UNIT: 6. UNIX Case Study

Introduction of UNIX:

UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops. UNIX is used to complete some critical operation related with hardware & software.

UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren’t covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session. There are many different versions of UNIX, although they share common similarities. The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.

  1. Draw & explain UNIX OS Structure.

Ans: The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs

and handles the file store and communications in response to system calls. As an illustration of the way that the shell and the kernel work together, suppose a user type’s rm my file (which has the effect of removing the file my file). The shell searches the file store for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on my file. When the process rm my file has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.


Amongst the functions performed by the kernel are:

  • Managing the machine’s memory and allocating it to each process.
  • Scheduling the work done by the CPU so that the work of each user is carried out as Efficiently as is possible.
  • Organizing the transfer of data from one part of the machine to another.
  • Accepting instructions from the shell and carrying them out.
  • Enforcing the access permissions that are in force on the file system.

The shell:

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems). The user can customize his/her own shell, and users can use different shells on the same machine. The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands. You can use any one of these shells if they are available on your system. And you can switch between the different shells once you have found out if they are available.

Bourne shell (sh), C shell (csh), TC shell (tcsh), Korn shell (ksh).

  1. Describe stepwise booting process of UNIX along with diagram.

Ans: The loading of the operating system is achieved by a special program called BOOT. Generally this program is stored in one (or two) sectors on the disk with a pre-determined address. This portion is normally called „BOOT Block‟ as shown in fig. The ROM normally contains a minimum program. When one turns the computer „ON‟, the control is transferred to this program automatically by the hardware itself. This program in ROM loads the BOOT program in pre-determined memory locations. The beauty is to keep BOOT program as small as possible, so that the hardware can manage to load it easily and in a very few instructions. This BOOT program in turn contains to read the rest of the Operating System into the memory. This is depicted in figures. The mechanism gives an impression of pulling oneself up. Therefore, the nomenclature bootstrapping or its short form booting.

  1. Compare UNIX & LINUX.





Second Sessional Question Bank:

  1. Draw & explain I/O burst & CPU burst in short.
  2. Compare Preemptive & Non preemptive scheduling.
  3. Explain different process scheduling criteria.
  4. Explain FCFS scheduling algorithm & calculate AWT of the following:
Process Burst Time
P1 24
P2 3
P3 5
  1. Solve following by Preemptive SJF & RR Scheduling Algorithm: (Time Slice=4)
Process Arrival Burst Time
P1 0 8
P2 1 4
P3 2 9
P4 3 5
  1. Explain Attributes of File (Any 8).
  2. Explain the concept of Swapping. 8. Draw & explain Index File Allocation Method. 9. Draw & explain Index Memory Allocation.  10. Explain page replacement FIFO & solve (4 5 6 7 4 5 8 4 5 6 7 8). 11. Compare UNIX & LINUX (any 6 Points). 12. Explain Necessary condition for Deadlocks. 13. Explain Bankers Algorithm. 14. Explain SRTN algorithm with example. 15. Explain Round Robin algorithm & calculate ATT & AWT: (TS=5)
Process Burst Time
P1 24
P2 3
P3 5
  1. Explain in detail operation perform on the Files. 17. Draw & explain Continuous Memory allocation strategies. 18. Explain concept of Virtual Memory. 19. Differentiate between Paging & Segmentation. 20. Explain Page Replacement LRU & solve following: (Frames= 3) (4 5 6 7 4 5 8 4 5 6 7 8).  21. Draw & explain structure of UNIX. 22. Explain File accessing Method in detail. 23. Explain Demand paging in detail. 24. Explain Multilevel Feedback Queue Scheduling. 25. Explain Multiprocessor Scheduling Algorithm in detail.

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