Process management

The operating system is responsible for the following activities in connection with process management:

  • Creating and deleting both user and system processes (Ch3)

  • Suspending and resuming processes (Ch5)

  • Providing mechanisms for process synchronization (Ch6)

  • Providing mechanisms for process communication (Ch4)

  • Providing mechanisms for deadlock handling(ch7)

Memory Management

  • All data in memory before and after processing

  • All instructions in memory in order to execute

  • Memory management determines what is in memory when optimizing CPU utilization and computer response to users

Memory management activities

  • Keeping track of which parts of memory are currently being used and by whom

  • Deciding which processes and data to move into and out of memory

  • Allocating and deallocating memory space as needed

Storage Management

OS provides uniform, logical view of information storage

  • file

  • Each medium is controlled by device (i.e., disk drive, tape drive)

Storage Management

File-System management

  • Files usually organized into directories

  • Access control on most systems to determine who can access what

  • OS activities include

  • Creating and deleting files and directories

  • Primitives to manipulate files and dirs

  • Mapping files onto secondary storage

  • Backup files onto stable (non-volatile) storage media

Mass Mass-Storage Management

  • Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time.

  • OS activities

  • Free-space management

  • Storage allocation

  • Disk scheduling

  • Tertiary storage includes optical storage, magnetic tape

  • Varies between WORM (write-once, read-many-times) and RW (read-write)

Protection and Security

  • Protection–any mechanism for controlling access of processes or users to resources defined by the OS (Ch14)

  • Security–defense of the system against internal and external attacks even when protection is activated (Ch15)

    (including denial-of-service, worms, viruses, identity theft, theft of service)

Protection and Security

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

  • Used to be single system, then modems

  • Now firewalled, networked

Client-Server computing

  • Many system now servers, responding request to clients

Peer Peer-to 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

Web-Based computing

  • Web has become ubiquitous

  • More devices becoming networked to allow web access, such as work stations, PDA, even cell phone

Operating System Services

  • User interface

  • Program execution

  • File-system manipulation

  • Communication

  • Error detection

  • Resource allocation

  • Accounting

  • Protection and security

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