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

Chapter 2: Operating-System Structures

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Last week Topics

What Operating Systems Do?

Distributed /Clustered Systems

Special-Purpose Systems

Open-Source Operating Systems

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Operating System News

Student 1

Student 2

Student 3

Share LatestOS news in 1 to 5minutes

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Chapter 2: Operating-System Structures

Operating System Services

User Operating System Interface

System Programs

Operating System Design and Implementation

Virtual Machines

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Bit , Byte and Word

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Machine cycle

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Virtual Memory

http://www.youtube.com/watch?v=Fx_I6-dL__0

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A View of Operating System Services

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Bourne Shell Command Interpreter

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The Mac OS X GUI

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API – System Call – OS Relationship

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Standard C Library Example

C program invoking printf() library call, which calls write() system call

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Types of System Calls

Process control

File management

Device management

Information maintenance

Communications

Protection

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Examples of Windows and Unix System Calls

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MS-DOS execution

(a) At system startup (b) running a program

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FreeBSD Running Multiple Programs

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MS-DOS Layer Structure

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Layered Approach

The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

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Traditional UNIX System Structure

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UNIX

UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts

Systems programs

The kernel

Consists of everything below the system-call interface and above the physical hardware

Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level

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Layered Operating System

Inner circleIs more protectedThan outer circle

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Microkernel System Structure Moves as much from the kernel into “user” space

Communication takes place between user modules using message passing

Benefits:

Easier to extend a microkernel

Easier to port the operating system to new architectures

More reliable (less code is running in kernel mode)

More secure

Detriments:

Performance overhead of user space to kernel space communication

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Why do we need Virtual Machine?

http://www.youtube.com/watch?v=V9AiN7oJaIM&feature=related

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Virtual Machines

A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware

A virtual machine provides an interface identical to the underlying bare hardware

The operating system host creates the illusion that a process has its own processor and (virtual memory)

Each guest provided with a (virtual) copy of underlying computer

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Virtual Machines (Cont)

(a) Nonvirtual machine (b) virtual machine

Non-virtual Machine Virtual Machine

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Linux : CLI (COMMAND LINE INTERFACE)

clear Clear screen

pwd Print Working Directory

cd Change Directory

mkdir Make Directory

rmdir Remove directory

ls List of directory

cp file1 file2 File2 would be created.

26

cd dir1 Change directory to dir1

cd / Change directory to root dir

cd Change Directory to home dir

cd ~ Change Directory to home dir

mv file1 file2 Rename file1 to file2

rm -f file2 Remove file file2

rm –I file2 Remove file in an interactive mode

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Linux: CLI (COMMAND LINE INTERFACE)

27 cat <<filename>> See the content of file

rm <<filename> Remove the file

mv <<oldfilename>> <<newfilename>> Rename the file

more <<filename>> View the file content, it allows scroll down

less <<filename>> View the file content, it allows scroll up and down

touch <<filename>> Empty file will be created

grep <<word>> filename

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

End of Chapter 2