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Operating System Structures

System Components

Operating System Services

System Calls

System Programs

System Structures

Virtual Machines

System Design and Implementation

System Generation

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System Components

Process Management

MainMemory Management

File Management

I/O System Management

Secondary Storage / Disk Management

Networking

Protection System

Command Interpreter System

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System Components

ProcessProgram in execution.

Active entity.

Unit work in a system.

Ex: Time-shared user program

Word-processing program

System task

Sending output to printer.

Needs certain resources.CPU time

Memory

Files

I/O devices

Types

System processes (execute system code).

User processes (execute user code).

Program CounterSpecifies the next instruction to execute.

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System Components

Process Management

Activitiesy Create and delete both user and system processes.

y Suspend and resume processes.

y Provide mechanisms for process synchronisation.

y Provide mechanisms for process communication.

y Provide mechanisms for deadlock handling.

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System Components

MainMemory Management

Activitiesy Keep track of which parts of memory are currently being used and

by whom.

y Decide which processes are to be loaded into memory when memory

space becomes available.

y Allocate and deallocate memory space as needed.

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System Components

File

Collection of related information.

Represents programs and data.

Consists of sequence of bits, bytes, lines or records.

Organised into directories to ease their use.

Types

Free-form (Text files)

Fixed-form

Data files

Numeric

Alphabetic

Alphanumeric

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System Components

File ManagementOne of the most visible components of operating system.

Activitiesy Create and delete files.

y Create and delete directories.

y Support primitives for manipulating files and directories.

y Map files onto secondary storage.

y Back up files on stable (nonvolatile) storage media.

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System Components

I/O System Managementy

Memory management components.Buffering

Caching

spooling

y General device driver interface.

y Drivers for specific hardware devices.

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System Components

Secondary Storage / Disk Management

Activitiesy Free space management

y Storage allocation

y Disk scheduling

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System Components

Networking

Distributed System

Collection of processors

do not share

MemoryPeripheral devices

Clock.

Collects physically separate heterogeneous systems into single

coherent system.

Provides the user with access to various resources system maintains.

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System Components

Protection System

Mechanism for controlling access of programs, processes or users tothe resources.

Improve reliability.

Command Interpreter SystemInterface between user and OS.

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Operating System ServicesOS provides no. of services.

Lowest level System calls

Allow running program to make requests from the OS directly.Higher level Command interpreter or Shell

User issues request without writing program.

Categories

Program Control

Status requestsI/O requests

Program execution

I/O operations

File system manipulation

CommunicationsError detection

Resource allocation

Accounting

Protection

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Program execution

System must be able toload program into memory.

run that program.

Programs must be able to end its execution, either normally or

abnormally (indicating error).

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I/O operations

OS must provide means to do I/O.

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File system manipulation

Programs need to read and write files.

Programs also need to create and delete files by name.

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Communications

One process needs to exchange information with another process.

Implemented via shared memory or message passing technique.

Message passingPackets of information moved between processes by OS.

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Error detection

Resource allocation

AccountingRecord keeping may be used.

ProtectionEnsures that all access to system resources is controlled.

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System Calls

Provide interface between process and OS.

Major categories

Process control

File management

Device management

Information maintenance

Communications

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System Calls

Process controly

End, abort

y Load, execute

y Create process, terminate process

y Get process attributes, set process attributes

y Wait for time

y Wait event, signal event

y Allocate and free memory

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System Calls

File managementy Create file, delete file

y Open, close

y Read, write, reposition

y Get file attributes, set file attributes

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System Calls

Device managementy Request device, release device

y Read, write, reposition

y Get device attributes, set device attributes

y Logically attach or detach devices

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System Calls

Information maintenancey Get time or date, set time or date

y Get system data, set system data

y Get process, file, or device attributes

y Set process, file, or device attributes

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System Calls

Communicationsy Create, delete communication connection

y Send, receive messages

y Transfer status information

y Attach or detach remote devices

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System Programs

Provide convenient environment for program development and execution.

Categories

File management

Status information

File modification

Programming language support

Program loading and executionCommunications

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System Programs

File managementCreate

Delete

Copy

Rename

Print

Dump

ListManipulate files and directories.

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System Programs

Status informationDate

Time

Amount of available memory / disk space

No. of users

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System Programs

File modification

Text editors

To create and modify the content of files stored on disk or tape.

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System Programs

Programming language supportCompilers

Assemblers

Interpreters

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System Programs

Program loading and executionAbsolute loaders

Relocatable loaders

Linkage editors

Overlay loaders

Debugging systems

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System Programs

CommunicationsProvide mechanism for creating virtual connections among

processes, users and different computer systems.

Allow users to

Send messages to one anothers screens.

Browse web pages.

Send electronic mail messages.Log in remotely.

Transfer files from one machine to another.

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System Structures

Partition the task into small components.

Types

Simple Structure

Layered Approach

Microkernels

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System Structures

MS-DOS Layer Structure

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System Structures

UNIX System Structure

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System Structures

Layered ApproachOperating system broken up into no. of layers (levels).

Each built on lower layers.

Bottom layer (layer 0) Hardware

Highest layer (layer N) User interface

Main advantageModularity

Simplified design and implementation of the system.

Each layer is implemented only by the lower layer operations.

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System Structures

Layered Approach

Operating System LayerSreedhar Potla

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System Structures

Microkernel approachStructures OS by removing all nonessential components from the

kernel.

Implements nonessential components as system-level and user-level

programs.

Typically provides minimal process and memory management.

Main function

Provides communication facility (message passing) betweenthe client program and the various services running in user

space.

Benefits

Ease of extending OS.

Provides more security and reliability.

Examples

Tru64 UNIX

QNX (RTOS)

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Virtual Machines

Provides interface.

Each process is provided with (virtual) copy of the underlying computer.

Major difficulty

Cannot allocate disk drive to each virtual machine.

Provides virtual disks (minidisks).

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Virtual Machines

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Virtual Machines

ImplementationDifficult to implement.

Modes

Virtual user mode.

Virtual monitor mode.

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Virtual Machines

BenefitsProvides robust level of security.

Allows system development.

Each virtual machine is completely isolated from all other virtual

machines.

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Virtual Machines

JavaVery popular object oriented language.

Introduced by Sun Microsystems in late 1995.

Provides specification for Java Virtual Machine (JVM).

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Virtual Machines

Java Virtual Machine (JVM)

Automatically manages memory by performing garbage collection.

Its design provides

Secure

Efficient

Object oriented

PortableArchitecture-neutral platform.

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Virtual Machines


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Virtual Machines

Java Virtual Machine (JVM)Consists of

Class loader

Class verifier

Java interpreter

Class loader

Loads .class files.

Class verifier

Checks

the class file is valid Java bytecode.

Does not overflow or underflow the stack.

Also ensures that the bytecode does not perform pointer arithmetic.

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Virtual Machines


Java interpreter

Interprets bytecodes one at a time.

Just-in-time (JIT) compiler.

Just-in-time (JIT) compilerTurns the architecture neutral bytecodes into native machine

language for the host computer

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Design Goals

Mechanisms and Policies

Implementation

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Design Goals

Define the goals and specifications of the system.

User goalsSystem should be

convenient and easy to use

easy to learn

reliable

safe

fast.System goals

OS should be

Easy to design

Implement

MaintainFlexible

Reliable

Error free

Efficient.

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Mechanisms and Policies

Mechanisms

Determine how to do something.

Ex: Timer construct (Mechanism for ensuring CPU protection)

PoliciesDetermine what will be done.

Ex: How long the time is to be set for a particular user?

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ImplementationMaster Control Program (MCP)

Burroughs Computers.

Written in variant of ALGOL.

MULTiplex Information and Computing Service (MULTICS)

Developed at MIT.

Written in PL/1.

Primos

Prime computers.

Written in dialect of FORTRAN.

UNIX, OS/2, Windows NT

Mainly written in C.

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System Generation (SYSGEN)

obtains information concerning the specific configuration of thehardware system.

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OS-03

Documents

Transcript of OS-03