Operating System Concepts Part II Department of Computer Science Southern Illinois University...

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Operating System Concepts Part II

Department of Computer ScienceSouthern Illinois University Edwardsville

Spring, 2009

Dr. Hiroshi FujinokiE-mail: hfujino@siue.edu

CS 514 Operating Systems

Intro_II/001

Operating System Concepts

This PPT presentation covers Section 1.5 of the textbook.

(1) Process

(2) Deadlock avoidance in I/O resource management

(3) Files and file descriptor

(4) Special Files

Intro_II/002

Subjects covered about “process”

• What is “process”?

• How is it different from “program”?

• What we can do by “processes”?

A: “Process” is a program in execution.

“program” is an executablefile stored in a disk

program

Stored as a file

Q: What is “process”?

Solutions

Intro_II/003

Then how a “program” can become “process”?

program

Stored as a file

Memory

A program becomes a process

when one is loaded into the memory for execution by CPU

Intro_II/004

Things needed for a program to be executed in memory

Memory

Program Code

Stack Memory

Heap Memory

AddressSpace

Program X

Program Z

PCB-Z PCB-A PCB-X

PCB = Process Control Block

PCB is a data structure for the CPUto keep track of each process

Process

Program

Intro_II/005

Example of “program” and “process”

• Program

• Process

Static object, usually exists as an executable file

Program in execution

This is a program

This is a process (program in execution)

Intro_II/006

Intermediate summary of “process”

• It is a program in execution

• A process consists of the contents in process address space and PCB

• Process address space consists of:

Program Code

Stack Memory Space

Heap Memory Space

Collection of assembly instructions CPU runs

Stack data structure for sub-routine calls

Other data structure (local/global variables)

Questions

Where are PCBs located?

What information does PCB hold?

Intro_II/007

Things needed for a program to be executed in memory

Memory

Program X

Program Z

PCB-Z PCB-A PCB-X

Program Y

Where are PCBs located?

In the operating system

Intro_II/008

Deadlock

Deadlock avoidance in I/O resource management

What is “deadlock”?

More than one process wait for resource for each other for forever

Example

Resources

Printer

• Assume that there are two processes• Each of the two processes requires printer and HDD at the same time

• Without the printer and HDD, neither can finish its tasks

Process AProcess B

Assigned

Assignedwait

(Circular-wait)

Intro_II/009

Concept of files and file descriptor

Logical data storages in computer systems

What is a file?

What is “file descriptor”?

Logical identification for each file being usedin a computer system.

open read

Intro_II/010

Concept of files and file descriptor (continued)

File Names

“A.txt”

Location on disk

• Sectors• Track• Platters

Open “A.txt”

Find/Access

LoadFile Descriptor

• Read (FD)• Write (FD)• Append (FD)

File Names Sector Locations

File Allocation Table

A.txt 1E23CD

Intro_II/011

Concept of Special Files

Ordinary File

Can not be seenby human user

Special Files

Keyboard

printer

Users can I/O tomany devices as if they

were a file

ModemInternet

Request

Request (1)

Response (4)Internet

Request

Network

Special Files

Intro_II/012

Special Files

A concept in OS where a user can handle many I/O devicesusing the same interface (APIs) that is used for actual files.

• When you open (reserve) a resource, OS gives you “descriptor”

• Some special files are read-only and some others may be write-only

Read-OnlyRead/Write Write-Only

- Disks - Keyboard - Printer

- Network - Mouse

- CRT Monitor (with touch-pen support)

- CD-ROM

- CRT Monitor

Intro_II/013

Operating System Structure

Monolithic Structure

Layered Structure

VM (Virtual Machine)

Micro-KernelWindows uses these concepts

This PPT presentation covers Section 1.7 of the textbook.

Intro_II/014

Monolithic Structure OS

• Operating systems are essentially a collection of procedures.

Monolithic Structure OS No structure in a collection of procedures

(Any procedure or a user application can call any other procedure)

OS Procedures

Disk I/O

Process Mgmt.

Memory Mgmt.

Printer Spooler

KB I/O

Program

• Big mess

• But fast (no overhead)

Intro_II/015

How is a Monolithic-Structured OS implemented?

OS Procedures

Disk I/O

Process Mgmt.

Memory Mgmt.

Printer Spooler

IPCKB I/O

Disk I/O

Memory Mgmt.

Process Mgmt.

KB I/O

Printer Spooler

Source codemodules

Concatenate intoone source code file

Compile

Operating system as an executable program

Intro_II/016

“OS” in a broader definition

How is a Monolithic-Structured OS implemented?

Operating system as an executable program

Disk I/O

Memory Mgmt.

Process Mgmt.

KB I/O

Printer Spooler

Program

System calls

External Commands

execute

exec ();

“OS Kernel”

Intro_II/017

Layered Structure Operating Systems

“Layers” Layers of priorities

User Programs

I/O Management

Process Communication

Memory Management

Process Management

Intro_II/018

Virtual Machine (VM)

Without VM

Hardware

Operating System

App1 App N

Virtual Machine Support

OS2 OS3

A virtual machine

UNIXWindows 2000

Application programs

Hardware

With VM

MS-DOS

Extra layer ontop of hardware

Intro_II/019

Hardware

OS2 OS3

Hardware1

OS2 OS3

Hardware2 Hardware3

Concept of VM

For each application program,it looks like they are beingexecuted by the dedicated

hardware

Intro_II/020

Without VM

Memory

Process X

Process Y

Process Z

With VM

Memory

Process X

Process Y

ProcessManage

Process M

Process NProcessManage

Process A

Process BProcessManage

VMManage

Implementation of of VM

Intro_II/021

MS-DOS MS-DOS

Hardware

Windows-9x VM

• All Win-32 applications are execute in Win-32 kernel

• Each MS-DOS application will be executed within its VM

MS-DOS VMCS 514 Operating Systems

Intro_II/022

Summary of Virtual Machine (VM)

VM A virtual computer where computer hardware is software-emulatedby VMS (Virtual Machine Support)

• Provide virtual dedicated machine (= hardware) to each OS

Multiple operating systems (and its applications) at once

(Q: What’s the difference from “multiple boot”?)

- For flexibility

- For robustness

One VM crashes, others still survive

(EG: Windows-NT)

Intro_II/023

Disk I/O

Memory Mgmt.

Process Mgmt.

KB I/O

Printer Spooler

External Commands

“OS Kernel”

Micro-Kernel Architecture

Intro_II/024

Disk I/O

KB I/O

Memory Mgmt.

Process Mgmt.

Printer Spooler

External Commands

“OS Kernel”

Micro-Kernel Architecture (continued)

Memory Mgmt.

Process Mgmt.

Printer Spooler

Intro_II/025

Computer Hardware

Operating System

User Program

User-Mode

Kernel-Mode

In ordinary OS (not Micro-Kernel OS), OS has to provideall the user services in Kernel-mode services

OS kernel tends to be huge

System Call

OS Procedure (in the OS kernel)

Intro_II/026

Computer Hardware

Operating System

User Program

User-Mode

Kernel-Mode

Spooler

Micro-Kernel Architecture is based on Client-Server Model

Client Server

Micro-kernel Architecture Make the OS kernel as small as possible

Operating System becomes a service broker

Intro_II/027

What is it good for?

MS Windows uses micro-kernel architecture for this reason

(1) Each OS function becomes a module

A bug in OS can be fixed by replacing a module

(what we should do if “monolithic structure kernel”?)

(2) Better robustness

OS functions may be executed in user-mode

(a bug in a module will not crash the kernel)

Intro_II/028

Operating System Concepts Part II Department of Computer Science Southern Illinois University...

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