OS-B.C.A-Sem3-September-2019

Name   …………………………… Roll No ……………………….

SAINTGITS COLLEGE OF APPLIED SCIENCES

SECOND INTERNAL ASSESSMENT EXAMINATION, MARCH 2019

Department of   B.C.A  , Semester III

OPERATING SYSTEMS ANSWER KEY

Total    : 80 marks                                                                                          Time:3Hours

Section A

Answer any 10 questions. Each question carries 2 marks.

1.      What do you mean by multi-programming?

Multiprogramming is a rudimentary form of parallel processing in which several programs are run at the same time on a uniprocessor. Since there is only one processor, there can be no true simultaneous execution of different programs

2.Explain OS structure?

An operating system is a construct that allows the user application programs to interact with the system hardware. Since the operating system is such a complex structure, it should be created with utmost care so it can be used and modified easily

3.Explain the term process?

A process is an instance of a program running in a computer.

4.Explain long term and short term Schedulers?

The short-term scheduler (also known as the CPU scheduler) decides which of the ready, in-memory processes is to be executed (allocated a CPU) after a clock interrupt, an I/O interrupt, an operating system call or another form of signal.

5.What do you mean by process termination?

Process termination is a technique in which a process is terminated and release the CPU after completing the execution. Most of the OS use exit( ) system call to terminate a process. Main causes of process termination. 

6.What is despatcher?

The dispatcher is the module that gives control of the CPU to the process selected by the short-time scheduler(selects from among the processes that are ready to execute). The function involves : Switching context. Switching to user mode. Jumping to the proper location in the user program to restart that program7.Define safe state?

A state is safe if the system can allocate all resources requested by all processes ( up to their stated maximums ) without entering a deadlock state. ... If a safe sequence does not exist, then the system is in an unsafe state, which MAY lead to deadlock.

8.What is physical address?

A physical address is a binary number in the form of logical high and low states on an address bus that corresponds to a particular cell of primary storage(also called main memory), or to a particular register in a memory-mapped I/O(input/output) device.

9.Explain demand paging?

In virtual memory systems, demand paging is a type of swapping in which pages of data are not copied from disk to RAM until they are needed.

10.What is meant by page replacement?

The page replacement algorithm decides which memory page is to be replaced. The process of replacement is sometimes called swap out or write to disk. Page replacement is done when the requested page is not found in the main memory (page fault).

11.Define File?

            A file is an object on a computer that stores data, information, settings, or commands used with a computer program. In a GUI (graphical user interface), such as Microsoft Windows, files display as icons that relate to the program that opens the file.

12.What is meant by counting?

Counting numbers are the set of numbers that we use to learn how to count. 1, 2, 3, 4, 5, and so on. They are also called natural numbers—maybe since they feel natural to us because they are naturally the first numbers we learn. Sometimes they are also referred to as positive integers.

                                                                                                                        (10 X 2 = 20 marks)

Section B

Answer any 6 questions. Each question carries 5 marks.

13. Explain the services provided by the OS to the user?

• An operating system provides services to programs and to the users of those programs. It provides an environment for the execution of programs. The services provided by one operating system is different than other operating system.
• Operating system makes the programming task easier. The common services provided by the operating system is listed below.
• Program execution
• I/O operation
• File system manipulation
• Communications
• Error detection.

14. Write short notes on scheduling criteria?

·         Throughput. ...

·         Turnaround Time. ...

·         Waiting Time. ...

·         Load Average. ...

·         Response Time.

15. Explain priority queue scheduling with an example?

Priority scheduling is a method of scheduling processes based on priority. In this method, the scheduler chooses the tasks to work

 as per the priority, which is different from other types of scheduling, for example, a simple round robin.

16. What is a monitor? Briefly explain?

In concurrent programming, a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become true. ... A monitor consists of a mutex (lock) object and condition variables.

17.Discuss about the necessary conditions of a dead lock?

The resources involved must be unshareable; otherwise, the processes would not be prevented from using the resource when necessary. The processes must hold the resources they have already been allocated while waiting for other (requested) resources

18.Discuss about dead lock detection?

Deadlock detection is the process of actually determining that a deadlock exists and identifying the processes and resources involved in the deadlock.

19.Explain segmentation?

In Operating Systems, Segmentation is a memory management technique in which, the memory is divided into the variable size parts. Each part is known as segment which can be allocated to a process. The details about each segment are stored in a table called as segment table.

20. Explain dead lock avoidance?

Deadlock Avoidance. Deadlock avoidance merely works to avoid deadlock; it does not totally prevent it. The basic idea here is to allocate resources only if the resulting global state is a safe state. In other words, unsafe states are avoided, meaning that deadlock is avoided as well.

21.Explain FIFO and RR algorithms?

The simplest page-replacement algorithm is a FIFO algorithm . The first-in, first-out ( FIFO ) page replacement algorithm is a low-overhead algorithm that requires little bookkeeping on the part of the operating system. In simple words, on a page fault, the frame has been replaced by the longest one in memory.

Round-robin (RR) is one of the algorithms employed by process and network schedulers in computing. ... Round-robin scheduling can also be applied to other scheduling problems, such as data packet scheduling in computer networks. It is an operating system concept.

(6 X 5 = 30marks)

Section C

Answer any 2questions. It carries 15marks.

22.Explain the types of system calls?

  system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. ... System calls provide an essential interface between a process and the operating system.

23Briefly explain inter process communication?

Inter-process communication (IPC) is a mechanism that allows the exchange of data between processes. By providing a user with a set of programming interfaces, IPC helps a programmer organize the activities among different processes.

24.Explain dead lock prevention in details?

If a system is already in a safe state, we can try to stay away from an unsafe state and avoid deadlock. Deadlocks cannot be avoided in an unsafe state. ... A resource allocation graph is generally used to avoid deadlocks. If there are no cycles in the resource allocation graph, then there are no deadlocks.

25.Explain paging in detail?                                                                          

                        Paging is a method of writing data to, and reading it from, secondary storage for use in primary storage, also known as main memory. ... In a memory management system that takes advantage of paging, the OS reads data from secondary storage in blocks called pages, all of which have identical size.                                                                                              (2 X 15 = 30 marks)

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