STRUCTUER OF UNIX

1.   KERNAL:- The kernel of the UNIX is first layer which runs on actual machine hardware and interact with hardware effectively. Kernel is so called because it is the heart of UNIX. It is the master program which controls the computer’s resources. It allocates resources such as memory, disk etc to perform various tasks.

          At a particular moment there may be several SHELLS running in memory but only one KERNAL controls, process the field system operations and other function required by operating system. The kernel also manages the memory that is key element of system.

“KERNAL is the layer of UNIX that provides the core capabilities of system and allows process to access hardware in an orderly manner”.

     FUNCTIONS OR FEATURES OF KERNAL

·        It keeps the track of various program being executed allocating time slice to each of them.

·        It assigns storage for every file and handles the transfer information between computer and terminals.

·        Execution of commands is search out immegately because KERNAL is always resident in main memory.

·        Controls hardware resources such as printer, tape drives and other peripheral if any.

·        Managing file creation, storage and access.

·        Setting priority, controlling and executing various jobs.

·        Checking and controlling the access to the computer for the users.

·        Works as device manager and perform the useful functions for processes which need an access to peripheral devices connected to the computer.

·        Manage the processes that need to communicate with one another, sending and receiving information that allows other actions to be perform.

SHELL:- The SHELL envelop the KERNAL. In other words “SHELL act as an interface between user and KERNAL”.

The UNIX operating system is made up of two parts:-

First is the layer of system program and second part is SHELL which interprets and manages the execution of these program.

“The shell is command line interpreter that interprets the commands entered by users”.

  

The SHELL keeps the list of commands, you have type in. The SHELL is command line interpreter that enables the users to interact with operating system. Every user once accepted by the KERNAL is issued a SHELL prompt. Each user has his own SHELL and command issued by him are founded serially. The SHELL waits for input from the user and submitted to the KERNAL to execute the program.

                 FUNCTIONS OF SHELL

·        Execution of command for piping and filtering actions.

·        Tools for carrying out foreground and background process.

·        Utilities for configuring the hardware.

·        Input-output redirection and command execution utilities.

·        File name substitution.

·        Reads user input from the command line and executes actions based upon that input.

               TYPES OF SHELL

There are three types of shell in UNIX. That are:-

·        BOURNE SHELL

·        C SHELL 

KORN SHELL