OS_LECT1&2

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OPERATING SYSTEM

Lecture-1 & 2

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Topics

Operating System

Functions of OS

Types of OS

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Operating System: Definition

It is the software layer, nearest to hardware which

facilitates launching of all the other software utilities

andapplications.

OS provides wide range ofgeneric data services.

Manages keyboard, display, processor, memory

andother devices.

Schedules input, output and data processing.

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User and OS

OS facilitates use of resources by hiding local

details and presenting an interface which is

convenient to use.

For instance : computer games, e-mail, browsing

or preparing documents are applications launched

by simply clicking on cue icons. How easy it is !

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Fig: An Abstract view of Computer system/components

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User and System View

User perspective : ease of usage is the main

consideration.

System perspective : efficiency in usage ofresources is the main consideration.

As a provider of resources - OS must have a

policy and a control program to regulate theallocation of resources.

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Task/Work/Functions of OS

Interface

Storage Management

Schedules the resources

Device Management

Facilitating Networking

Security to user

Control & allocate memory Decides priority of application programs

Interrupts etc.

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Batch OS

Process for job took a lot of time & no user

interaction.

Jobs with similar needs where batched together &run through the computer.

User are not required to wait while the jobs was

processed. They can submit their programs &return later to collect the output.

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Features of Batch O.S

1. Process Scheduling

Allocation process for job to a processor is called

as process scheduling.

System uses FCFS criteria.

Another criteria Shortest Job next.

2. Memory Management

Memory divided into two parts:a) O.S

b) User program Area

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Fig: Memory layout for a simple Batch O.S

Operating

System

User Program

Area

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3. File Management

Batch O.S provides the serial file management

for accessing so that no need of concurrency

control is required.

4. I/P & O/P Management

Since only one program or batch used to beunder execution at a time, so there is no

contention for allocation of I/O devices.

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Disadvantages of Batch O.S

1. Non- interactive

2. Off line debugging

3. More waiting time

4. More time requirement for creation of

batches.

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Multiprogramming OS

Late 60s and early 70s Storing multiple executables (at the same time) in the main

memory is called multiprogramming.

With multiple executables residing in the main memory, theimmediate consideration is: we now need a policy to

allocate memory and processor time to the resident

programs.

By utilizing the processor for another process when a

process is engaged in input or output the processorutilization and, therefore, its output are higher.

Multiprogramming leads to higher throughput.

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Time Sharing OS

Multiple users access the system.

Each one gets a time-slice for his job.

Users get an illusion as if he has the whole

system for himself.

Time shared systems must inherently support

multiprogramming.

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Real Time O.S

RTOS have fixed time constraints.

Primary objective is to provide quick event

response time & meet the scheduling deadline.

User convenience & resource utilization aresecondary concerned.

Divided into two parts:

1. Soft Real Time System

2. Hard Real Time System

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Features of RTOS

1. Memory Management

It is less demanding than other type of systems.

Reason: many process permanently reside in

memory in order to provide quick response.

2. Input-Output Management

RTOS provides system calls to execute the

process & gives the resultant output.

3. File Management

Satisfies the requirement of protection & access

control.

Objective to speed up the access.

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Multiprocessor System

Also called as Parallel System.

Has two or more processor in close

communication & sharing the computer bus &memory & other peripherals.

Are of two types:

1. Asymmetric multi processor

2. Symmetric multi processor

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1. Asymmetric multiprocessor

Every processor is assigned a specific

task.

A Master processor controls the system.

Other processes either look to master for

instruction or as predefined task.

Scheme defines master-slave relation.

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2. Symmetric Multiprocessor

Every processor performs all tasks within one as

& communicate within one another as needed.

Simple means that all processors are separate &

no master slave relationship exists b/w the

processors.

CPU CPU CPU

Memory

Fig: Symmetric multiprogramming

Architecture

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Advantages of Multiprocessor

1. Increased Throughput

Increasing no. of processors get more work done

in less time.

Speed of ratio with N processor is not N it is

less than N. Due to overheads and contention.

2. Cost Effective

Saves more money than multiple singleprocessor because they can share various

peripherals, storage systems & power supply.

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Advantages of Multiprocessor

3. Increased Reliability

Failure of one processor will not stop the system.

If one processor fails the other will take over &

share the work of failed processor.

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Distributed OS

Distributed Means Data is Stored and Processed

on Multiple Locations.

When a Data is stored on to the Multiple

Computers, those are placed in DifferentLocations.

Distributed means In the Network, Network

Collections of Computers are connected with

Each other. In this Data is shared between many users. And

we can also Access all the Input and Output

Devices are also accessed by Multiple Users.

Documents

OS_LECT1&2