Chapter 1Introduction to Operating System

Bernard ChenSpring 2007

Outline

1.1 What is OS1.2 Computer System Organization1.3 Computer System Architecture1.4 OS Structure1.5 OS Operations 1.6-1.8 Process, Memory, Storage

management1.9 Protection and Security1.10~ 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:

1. The hardware2. The operating system3. The application software4. 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. Speed Cost Volatility 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

Caching

Information in use copied from slower to faster storage temporarily

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

Caching 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:

GPU Disk-controller microprocessor Keyboard microprocessor

1.3.2 Multiprocessor Systems

Also called Parallel Systems

Advantages:1. Increase throughput 2. Economy of scale3. 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

Multiprogramming

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()

#include<stdio.h>

Int main()

{

…

printf(“hellow world”);

…

}

Standard C libraryUser mode

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.

Timer

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 include1. Creating and deleting files and directories2. Primitives to manipulate files and dirs3. Mapping files onto secondary storage4. 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 activities1. Free-space management2. Storage allocation3. Disk scheduling4. Tertiary storage includes optical storage,

magnetic tape5. 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

1. Instead all nodes are considered peers2. May each act as client, server or both3. 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