Ch 2. Structure of OS

8/7/2019 Ch 2. Structure of OS

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07/06/2011

Chapter 2: Structure of OS


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Lecture 1

y Layered view of OS

y System Components

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Structure of Operating System:

Application Programs

System Programs

System Components(OS)

HARDWARE

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Layered Operating System

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Structure of Operating System (Contd)

y The structure of OS consists of 4 layers:

1. Hardware

Hardware consists of CPU,Main memory, I/ODevices, etc,

2. System Components(Operating System)

Software includes process management routines,memory management routines, I/O controlroutines, file management routines.

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Structure of Operating System (Contd)

3. System programs

This layer consists of compilers, Assemblers, linker

etc.

4. Application programs

This is dependent on users need.

E.g.Railway reservation system, Bank database

management etc.,

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System components......

PROCESS MANAGEMENTyA process is a program in execution: (A program is passive, a

process active.)E.g.Word processing program run by an user

yA process has resources (CPU time, files, memory) andattributes that must be managed.

yApart from resources, a process may require variousinitialization data.

E.g. User process compiler requires a file to compile &

appropriate system calls.y When the process terminates the OS will reclaim any

reusable resources.

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PROCESS MANAGEMENT

yManagement of processes includes:

y Process Scheduling (priority, time management, . . . )

y Creation/termination

y Block/Unblock (suspension/resumption )y Synchronization

y Communication

y Deadlock handling

y

Debugging

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MAIN MEMORY MANAGEMENT

For a program to be executed, it must be mapped to absolute addresses

and loaded into memory.

To improve both the utilization of the CPU and speed of the computers

response to its users, we must keep several programs in main memory.

Hence, proper memory management schemes are required.

Memory management activities by OS

yAllocation/de-allocation for processes, files, I/O.

yM

aintenance of several processes at a timeyKeep track of who's using what memory

yMovement of process memory to/from secondary storage.


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FILE MANAGEMENT

y A file is a collection of related information defined by its creator.

Commonly, files represent programs (both source and object

forms) and data.

y The operating system is responsible for t

he following activities inconnections with file management:

File creation and deletion.

Directory creation and deletion.

Support of primitives for manipulating files and directories. Mapping files onto secondary storage.

File backup on stable (nonvolatile) storage media.


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I/O MANAGEMENT

y Buffer caching system

yGeneric device driver code

y Drivers for each device - translate read/write requests intodisk position commands.

SECONDARY STORAGE MANAGEMENTy Disks, tapes, optical, ...

y Free space management ( paging/swapping )

y Storage allocation ( what data goes where on disk )

y Disk scheduling


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NETWORKING

y Communication system between distributed processors.

yGetting information about files/processes/etc. on a remote

machine.

y Can use either a message passing or a shared memory model.

PROTECTION

y Of files, memory, CPU, etc.

yM

eans controlling of accessy Depends on the attributes of the file and user


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SYSTEM PROGRAMS

y Command Interpreters -- Program that accepts control

statements (shell,GUI interface, etc.)

y Compilers/linkersy Communications (FTP,TELNET,etc)

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Lecture 2

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y Shell

y Kernel

y System calls

y System programsy Virtual machines

y Java virtual machines

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Shell or Command interpreter

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y

A shell is a piece of software that provides an interface forusers of an operating system which provides access to the

services of a kernel.


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y OS shells generally fall into one of two categories:- Command-line shells provide a command-line interface (CLI)

to the operating system.

E.g. Unix

- Graphical shells provide a graphical user interface (GUI)

E.g.Windows

Shell.


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Kernel

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y The kernel is the essential centre of a computer operating system,

the core that provides basic services for all other parts of the

operating system.

y A kernel includes,

- An interrupt handler that handles all requests or completed

I/O operations

- a scheduler that determines which programs share the kernel's

processing time in what order, and a supervisor that actually

gives use of the computer to each process when it is scheduled.-A kernel may also include a manager of the operating system's

address spaces in memory or storage, sharing these among all

components and other users of the kernel's services.


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System Calls

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y System calls provide interface between a process & the operatingsystem.

y System calls can be made either in assembly or high levellanguage.

y A collection of system calls is sometimes referred to as anapplication program interface (API).

y Three most common APIs are Win32API for Windows, POSIXAPI for POSIX-based systems (including virtually all versions of

UNIX, Linux, and Mac OS X), and Java API for the Java virtualmachine (JVM)


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System calls..

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Example of System Calls

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y System call sequence to copy the contents of one file to another file(Command line

interface)


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File copy example..

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y The file copy operation makesheavy use of OS (system

calls).

y Most users never see this level of details.

y The run time support system (set of libraries includedwith a compiler) for most programming languages

provides a much simpler interface.


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Example..

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C++ file copy program: filecopy.cpp

#include

#include

void main()

{

ifstream infile(D:input.txt);

ofstream outfile(D:output.txt);char ch;

//continue reading file until EOF is reached

while(infile){

infile.get(ch);outfile.put(ch);

}

}


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Standard Library functions Vs system calls

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y Standard library functions are built on top of system calls. For

example, the malloc() in C and related functions are built on

top of the mmap() system call(LINUX).This means that

greater control over the computers resources can be obtained

through system calls.

y Standard library functions tend to be more standardized than

system calls. since system calls provide direct access to the

kernel, different O/Ss will have at least slightly different

system calls.


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Passing parameters to operating system

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y 3 methods

1. Parameters in registers.

2. For more parameters, block of memory is used. Address

of the memory block where parameters are stored is

passed as parameter in a register. (LINUX)


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3. Parameters can be placed or pushed onto the stack by the

program and popped off the stack by the operating system.

y

Some operating systems prefer the block or stack met

hods,

because those approaches do not limit the number or length of

parameters being passed.

Passing parameters to operating system


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API System Call OS Relationship

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Standard C Library Example

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


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There are 11 (or more) steps in making the system call

read (fd, buffer, nbytes)

Linux system call


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Types of System Calls

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y Process control

y File management

y Device management

yInformation maintenance

y Communications


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System programs

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y

System programs provide a convenient environment for programdevelopment and execution.

y They are divided into these categories:

1. File management:These programs create, delete, copy, rename,

print, list and generally manipulate files and directories.


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System Programs

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2. Status information: Some programs simply ask the system for the

data, amount of available memory or disk space, number of users,

etc..

yThat information is then formatted and presented.

3. File Modification: Several text editors may be available to createand modify the content of files stored on the disk.

E.g.MS word, Notepad


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3. Programming language support: Compilers, assemblers and

interpreters for common programming languages are often

provided to user the OS.

4. Program loading and execution:The system may provide

absolute loaders, relocatable loaders, linkers, etc..

5.Communications :Th

ese programs allow users to send messagesto one anothers screens, to browse web pages, to send email ,

etc

E.g. Internet Explorer, windows mail

y Most important system program for an operating system iscommand interpreter or shell.

System Programs


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Simple Structure

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y MS-DOS written to provide the most functionality in the

least space

y Not divided into modules

y AlthoughMS-DOS has some structure, its interfaces and levels

of functionality are not well separated


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MS-DOS Layer Structure

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UNIX

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y UNIX limited by hardware functionality, the original

UNIX operating system had limited structuring. The UNIX

OS consists of two separable parts

y Systems programs

y The kernel

y Consists of everything below the system-call interface and above the

physical hardware

y 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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UNIX System Structure

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Microkernel System Structure

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y Moves as much from the kernel into user space

y Communication takes place between user modules usingmessage passing

y Benefits:y Easier to extend a microkernel

y Easier to port the operating system to new architectures

y More reliable (less code is running in kernel mode)

y More secure

y Detriments:y Performance overhead of user space to kernel space

communication


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Virtual Machines

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y In a Virtual Machine - each process "seems" to execute on its

own processor with its own memory, devices, etc.

y A virtual machine provides an interface identicalto the

underlying bare hardware

y The operating system creates the illusion of multiple processes,

each executing on its own processor with its own (virtual)

memory


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Virtual Machines (Contd)

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y The resources of the physical computer are shared to create thevirtual machinesy CPU scheduling can create the appearance that users have their

own processor

y Spooling and a file system can provide virtual card readers andvirtual line printers

y A normal user time-sharing terminal serves as the virtual machineoperators console

y The virtual-mac

hine concept provides complete protection of systemresources since each virtual machine is isolated from all other virtual

machines. This isolation, however, permits no direct sharing ofresources.


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Virtual Machines (Cont.)

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(a) Nonvirtual machine (b) virtual machine

Non-virtualM

ach

ine VirtualM

achine


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JVM

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Verifier


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JVM

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The class loaderloads .class files from both the Java program

and Java API for execution by the Java interpreter.

The verifierchecks the class file is valid Java bytecode and

does not overflow or underflow the stack.

The JVMinterpreterthat interprets the bytecodes one at a time

to turn the architecture neutral bytecodes into native

machine language of the host computer.

The JVMmakes it possible to develop programs that are

architecture neutral and portable.

The implementation of the JVM is specific for each system.

Ch 2. Structure of OS

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