UNIX COMMANDS EX No 1 STUDY OF UNIX OPERATING SYSTEM - Computer Programming

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Wednesday, October 27, 2010

UNIX COMMANDS EX No 1 STUDY OF UNIX OPERATING SYSTEM


UNIX COMMANDS

EX No 1                        STUDY OF UNIX OPERATING SYSTEM

An operating system (commonly abbreviated OS and 0/5) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the limited resources of the computer. The operating system acts as a host for applications that are am on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware..
                       Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation.
                                                 Under Unix, the “operating system” consists of many of these utilities along with the master control program, the kernel. The kernel provides services to start and stop programs, handle the file system and other common “low level” tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between user-space and kernel-space.
 I.Kernel
2.Shell
3. User’s shell programs.
                 It is the main part of the operating system. It controls all the resources, users, hardware and tasks that are present in the system. So we can define kernel as the Master program which act as the heart of the operating system.

Shell

1. Receives user command from the shell
2. Communicates with the hardware.
3. Control all the computer resources
4. Runs scheduler.
5. Run all the programs.


            The user cannot directly interact with the kernel. During the login of the user the kernel starts an interactive program for each user. This program is known as shell. The shell acts as an interface between the user and kernel. The shell will act as an interpreter. When user gives some command the shell anaiyses those commands and passes them to the kernel. The kernel then submits these commands to hardware and the required actions are carried out. This process is shown below:




PARTS OF UNIX OPERATING SYSTEM

The UNIX operating system have three parts. They are
Kernel



 FILES AND DIRECTORIES

A file is a collection of information that is assigned a name that is used to identify that file. The file is always stored in secondary storage medium. A directory is a special type file that contains a list of file names. All files are grouped together into directory for easier access. A directory can have one or more directories rn it called sub-directories.
In LINUX files and directories are arranged in a hierarchical manner.

 DIRECTORY HIERARCHY OF UNIX
In UNIX every file is assigned to some directory. The root directory is the main directory and named as ‘I’. All the other files and directories are its subdirectories.


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