Operating System

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Operating system :

· An Operating system is a system software acts as a communication bridge/interface between the user and computer hardware.

· The purpose of an operating system is to provide a platform on which user can execute in a convenient and efficient manner.

· An operating system a piece of software that manage the allocation of computer hardware. The coordination of the hardware must be appropriate to ensure the correct working of the computer system and to prevent user programs from interfering with the proper working of the system.

· The main task of an operating system is to carried out is the allocation of resources and services, such as allocation of memory, devices, proceses and information.

· The operating system also includes program to manage these resources, such as a traffic controller, a scheduler, memory management module, I/O programs and a file system.

· Operating system is an integrated set of specialized programs used to manage overall resources and operations of the computer.

· Operating system is a specialized software that controls and monitors the execution of all other programs that reside in the computer.

Objectives of operating system :
·       An operating system makes a computer more convenient to use.
·       Operating system allows the computer system resources to be used in an efficient manner.
·        Operating system should be constructed in such a way as to permit the effective development, testing and introduction of new system functions without interfering with service.
·        Operating system acts as an intermediary between the hardware and its users, making its easier for the user to access and use other resources.
·        Keep track of who is using which resource, granting resource request from different programs and users.

·        Operating system provide efficient and fair sharing of resources among user and programs.

Functions of operating system :
1.   Security :- Operating system uses password protection to protect user data and similar other techniques. Is also prevents unauthorized access to programs and user data.
2.   Job Accounting :- Operating system keeps track of time and resources used by various tasks and users, this information can be used to track source usage for a particular user or group of user.
3.   Error detecting aids :- Operating system constantly monitors the system to detect errors and avoid the manufacturing of computer system.
4.   Coordination between other software and users :- Operating systems also coordinate and assign interpreters, compilers, assemblers and other software to the various of the computer systems.
5.   Memory management :- The operating system manages the primary memory/Main memory.
§ Main memory is made up of large array of bytes.
§ Main memory is a fast storage and it can be accessed directly by CPU.
§ For a program to be executed, it should be first loaded in the main memory.
6.   Processor Management :- In multi-programming environment, the operating system decides the order in which processes have access to the processor, and how much processing time each process has.
7.   Device Management :- An Operating System manages device communication via their respective drives.

8.   File management :- A file system is organized into two directories for efficient or easy navigation and usage. These directories may contain other directories and other files.

Need of Operating System :

· Operating system is a software which manages and control the entire set of resources and effectively utilize every part of a computer.

· The fundamental goal of operating system is to execute user programs and to make tasks easier.

· Operating system provides a platform on which application programs can run. These application programs help the users to perform specific task easily.

· Operating system is designed in such a manner that it operates, controls, and executes various applications on the computer.

· Operating system also allows the computer to manage its own resources, such as memory, keyboard. printers etc. Management of these resources is required for an effective utilization.

Memory :

· Memory is internal storage area in the computer system.

· Memory is the most essential element of a computing system because without it, computer can’t perform even simple tasks.

Types of memory :

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1. Primary memory/Volatile memory :

RAM (Random Access Memory) :

· RAM is also called read write memory or primary memory or main memory.

· The programs and data that the CPU requires during execution of a programs are stored in this memory.

· It is volatile memory as the data loses when the power is turned off.

Types of RAM :

DRAM	SRAM
Constructed of tiny capacitors that leak electricity.	Constructed of circuits similar to D flip-flop
Requires recharge every few miliseconds to maintain data.	Hold contents as long as power is available.
Slower than SRAM.	Faster than DRAM.
Uses less power.	Uses more power.
Generates less heat.	Generates more heat.
Used for main memory	Used for cache.

2. Secondary memory/Non-volatile memory :

ROM (Read Only Memory) :

· ROM stores crucial information essential to operate the system, like the program essential to boot the computer.

· ROM is used in embedded systems or where the programing needs no change.

· ROM is non-volatile, always retains its data.

· It is also used in calculators.

Types of ROM :

PROM	EPROM	EEPROM
It can be programed by user.	It can be re-programmed by user.	The data can be erased by applying electric field.
Once programmed, the data and instruction in it can’t be changed.	To erase data from it, expose it to U.V light. To re-programed it, erase all previous data.	We can erase only portions of the chip.

Diference between RAM and ROM :

RAM

ROM

Temporary storage

Permanent storage

Store data in M.Bs

Store data in G.Bs

Used in normal operations

Used for startup process of computer.

It is volatile

It is non-volatile

Client :

A client is the receiving end of a service, which can be accessed via a network.
A client is a simple application or whole system that accesses service being provided by a server.
A client is connected to a server through sockets, shared memory or Internet protocols etc.

Server :

A server is a computer, a device or a program that is dedicated to managing network resources.
Server computers often have special operating systems not usually found on personal computers(PCs).
Dedicated servers may have high-performance RAM, faster processor and high-capacity hard drives.

Client-Server Architecture :

Client-Server Architecture is a computing model in which the server hosts, delivers and manages most of the resources and services to be consumed by client.
This type of architecture has one or more computers connected to a central server over a network or Internet connection.
Client server architecture works when the client computer sends a resource or process request to the server over the network connection, which is then process and delivered to the client.
A server computer can manage several clients simultaneously. It is also known as Networking computing model or Client-Server Network. Because all the requests and services are delivered over a network.

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Server acts as a ‘Producer’ and Client acts as a ‘Consumer’.
The Internet is also based on Client-Server Architecture where Web-Servers serve many simultaneous users with website data.

Time sharing system :

Time sharing is the distribution of a computing resource to many users via multi-programming or multi-tasking.
Users are able to access the same computer through different terminals and were promoted when it was their turn.
In sharing systems, all the tasks are given specific time and task switching time is very less.

Example of sharing operating system are -

1. Multics

2. Unix

Purpose of Time-sharing system :

The first Time-sharing project was implemented by John McCarthy in 1957 using a modified IBM 704.
Time-sharing system was introduced in 1960s, when computers were still too expensive.
The solution was to allow many users to make use of one computer by a specific duration of time that a user could access the computer.
Extended form of Time-sharing is Multi-tasking which is logical extension of multi-programming.

Advantages of Time-sharing system :

Specific duration of time provided, that a user could access the computer, which most people could not afford.
Many applications can run at the same time and also use Time-sharing in batch systems, which increase performance.
Time-sharing system is better way to run a busines, having a lot of tasks to be done. Each task and each user get its time.

Multi-programming system :

In multi-programming system, there are one or more programs loaded in main memory, which are ready to execute.
Multi-programming s system, when one program is waiting for I/O, there is another program ready to utilize the CPU.
It does not execute many jobs at the same instant of time. There are number of Jobs available in CPU (Main Memory) and a portion of one is execute, then a segment of another and so on.
Multi-programming in which several programs are run at the same time on Uniprocessor.

Purpose of Multi-programming system :

To overcome the problem of utilization of CPU (Main Memory) the multi-programming was introduced.
Multi-programming is interleaved execution of multiple jobs by the same computer.
Multi-programming is a common approach to resource management.

Difference between Time-sharing and Multi-programming system :

Time-sharing	Multi-programming
All the tasks are giving specific time and task switching time is very less.	Several programs are run at the same time on uniprocessor.
Users are able to access the same computer through different terminals.	Execution of multiple jobs by the same computer.
It is better way to run a business, having lot of tasks to be done.	When one program is waiting for I/O, another program is ready to utilizes the CPU.
Multiple processes are managed simultaneously which requires an adequate management of main memory.	User gives instruction to the program directly and receives and immediate response.
It provides direct access to a large number of users where CPU time is divided among all the users on scheduled basis.	Multiple jobs are executed by CPU simultaneously
Allows multiple users to use a computer system at a time.	Allows multiple tasks or processes to use a computer at a time.
CPU time is shared by different processes.	One job selected and run via job scheduling.
CPU is taken away from a running process, when the allotted time slice expired.	The first job finished waiting and gets the CPU back.

Subjects

Operating System | Book | Notes | Practicals download pdf | B.Sc-[IT]