Lecture By :

Rupinder Kaur

Lect. IT

SRS Govt. Polytechnic college Ludhiana

Topic : Overview of Operating System

Software

Software :

- Software is a set of various programs which are used to operate computers and related devices.

- Softwares are designed to achieve a specific goal.

Types :

- System Software

- Application Software

Types of Software

System Software : -Performs essential operation tasks–Operating system –Utility programs

Application Software : -Performs specific tasks for users–Business application–Communication application–Multimedia application–Entertainment and educational software

Computer System Components

Hardware – provides basic computing resources (CPU,memory, I/O devices).

Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.

Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (database systems, video games, business programs).

Users (people, machines, other computers)

Definition of OS

An operating system (OS) is software, consisting of programs and data, that runs on computers, manages computer hardware resources, and provides common services for execution of various application software.

A program that acts as an intermediary between a user of a computer and the computer hardware.

Example of OS

• Network Operating System

– UNIX / Linux / MS Windows2000 Server• Desktop Operating System

–MS Windows 9X/Me / Mac OS / DOS• Mobile Operating System

–Palm OS and Pocket PC

Operating system goals

Convenience– Makes the computer more convenient to use

Efficiency– Allows computer system resources and other

hardware to be used in an efficient manner Ability to evolve

– Permit effective development, testing, and introduction of new system functions without interfering with service

Operating System Services

Program development Program execution Access to I/O devices Controlled access to files System access Communication

Error detection – Hardware errors– Memory errors– I/O device errors– User program errors– Power Failure

Resource Allocation Accounting Protection

Operating System Services (cont..)

Operating system Functions

Process Management Main Memory Management File Management I/O System Management

Operating system Functions (cont..)

Secondary Memory Management Networking Protection System

Process Management

A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task.

Process Management (cont..)

The operating system is responsible for the following activities in connection with process management.- Process creation and deletion.- Process suspension and resumption- Provision of mechanisms for:

✔ process synchronization ✔ process communication

Main Memory Management

Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices.

Main memory is a volatile storage device. It loses its contents in the case of system failure.

Main Memory Management (cont..)

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

File Management

A file is a collection of related information defined by its creator. Files represent programs (both source and object forms) and data.

File Management (cont..)

The operating system is responsible for the following activities in connections with file management:‾ File creation and deletion.‾ Directory creation and deletion.‾ Support for manipulating files and directories.‾ Mapping files onto secondary storage.‾ File backup on stable (nonvolatile) storage

media.

I/O System Management

The I/O system consists of:‾ A buffer-caching system‾ A general device-driver interface‾ Drivers for specific hardware devices

Secondary Memory Management

Main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.

Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.

Secondary Memory Management (cont..)

The operating system is responsible for the following activities in connection with disk management:‾ Free space management‾ Storage allocation‾ Disk scheduling

Networking

Network (also called distributed system) means interconnection of two or more than two autonomous computers.

A distributed system is a collection processors that 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.

Networking (cont..)

A distributed system provides user access to various system resources.

Access to a shared resource allows:‾ Computation speed-up‾ Increased data availability‾ Enhanced reliability

Protection System

Protection is a mechanism for controlling access by programs, processes, or users to both system and user resources.

The protection mechanism must distinguish between authorized and unauthorized usage.

Types of OS

Batch processing or Mainframe Systems

Desktop SystemsTime-Sharing SystemsMultitasking OSMultiprogramming

Types of OS (cont..)

Multiprocessor or Parallel SystemsDistributed SystemsClustering SystemReal-Time SystemsHandheld Systems

Batch Processing Systems

Jobs, together with input data, are fed into the system in a batch.

Reduce setup time by batching similar jobs

The jobs are then run one after another.

Batch Processing System (cont..)

No job can be started until previous job is completed.

Automatic job sequencing – automatically transfers control from one job to another

Desktop Systems

Personal computers – computer system dedicated to a single user.

I/O devices – keyboards, mouse, display screens, small printers.

User convenience May run several different types of

operating systems Examples : Windows, Mac OS, UNIX,

Linux

Time-Sharing Systems

Each user is given a time slice to interact with the CPU.

The size of the time slice will depend on the system.

Each user is served in sequence.

Multiprogramming

In multiprogramming OS processes more than one applications at one time.

Two or more programs store in the main memory at the same time

Multitasking OS

It is the extension of multiprogramming.The concept of multitasking is quite

similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running.

Multiprocessor or Parallel Systems

Multiprocessor systems with more than on CPU in close communication.

Types of multiprocessor systems :

1) Tightly coupled processors

2) Loosely coupled processors

Multiprocessor or Parallel Systems (cont..)

1 )Tightly coupled system or Symmetric multiprocessing (SMP) :

– processors share memory and a clock; communication usually takes place through the shared memory.

- Each processor runs and identical copy of the operating system.

- Most modern operating systems support SMP

Multiprocessor or Parallel Systems (cont..)

Multiprocessor or Parallel Systems (cont..)

2) Loosely coupled system or Asymmetric multiprocessing (ASMP) :

– each processor has its own local memory; processors communicate with one another through various communications lines, such as high speed buses or telephone lines.

- Each processor is assigned a specific task; master processor schedules and allocated work to slave processors.

Multiprocessor or Parallel Systems (cont..)

Advantages of parallel system: Increased throughput Economical Increased reliability

Distributed Systems

Distribute the computation among several physical processors.

Requires networking infrastructure.Local area networks (LAN) or Wide

area networks (WAN)May be either client-server or peer-to-

peer systems

Distributed Systems (cont..)

Advantages of distributed systems.

- Resources Sharing

- Computation speed up

- Reliability

- Communications

Client Server

- Client-server architecture can be considered as a network environment that exchanges information between a server machine  and a client machine where server has some resources that can be shared by different clients.

- In a Client/server architecture individual computers (known as clients) are connected to a central computer which is known as server.

Client Server (cont..)

Peer to Peer (P2P)

In P2P networking each workstation has equivalent capabilities and responsibilities.

Clustering System

Clustering allows two or more systems to share storage.

Provides high reliability. Asymmetric clustering: one server runs

the application while other servers standby. Symmetric clustering: all N hosts are

running the application

Real-Time Systems

Real time OS are used under strict timeline or deadline boundaries.

Often used as a control device in a dedicated application such as controlling scientific experiments, medical

Well-defined fixed-time constraints.

Real-Time Systems (Cont..)

Hard real-time:- A hard real time system is the system that

guarantees the completion of a particular job within certain time limit.

Examples : controlling scientific experiments, medical imaging systems, industrial control systems

Real-Time Systems (Cont..)

Soft real-time- A soft real time system is the system that can

not fully guarantees the completion of a particular job within the certain time limit.

- These system are based on priorities.- Examples : Mobile phone, digital cameras

Handheld Systems

Personal Digital Assistants (PDAs) Cellular telephones Issues:

- Limited memory

- Slow processors

- Small display screen

Buffering

A temporary storage area (buffers) to read data from input device or send data to the output device

keep CPU busy–because I/O operation is slow Reading and writing data from hard disk takes long

time. so to improve the speed for data processing the data next required by processor is stored is cache memory or CPU register. for e.g. to cut certain line from text file to copy into another file. cut data get stored in to buffer (CPU register) to get back stored into another file.

Spooling

Spooling is the process of a sending data to a spool, or temporary storage area in the computer's memory. This data may contain files or processes.

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