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
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