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UNIX Operating System

Article No: 1
WHAT THE UNIX SYSTEM IS?
To understand how the UNIX System works, you need to understand its structure. The UNIX operating system is made up of several major components. The components include the kernel, the shell, the file system, and the commands (or user programs).
Tools and Applications
The UNIX system contains several hundred utilities or user programs. Commands are also known as tools, because they can be used separately or put together in various ways to carry out useful tasks. You execute these utilities by invoking them by name through the shell; this is why they are called commands.
You can use applications built using UNIX commands, tools, and programs. Application programs carry out many different types of tasks. Some perform general functions that can be used by a variety of users in government, industry, and education. These are known as horizontal applications and include such programs as word processors, compilers, database management systems, spreadsheets, statistical analysis programs, and communication programs. Others are industry-specific and are known as vertical applications. Examples include software packages used for managing a hotel, running a bank, and operating point-of-scale terminals.
The File System
The basic unit used to organize information in the UNIX system is called a file. The UNIX file system provides a logical method for organizing, storing, retrieving, manipulating, and managing information. Files are organized into a hierarchical file system, which files grouped together into directories. An important simplifying feature of the UNIX system is the general way it treats files. For example, physical devices are treated as files; this permits the same commands to work for ordinary files and for physical devices; that is printing a file (on a printer) is treated similarly to displaying it on the terminal screen.
The Shell
The shell reads your commands and interprets them as requests to execute a program or programs, which it then arranges to have carried out. Because the shell plays this role, it is called a command interpreter. Besides being a command interpreter, the shell is also a programming language. As a programming language, it permits you to control how and when commands are carried out.
The Kernel
The kernel is the part of the operating system that interacts directly with the hardware of a computer, through device drivers that are built into the kernel. It provides sets of services that can be used by programs, insulating these programs from the underlying hardware. The major functions of the kernel are to manage computer memory, to control access to the computer, to maintain the file system, to handle interrupts (signals to terminate execution), to handle errors, to perform input and output services (which allow computers to interact with terminals, storage devices, and printers), and to allocate the resources of the computer (such as CPU or input/output devices) among users.
Programs interact with the kernel through approximately 100 system calls. System calls tell the kernel to carry out various tasks for the program, such as opening a file, writing to a file, obtaining information about a file, executing a program, terminating a process, changing the priority of a process, and getting the time of day.

Made By: Chaudhary Amit V.
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