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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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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
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
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
USER View of OS
  • Ease to use (Home PCs)
  • Efficient resource utilization

(Work stations)

system view of os
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
1.2 Computer System Organization
  • Basic Organization
  • Storage Structure
  • I/O structure
computer startup
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 organization1
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.
1 2 2 storage structure
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 structure1
1.2.2 Storage Structure
  • Therefore, most computer provide secondary storage as extension to store web browser, compliers, word processors…etc
1 2 2 storage structure2
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.
  • 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 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
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
1.3.2 Multiprocessor Systems
  • Also called Parallel Systems
  • Advantages:
  • Increase throughput
  • Economy of scale
  • Increase reliability (fault tolerant)
1 3 2 multiprocessor systems1
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
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
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
  • Jobs are stored in “Job Pool”
  • Virtual memory is the useful technique for the limitation size of physical memory
1 5 os operations
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
  • 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.
c library handling of write
C library handling of write()


Int main()


printf(“hellow world”);


User mode

Standard C library

Kernel mode

Write() system call

dual mode operation1
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
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 management1
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 management2
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
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
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
Storage Management

OS provides uniform, logical view of information storage

  • file
  • Each medium is controlled by device (i.e., disk drive, tape drive)
storage management1
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
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 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 security1
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
Computing Environments

Traditional computer

  • Used to be single system, then modems
  • Now firewalled, networked
client server computing
Client-Server computing
  • Many system now servers, responding request to clients
peer peer to to peer computing
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-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
Operating System Services
  • User interface
  • Program execution
  • File-system manipulation
  • Communication
  • Error detection
  • Resource allocation
  • Accounting
  • Protection and security