Code: AC-13                                                                            Subject: OPERATING SYSTEMS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

a. Windows 2000 OS can act as a  

(A)  Web client.                                   (B)  Web server.

(C)   Both (A) & (B).                           (D)  Neither (A) nor (B).

             b.   While executing OS instructions the processor works in   

(A) Privileged mode.                           (B)  User mode.

(C) Dual mode.                                   (D)  Network mode.         

             c.   The Application Programming Interface (API) contains  

(A) Network protocols.                      (B)  System calls.

(C)  Error detection codes                   (D)  Encryption data.

             d.   ‘Fork’ leads to a

(A)  Interrupt.                                      (B)  Exception.

(C)  Child process.                              (D)  Suspend process.

             e.   ‘Wait’ and ‘Signal’ primitives belong to   

(A)  Semaphores.                                (B)  Queues.

(C)  Mailboxes.                                   (D)  Pipes.

             f.   The optimum CPU scheduling algorithm is

(A) FIFO.                                           (B) SJF with preemption.

                   (C) SJF without preemption.                (D) Round Robin.

     g.   Bankers algorithm is used in  

(A) Deadlock detection.                      (B)  Deadlock prevention.

                   (C) Deadlock avoidance.                     (D)  Inter process synchronisation.

             h.   A paging system with 8 pages and 1024 words each in these pages has ______ bits in its logical address.

(A) 15 bits                                           (B)  20 bits

                   (C) 10 bits                                           (D)  13 bits

i.    Belady’s anamoly refers to     

(A)  Page fault variation.                     

(B)  Loss of synchrony between processes.

                   (C)  Misbehaviour of child processes.

                   (D)  None of the above.

             j.    ‘Cycle stealing’ is found in

(A) Virtual memory.                             (B)  DMA access.

                   (C) RAM accesses.                             (D)  Segmentation.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   What are the advantages of multiprogramming?                                                   (6)

b.   With a neat diagram, describe the storage device hierarchy of a computing system.              (10)

Q.3     a.   Describe the virtual machine architecture of an OS.  What are its advantages from the user view point and system view point?                               (10)

             b.   Write a small code fragment each for the producer process and the consumer process.                   (6)

Q.4     a.   Describe in brief, the various issues involved in multithreading.                             (8)

b.   Given the following set of processes with the length of CPU Burst time given in milliseconds: Apply FCFS, SJF pre-emptive and SJF non preemptive and Round Robin scheduling algorithms to estimate the turnaround time for each of the processes:             (8)

Process	Burst time	Priority
	10	3
	1	1
	2	3
	1	4
	5	2

Q.5     a.   Using simple constructs write the ‘Wait’ and ‘Signal’ primitives of a Counting Semaphore using those of a Binary Semaphore.                              (6)

             b.   What are the necessary conditions for a deadlock to occur?  What is the role of Resource Allocation graph in a deadlock situation?                        (10)

  Q.6     a.   Consider a paging system with the page table stored in memory.  If a memory reference takes  what is the effective access time for a memory reference using a TLB with 75% hit rate and 50 access time?  What is the % improvement in access time using a TLB?                                     (6)

             b.   Describe the virtual memory scheme in Windows NT and Solaris2 operating systems.                     (10)

Q.7     a.   What are the methods adopted for free space management on a disk?               (10)

             b.   Describe the hardware and software aspects of the kernel I/O subsystem.           (6)

Q.8     a.   Define the following w.r.t. disk scheduling:

(i)    Seek time                                     (ii)  Rotational Latency

                   (iii)  Bandwidth                                    (iv) Constant linear velocity

                   (v)   Constant angular velocity              (vi)  Mapping                                          (6)

b. What are the design issues that challenge a distributed system designer?            (10)

Q.9     a.   Compare the stateful and stateless services.                                                        (6)

b.   What are the user threats, program threats and system threats to the data in a computer system?  Is there a common solution to all the three?          (10)