Salient Features of Unix Commands in unix and unix components

 

 Salient Features of Unix:

 

In unix there are mainly four features that 

are,

1.Multitasking

2.Multiuser

3.portable

4.Device independent 

 
1.Multitasking: Unix has ability to support concurrent execution of two or more active process.

2.Multiuser: Unix has ability to support more than one user to login into the system simultaneously and execute program, multiple  users can access the system by connecting to points  known as terminals.

3.Portable: Unix operating system is highly portable compared to other operating systems, it is very easy to port Unix on to different hardware platform with minimal or no modeification at all.

4.Device independent: Unix has a very well organized file or directory system that allows users to organize and maintain these files or directories easily or efficiently.

    Commands in unix:

In unix there are two types of commands, 

  1)External command and

  2)Internal  command.

 1)External command:-

A command with an independent existence in the form of separate file is called External command.

Example:ls command is stored in file /bin/ls.Most of Unix commands are external in nature's. -programs for the command such as cat and ls, exist independently in a directory called /bin directory.

2)Internal  command:-

A command that does not have an independent existence is called Internal command.

Example:echo commandos is an internal command as it's routine will be part of the shells routine ,sh.

 
 components in unix:


 In unix it consist three major components
that are 

1.The kernel

2.The shell

3.The file system


1.The kernel: The kernel is heart of any operating system. it is collection of program
that are mostly written in c and it get automatically loaded on the memory as soon as the system is booted. It manages the entire resources of the system.


Functions performed by the kernel are: 

•Managing the machine memory and allocating it to each process.

•Scheduling the work done by the cpu so that the work of each users is carried out.

•Organizing the transfer of data from one part of machine to another.

•Enforcing the access permission that are in force on the file system.


2.The shell:A shell is a program that sits on kernel acts as interface between the users and  kernel hence hardware. A shell is command interpreteror a process it presents a command line prompt [usually a $  or a % symbol] at which the user can type in any Unix command.

it takes each command and passess it to the operating system kernel which works on it. It then displays the results of this operating on the screen.


Types of shell:There are different types of shells are available some are

The Bourne shell  (sh): This is original Unix shell written by Steve Bourne at AT &Bell labs.this shell does not have interactive facilities.

The C Shell (csh): bill joy developed this shell at university of California Berkely (UCB) as a part of the BSD release. It is called the c-shell because its  syntax and usage similar to come programming language.

The korn shell (ksh): This shell was developed by David korn at AT & T Bell labs. Basically it is built on bourne shell. It also provides intreactive of the C Shell korn shell. It's programming language is compatible with Bourne shell.


The file system: Unix treats everything including hardware device as a file. All the files know Unix system are organized in inverted tree-like hierarchical structure. This structure arrangement in which files are stored referred as file system.