Introduction to UNIX Operating System

 Why UNIX? What is UNIX? Why Unix so Popular as a server?

    

     What is an operating system?

               A simple answer is Operating system is nothing but a set of programs that acts as an interface between user and computer(Hardware).

   How operating system can be classified?

             An operating system can be categorized based on user and task managing capabilities.

    1. Singe task single user operating system.(ex. MS DOS)

    2.  Multi task single user operating system.(ex Windows)

    3. Multi task multi user operating system.(ex. UNIX operating system)

   

    I think you all are well familiar with MS DOD and Windows. In MS DOS we can execute only one task at a time. 

  for example 

  

         c:\>copy con raj

        hi raj this is raj 

       Am doing my M.Tech   (after typing u type ctrl+z to save your program)

   for example imagine that while your are typing data into a file you wanna see list of files in your directory(dir command is used to list the files in your directory). Will it works? definitely no! Because in a single tasking operating system at a time only one task will be executed.

   Now coming to multitasking operating system (for example consider Windows) we can execute  multiple tasks at the same time. For instance you can open a file for writing purpose mean while you can listen songs and send copy data from your system to a pen drive. 

  Now one more question is how many persons can use the MS DOS and Windows system(resources) at the same time. Definitely your answer is one! 

Now coming to UNIX Operating system a single system can be used by multiple users at the same time and can be done several tasks the same time. You just need DUMB terminals to connect to UNIX operating system. Where as  in windows you need to have separate operating system for each user to connect to windows server.

   Confused????

       let me clarify your confusion. In windows also we can share resources using windows server. But the problem in windows is we need to have separate operating system for each user to connect to server. Where as to connect to UNIX server we need a minimum configuration in each individual system. What ever programs you do they will be saved in UNIX server only. i.e., for each user, some space will be allocated in UNIX operating system and the user need only user name and password to connect to server. After a user connected to the server all the files that user reading writing will be saved in UNIX server only.

      

      The heart of UNIX Operating system is kernel. Kernel acts as interface between user and hardware. 

What is kernel?

      Kernel(contains init() program)  is nothing but a basic program(just like bootstrap loader program in windows) which will load UNIX environment in to our system. It is the parent(base) process of all other sub(child process). Simply to tell init() program will start first in UNIX then child process (for example terminal window) creates. Kernel acts as an interface between programs and hardware. 

Shell acts as an interface between application programs Kernel. we have different types of shells in UNIX. 

1.Bourne shell

2. C shell

3. korn shell etc.

Note We are going to do shell programs in next chapters. So now am skipping topic about shell. 

just remember shell programs are used to combine and execute different commands at the same time.

Above shell they are user programs like java programs,c programs, text editor etc. What ever program you type or execute first it must go through shell then to kernel. So it is important to learn shell basics to get good grip on UNIX operating system.

   

                (to be continued) 

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