4_OS Structure..ppt

8/14/2019 4_OS Structure..ppt

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Operating-System Structures

1. Operating-System System Components

2. Operating System Services

3. System Calls4. System Structure

5. Virtual Machines

6. System Design and Implementation

7. System Generation


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1.Operating System Components

Process Management

Main Memory Management

File Management

I/O System Management Secondary Management

Networking

Protection System

Command-Interpreter System


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1. Process Management

Aprocessis a program in execution

A process needs certain resources,including CPU time, memory, files, andI/O devices, to accomplish its task

The operating system is responsible for the

following activities in connection withprocess management

Process creation and deletion

Process suspension and resumption

Provision of mechanisms for:

process synchronization

process communication


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Memoryis a large array of words or bytes, each with

its own address It is responsible for quickly accessible data

shared by the CPU and I/O devices

Main memoryis a volatile storage device. It loses its

contents in the case of system failure The operating system is responsible for the following

activities in connections with memory management

Keep track of which parts of memory are currently

being used and by whom Decide which processes to load when memory

space becomes available

Allocate and deallocate memory space as needed

2. Main-Memory Management


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A fileis a collection of related information defined

by its creator Commonly, files represent programs and data

The operating system is responsible for thefollowing activities in connections 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) storagemedia

3. File Management


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4. I/O System Management

The I/O system consists of:

A buffer-caching system

A general device-driver interface

Drivers for specific hardware devices


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Since main memory (primary storage) is volatile

and too small to accommodate all data andprograms permanently, the computer systemmust provide secondary storageto back up mainmemory

The operating system is responsible for the

following activities in connection with diskmanagement:

Free space management

Storage allocation

Disk scheduling

5. Secondary-Storage Management


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6. Networking (Distributed Systems)

A distributedsystem is a collection processorsthat do not share memory or a clock

Each processor has its own local memory

The processors in the system are connected

through a communication network Communication takes place using aprotocol

A distributed system provides user access tovarious system resources

Access to a shared resource allows: Computation speed-up

Increased data availability

Enhanced reliability


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7. Protection System

Protectionrefers to a mechanism for controllingaccess by programs, processes, or users to bothsystem and user resources

The protection mechanism must:

distinguish between authorizedandunauthorizedusage

specify the controls to be imposed

provide a means of enforcement


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8. Command-Interpreter System

Many commands are given to the operatingsystem by control statements which deal with:

Process creation and management

I/O handling Secondary-storage management

Main-memory management

File-system access

Protection Networking


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1. Program execution System capability toload a program into memory and to run it

2.

I/O operations Since user programscannot execute I/O operations directly,the operating system must provide somemeans to perform I/O

3. File-system manipulation Programcapability to read, write, create, anddelete files

3.System Calls

Operating System Services


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4. Communications Exchange of

information between processes executingeither on the same computer or ondifferent systems tied together by anetwork. Implemented via shared

memory or message passing

5. Error detection Ensure correctcomputing by detecting errors in the CPU

and memory hardware, in I/O devices, orin user programs


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Three general methods are used topassparametersbetween a running programand the operating system

Passparametersin registers Store the parameters in a table inmemory, and the table addressispassed as a parameter in a register

Push(store) the parameters onto thestackby the program, andpopoff thestack by operating system


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Passing of Parameters As A Table


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Types of System Calls

Process control

File management

Device management

Information maintenance Communications


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Communication Models

Message PassingShared Memory

Communication may take place using either

message passing or shared memory


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4. MS-DOS System Structure

MS-DOS written to provide the mostfunctionality in the least space

Not divided into modules

Although MS-DOS has some structure, itsinterfaces and levels of functionality are notwell separated


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MS-DOS Layer Structure


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Layered Approach

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

With modularity, layers are selected such thateach uses functions (operations) and services ofonly lower-level layers


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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 newarchitectures

More reliable (less code is running in kernel

mode)

More secure


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Windows NT Client-Server Structure


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5.Virtual Machines

A virtual machinetakes the layered approach toits logical conclusion. It treats hardware and theoperating system kernel as though they were allhardware

A virtual machine provides an interface identicalto the underlying bare hardware

The operating system creates the illusion ofmultiple processes, each executing on its own

processor with its own (virtual) memory


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Virtual Machines (Cont.)

The resources of the physical computer areshared to create the virtual machines

CPU scheduling can create the appearance thatusers have their own processor

Spooling and a file system can provide virtualcard readers and virtual line printers

A normal user time-sharing terminal serves asthe virtual machine operators console


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System Models

Non-virtual Machine Virtual Machine


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Advantages/Disadvantages of Virtual Machines

The virtual-machine concept provides completeprotection of system resources since each virtualmachine is isolated from all other virtualmachines. This isolation, however, permits no

direct sharing of resources. A virtual-machine system is a perfect vehicle for

operating-systems research and development.System development is done on the virtualmachine, instead of on a physical machine and sodoes not disrupt normal system operation.

The virtual machine concept is difficult toimplement due to the effort required to provide anexactduplicate to the underlying machine


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System Design Goals

User goals operating system should beconvenient to use, easy to learn, reliable, safe,

and fast System goals operating system should be easy

to design, implement, and maintain, as well asflexible, reliable, error-free, and efficient


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System Generation (SYSGEN)

Operating systems are designed to run on any ofa class of machines; the system must beconfigured for each specific computer site

SYSGEN program obtains information concerning

the specific configuration of the hardware system Bootingstarting a computer by loading the

kernel

Bootstrap programcode stored in ROM that is

able to locate the kernel, load it into memory,and start its execution


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