Solution for Operating System

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1 Solution for Operating System May 2016 Index Q.1) a). 2 b). 3 c).3-5 d).5-7 Q.2) a) b) Q.3) a) b) Q.4) a). N.A b). N.A Q.5) a) b). N.A Q.6) a). 26 b) c). N.A d)

2 Q1.Attempt All a) What is mutual exclusion? Explain its Significance. (05) Ans :- Mutual Exclusion :- Mutual Exclusion Condition :- 2

3 b) Discuss various scheduling Criteria. (05) Ans :- Scheduling Criteria c) Explain services provided by operating system. (05) Ans :- operating System Services 3

4 1) User Interface 2) I/O operations 3) Communications 4) Program executions 5) File System Manipulation 6) Error Detection 4

5 d) Write short notes on system calls. (05) Ans :- System Calls 5

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8 Q2. a) What is deadlock? Explain the necessary and sufficient conditions for the deadlock. Suggest techniques to avoid deadlock. (10) Ans :- Deadlock Problem We know that processes needs different resources in order to complete the execution. So in a multiprogramming environment, many process may compete for a multiple number of resources. In a system, resources are finite. So with finite number of resources, it is not possible to fulfil the resource request of all processes. When a process request a resource and if the resource is not available that time, the process enters await state. In a multiprogramming environment it may happen with many processes. There is chance that waiting process will remain in same state and will never again change state. It is because the resources they have requested are held by other waiting processes. When such type of situation occurs then it is called as deadlock. The allocation of any instance of the resources type will satisfy the request of the process if it requests the instance of the resource. If it will not, then the instance are not identical, and the resource type classes have not been defined properly. 8

9 Deadlock Avoidance :- 9

10 Disk drives are available in the system. Finally P2 can be allocated all the needed disk drives and returns the after completion. (The system will have now all 10 disk drives available). Figure shows safe, unsafe and deadlock state spaces. 10

11 At time t1, if any process requests the additional resource say disk drives in our example and if after allocation other process could not be allocated needed resource type due to unavailability, then system may go in unsafe state. 1) Deadlock Avoidance Algorithm :- a) Resource-Allocation graph Algorithm b) Banker s Algorithm c) Resources-Request Algorithm d) Safety Algorithm a) Resource-Allocation graph Algorithm :- If system has resources allocation system with only one instance of each resource, type, then only this algorithm is applicable. Claim edge (dotted edg e) in resources allocation graph is like a future request edge When a process requests a resources, the claim edge is converted to a request edge. When a process release a resource, the assignment edge Is converted to a claim edge. 11

12 b) Bankers Algorithm :- c) Resources-Request Algorithm :- 12

13 d) Safety Algorithm :- 13

14 b) Differentiate the following : 1) Process vs Thread Ans :- Process and Threads 14

15 2) Preemptive vs Non-Preemptive Scheduling Ans :- 15

16 Q3. a) Explain the following in brief : 1) Process Synchronisation Ans :- Synchronization 16

17 17

18 2) Inter-Process Communication (IPC) Ans :- The process executing concurrently in the system may be either independent process or cooperative process. A process is independent if it cann ot effect or be affected by the other processes executing in the system. Any process that doesn t share data with any other process is independent. A process is cooperative of it can affect or be affected by the other process executing in the system. Any process that shares data with any other process is a cooperating process.there are following reasons for inter process communication. 1) Information sharing: Since several users may be interested in the same piece of information, we must provide an environment to allow the concurrent access to such information. 2) Commutation speed up: If we want a particular task to run faster,we must break it into subtask, each of which will be executing in parallel with the other 3) Modularity: We may want to construct a system in a modular fashion dividing a system function into separate process or threads. 4) Convenience: A user may work on many tasks at same time.for instance a user may be editing, printing and compiling in parallel. It should be easy for the user to perform multiple at the same time. Cooperative process require an IPCs that will allow them to exchange data and information.there are two fundamentals modules in IPCs. 1) Shared memory 2) Message passing In the shared memory module, a region of memory that is shared by cooperating process is established.process can then exchange information by reading and writing data to the shared region. In message passing model communication take place by means of message exchanged between the cooperative processes. Message passing is useful for exchanging smaller amount of data and it is also easier to implement than shared memory for inter computer communication (ICC) Shared memory allows maximum speed an convenience of communication as it can be done at memory speed when within a computer. Shared memory is faster than message passing as message passing system are implemented using system calls In shared memory system, system calls are required only to establish shared memory region.once it is established all access are treated as routine memory access and no assistance from kernel is required. 18

19 b) Discuss partition selection algorithm in brief. Given memory partition of 150k, 500k, 200k, 300k, & 550k (in order), how would each of the first fit, best fit and worst fit algorithm place the processes of 220k, 430k, 110k, & 425k (in order). Which algorithm makes the most efficient use of memory? (10) Ans :- Contiguous Memory Location 19

20 Q4. a) Find AWT, ATAT, ART and AWTAT f or the following set of processes with CPU burst time in ms. Assume that all processes arrive at time 0. (P1-19), (P2-7), (P3-3) i) FCFS with order P2,P3,P1 ii) Round Robin (Quantum 2ms) Ans :- N. A. b) Explain paging hardware with TLB along with protection bits in page table. Ans :- N.A. Q5. a) Explain various allocation methods with reference to file system? Ans :- Implementing Files 20

21 1)Contiguous Allocation :- 21

22 2)Linked List Allocation 22

23 3)Linked list Allocation Using a Table in a Memory 23

24 4)Indexed Allocation 24

25 5) I-nodes 25

26 b) Calculate hit and miss percentage for the following string using page replacement policies FIFO, LRU and Optimal. Compare it for the frame size 3 and 4. Ans :- N.A. 26

27 Q6. Write short notes for the following : a) File management in Linux Ans :- 27

28 Ans :- b) Belady s anomaly Using FIFO algorithm for some reference strings actually generate more page faults when more page frames are allocated.this truly unexpected result was first demonstrated by Belady in 1970 and is known as Belady s anomaly FIFO does not satisfy the inclusion property and is not a stack of algorithm. A page replacement algorithm that satisfies the inclusion property is free from Belady s anomaly. Consider the reference string : 1,2,3,4,1,2,5,1,2,3,5. Page frame size =3 Refernece String Page frame 1 Page frame 2 Page frame Page fault PF PF PF PF PF PF PF PF Total number of page faults = 9 Page frame size =4 Refernece String Page frame 1 Page frame 2 Page frame Page fault PF PF PF PF PF PF PF PF PF Total number of pages fault =

29 Paging algorithm has worse performance when the amount of primary memory allocated in the process is increased.the problem creates because the set of page loaded with a memory allocation of 3 is not same as that with the memory allocation of 4 There are set of demand paging algorithm whereby the set of pages loaded with an allocation of m frames Is always a subset of a set of page loaded with an allocation m+ 1 frame. This property is called the inclusion property. FIFO does not satisfy the inclusion property and is not a stack algorithm It suffers from Belayd s anomaly. c) Case study of windows operating system Ans :- Ans :- d) Virtual memory Demanding Page 29

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MC7204 OPERATING SYSTEMS

MC7204 OPERATING SYSTEMS QUESTION BANK UNIT I INTRODUCTION 9 Introduction Types of operating systems operating systems structures Systems components operating systems services System calls Systems programs