Q. There are three processes P1, P2 and P3 sharing a semaphore for synchronising a variable. Initial value of semaphore is one. Assume that negative value of semaphore tells us how many processes are waiting in queue. Processes access the semaphore in following order:

(a) P2 needs to access
(b) P1 needs to access
(c) P3 needs to access
(d) P2 exits critical section
(e) Pi exits critical section

The final value of semaphore will be:

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Q. In a paging system, it takes 30 ns to search translation Look-aside Buffer (TLB) and 90 ns to access the main memory. If the TLB hit ratio is 70%, the effective memory access time is:

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Q. Match the following w.r.t. Input/Output management:

List-l List-II
a. Device controller i. Extracts information from the controller register and store it in data buffer
b. Device driver ii. I/O scheduling
c. Interrupt handler iii. Performs data transfer
d. Kernel I/O subsystem iv. Processing of I/O request

Codes: a b c d

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Q. Which of the following scheduling algorithms may cause starvation?
a. First-come-first-served
b. Round Robin
c. Priority
d. Shortest process next
e. Shortest remaining time first

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Q. Distributed operating systems consist of:

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Q. Which of the following is incorrect for virtual memory

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Q. Consider following schedules involving two transactions:

S1: r1(X); r1(Y); r2(X); r2(Y); w2(Y); w1(X)
S2: r1(X); r2(X); r2(Y); w2(Y); r1(Y); w1(X)

Which of the following statement is true?

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Q. A memory management system has 64 pages with 512 bytes page size. Physical memory consists of 32 page frames. Number of bits required in logical and physical address are respectively:

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Q. Consider a disk queue with I/O requests on the following cylinders in their arriving order:

6,10,12,54,97,73,128,15,44,110,34,45

The disk head is assumed to be at cylinder 23 and moving in the direction of decreasing number of cylinders. Total number of cylinders in the disk is 150. The disk head movement using SCAN-scheduling algorithm is:

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Q. Match the following for Unix rue system:

List-I                  List-II
a. Boot block     i. Information about file system,
free block list, free inode list etc.
b. Super block ii. Contains operating system files
as well as program and data files
created by users.
c. Inode block   iii. Contains boot program and
partition table.
d. Data block    iv. Contains a table for every file in
the file system. Attributes of files
are stored here.

Codes:
     a   b  c   d

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Q. Some of the criteria for calculation of priority of a process are:

a. Processor utilization by an individual process.
b. Weight assigned to a user or group of users.
c. Processor utilization by a user or group of processes.

In fair share scheduler, priority is calculated based on:

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Q. One of the disadvantages of user level threads compared to Kernel level threads is

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Q. Names of some of the Operating Systems are given below:

(a) MS-DOS
(b) XENIX
(c) OS/2

In the above list, following operating systems didn’t provide multiuser facility.

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Q. Consider a system with seven processes A through G and six resources R through W.
Resource ownership is as follows:

process A holds R and wants T
process B holds nothing but wants T
process C holds nothing but wants S
process D holds U and wants S & T
process E holds T and wants V
process F holds W and wants S
process G holds V and wants U

Is the system deadlocked ? If yes, ............. processes are deadlocked.

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Q. Suppose that the virtual Address space has eight pages and physical memory with four page frames. If LRU page replacement algorithm is used, .............. number of page faults occur with the reference string.

0 2 1 3 5 4 6 3 7 4 7 3 3 5 5 3 1 1 1 7 2 3 4 1

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Q. Consider a system having ‘m’ resources of the same type. These resources are shared by three processes P1, P2 and P3 which have peak demands of 2, 5 and 7 resources respectively. For what value of ‘m’ deadlock will not occur?

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Q. Five jobs A, B, C, D and E are waiting in Ready Queue. Their expected runtimes are 9, 6, 3, 5 and x respectively. All jobs entered in Ready queue at time zero. They must run in ............. order to minimize average response time if 3 < x < 5.

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Q. Consider three CPU intensive processes P1, P2, P3 which require 20, 10 and 30 units of time, arrive at times 1, 3 and 7 respectively. Suppose operating system is implementing Shortest Remaining Time first (pre-emptive scheduling) algorithm, then .............. context switches are required (suppose context switch at the beginning of Ready queue and at the end of Ready queue are not counted).

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Q. Consider a system which have ‘n’ number of processes and ‘m’ number of resource types. The time complexity of the safety algorithm, which checks whether a system is in safe state or not, is of the order of:

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Q. An operating system supports a paged virtual memory, using a central processor with a cycle time of one microsecond. It costs an additional one microsecond to access a page other than the current one. Pages have 1000 words, and the paging device is a drum that rotates at 3000 revolutions per minute and transfers one million words per second. Further, one percent of all instructions executed accessed a page other than the current page. The instruction that accessed another page, 80% accessed a page already in memory and when a new page was required, the replaced page was modified 50% of the time. What is the effective access time on this system, assuming that the system is running only one process and the processor is idle during drum transfers ?

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