What is an Operating System (OS).| Types of Operating system.?

An Operating System (OS) is a software that acts as an interface between computer hardware components and the user. Every computer system must have at least one operating system to run other programs. Applications like Browsers, MS Office, Notepad Games, etc., need some environment to run and perform its tasks. 

Operating System is a system software . There are a number of  Operating system . Single , Multi-   Programming , Multi-tasking are few terms very much familiar with the operating system and how   to  work on same prominent operating system.

Operating system is the first Software that loads after the computer starts . it means it is a mandatory   software for booting your computer system . it is not only mandatory for booting computer system   but is also essential for running other application software & utility software .

Operating system plays an important role in computer. As one know computer is an electronic device . it can perform the task according to computer given instruction . computer system can be divide in      to four components 

1. Hardware

2. Operating System

3. Application program

4. User's

 In this 4 components OS is a software program. 

  Operating system is Mysterious Power which control all hardware and software on computer . It work as a mediator between hardware and software . just because of the OS. The programmer don't need to know the complexity of hardware program communicate with hardware through OS.

 Your computer has mainly resource such as memory , Hard disk , CPU , keyboard , Network ,co-ordination etc. The most important objectives of Operating system is to organism them resource . An OS ensure that all the application get proper hardware resources as required and the application get enough CPU times to get their commands processed and they enough memory to store data.

 An OS is provide user interface which helps the user to give commands to the OS to run the application of their choice . Today OS provide us graphical interface ,where , instead of typing the commands they are clicked and double click to get them implemented. 

                  Today are many operating system in market but all have same fundamentals but their functional method are different.they functional method are depends upon how they are designed.

Every program running on a computer , be it background services or application , is a process as long as the von Neumann architecture used build computer. only one process per CPU could be run at a time . Older microcomputer OS such as MS_DOS , did not attempt to bypass this limit , with the exception of interrupt processing , only one process could be run under them.

    .Process management is an operating system's way of dealing with running multiple processes.since most computer contain one processor with one (or more) core.multitasking is done by simply switching process quickly, depending on  operating system. In many system there is a background process , such as the system idle process in window, which will run when no other process is waiting for the CPU.

Current computer architecture arrange the computer's memory in a hierarchical manner.starting from fastest register , CPU cache, ran and disk storage memory management is the act of managing computer memory. The management of main memory is critical to the computer system.

   The basic objective of memory management system it is provide fast-uninterrupted access by the processor to the memory such that the processor can operate at the speed it is expected to work.

An Operating system  memory manager coordinate the use of these various types of memory by tracking which one is available , which is to be allocate or deallocate and how to move data between and how to move data between them . this activity , usually referred to as virtual memory  management.increasing the amount of memory available for each process by making the disk storage seem like main memory.There is a speed penalty associate with using disks or other slower storage as memory, if running process required significantly more RAM than is available , the system may start trashing . This can happen either because one process requires a large amount of a memory than is available/ This leads transfer of each process of data to slower storage.

Another important part of memory management is managing virtual address.

Main memory is divide into two parts:-

The area of main memory which can be accessed by user process and in this only operating system resides.

This is the part of main memory where space for the user process allocate.

 All operating system include support for a variety of file systems .Modern file system comprise of a hierarchy of dir . While the ideas is conceptually similar across all general purpose file system, some different in implementation exists . Two noticeable example of this are the same char used to seprate dir , & case sensitivity.

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A distributed system is a group of processors which do not share memory, hardware devices, or a clock. The processors communicate with one another through the network. .

Typically an OS offers various services to other network computer and users These services are usually provides through ports or numbered access points beyond the OS network add. Typically services include offering such as file sharing , print service,email,web site, FTP.

               At the front line of security are hardware device know as firewalls . at the OS level , there are a number of software firewalls available.

Device Driver:-

A Device Driver is specific type of computer software developed allow interaction with hardware. device Typically this consists an interface for communicating with device , through specific computer bus or communications subsystem that the hardware is connected to, providing commands to and receiving data 

from the device.

Batch operating system

The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches.

The problems with Batch Systems are as follows −

• Lack of interaction between the user and the job.
• CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
• Difficult to provide the desired priority.

Real Time operating System

A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing.

Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.

There are two types of real-time operating systems.

Hard real-time systems

Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.

Soft real-time systems

Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.

Multi-Tasking/Time-sharing Operating systems

Time-sharing operating system enables people located at a different terminal(shell) to use a single computer system at the same time. The processor time (CPU) which is shared among multiple users is termed as time sharing. 

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