## Operating-Systems

 Question 1
Consider a linear list based directory implementation in a file system. Each directory is a list of nodes, where each node contains the file name along with the file metadata, such as the list of pointers to the data blocks.Consider a given directory foo. Which of the following operations will necessarily require a full scan of foo for successful completion?
 A Deletion of an existing file from foo B Opening of an existing file in foo C Creation of a new file in foo D Renaming of an existing file in foo
Question 1 Explanation:
Renaming and creating a new file requires us to search the complete inode for duplicate names (to check if the same name already exists). There is no such problem in deleting and opening a file, as duplicate names are not possible while they are created.
 Question 2
There are 6 jobs with distinct difficulty levels, and 3 computers with distinct processing speeds. Each job is assigned to a computer such that:
• The fastest computer gets the toughest job and the slowest computer gets the easiest job.
• Every computer gets at least one job.
The number of ways in which this can be done is ______
 A 65
Question 2 Explanation:

Let the levels be  1,2,3,4,5,6. (1 is the least difficult, 6 is the most difficult level)
Let the computers be F,M,S( fast, medium, slow).

As per the given constraint,  1 must be given to F and 6 must be given to S.
Now we are left with 2,3,4,5 and  F being assigned 1, S being assigned 6 and M being assigned none.
Another constraint is that, every computer must be assigned atleast one.
So compute with assigning one job to M, two jobs to M, three jobs to M and four jobs to M.
Assigning one job to M: we can assign 1 out of 4 jobs in (4C1 ways) and remaining 3 jobs to F,S in  2*2*2 = 8  ways. (each job has two options, either F or S),

Assigning two jobs to M: we can select two jobs from 4 in 4C2 ways and remaining 2 can be distributed to  F and S in  2*2 ways ( each job has two options either F or S)

Assigning three jobs to M: we can select 3 out of 4 in 4C3 ways remaining can be distributed to F,M in 2 ways.

Assigning 4 jobs to M: it can be done in only one way.

Total : 4c1*8  +  4C2* 4  + 4C3*2 + 1

= 32+24+8+1

=65

 Question 3
Consider the following pseudocode, where S is a semaphore initialized to 5 in line#2 and counter is a shared variable initialized to 0 in line#1. Assume that the increment operation in line#7 is not atomic.
1. int counter = 0
2. Semaphore S = init(5);
3. void parop(void)
4. {
5.       wait(S);
6.       wait(S);
7.       counter++;
8.       signal(S);
9.       signal(S);
10. }
If five threads execute the function parop concurrently, which of the following program behaviour(s) is/are possible?
 A The value of counter is 1 after all the threads successfully complete the execution of parop. B The value of counter is 5 after all the threads successfully complete the execution of parop. C The value of counter is 0 after all the threads successfully complete the execution of parop. D There is a deadlock involving all the threads. E
Question 3 Explanation:

count =0

S=5

func()

{

wait();

wait();

count++;

signal();

signal();

}

No. of resources >= No. of process (Req-1) + 1

Here, no. of resources = 5 (semaphore value)

Each thread requires = 2 resources (wait call)

5 ≥ 5* (2-1)+1

≱ 6. So deadlock is possible.

This occurs when all 5 threads get blocked on first wait().

(2) count =5 is possible

When all threads enter CS and execute count++ sequentially.

(3) Count=1 is possible.

Assembly level:

inc R0, 1

write count, R0

MC R0, 1, so R0=1

Write R0 to count.

So, Count=1.

 Question 4
Which of the following standard C library functions will always invoke a system call when executed from a single-threaded process in a UNIX/linux operating system?
 A sleep B strlen C malloc D exit
Question 4 Explanation:
• A sleep system call takes a time value as a parameter, specifying the minimum amount of time that the process is to sleep before resuming execution. The parameter typically specifies seconds, although some operating systems provide finer resolution, such as milliseconds or microseconds.
• strlen() is not system call.
• The function call malloc() is a library function call that further uses the brk() or sbrk() system call for memory allocation
• Exit also system call
 Question 5
Three processes arrive at time zero with CPU bursts of 16, 20 and 10 milliseconds. If the scheduler has prior knowledge about the length of the CPU bursts, the minimum achievable average waiting time for these three processes in a non-preemptive scheduler (rounded to nearest integer) is _________ milliseconds.
 A 12
Question 5 Explanation:
Minimum average waiting time amongst non-preemptive scheduling is given by SJF. So, avg waiting time = (0+10+26)/3 = 12 ms.
 Question 6
In the context of operating systems, which of the following statements is/are correct with respect to paging?
 A Page size has no impact on internal fragmentation. B Multilevel paging is necessary to support pages of different sizes. C Paging incurs memory overheads. D Paging helps solve the issue of external fragmentation.
Question 6 Explanation:
1. False, Large page size may lead to higher internal fragmentation.
2. False, To support pages of different sizes, the Instruction set architecture should support it. Multi-level paging is not necessary.
3. True, The page table has to be stored in main memory, which is an overhead.
4. True, Paging avoids the external fragmentation.
 Question 7

Consider the resource allocation graph given in the figure.

(a) Find if the system is in a deadlock state. (b) Otherwise, find a safe sequence.

 A Theory Explanation.
 Question 8

Consider the following heap (figure) in which blank regions are not in use and hatched region are in use.

The sequence of requests for blocks of size 300, 25, 125, 50 can be satisfied if we use

 A either first fit or best fit policy (any one) B first fit but not best fit policy C best fit but first fit policy D None of the above
Question 8 Explanation:
In first fit, block request will be satisfied from the first free block that fits it.
So, request for 300 will be satisfied by 350 size block reducing the free size to 50.
Request for 25, satisfied by 125 size block, reducing it to 125.
Request for 125 satisfied by the 125 size block.
And request for 50 satisfied by 50 size block.
So, all requests can be satisfied.
In best fit strategy, a block request is satisfied by the smallest block in which can fit it. So, request for 300 will be satisfied by 350 size block reducing the free size to 50.
Request for 25, satisfied by 50 size block as its the smallest size that fits 25, reducing it to 25.
Request for 125, satisfied by 150 size block, reducing it to 25.
Now, request for 50 cannot be satisfied as the two 25 size blocks are not contiguous.
 Question 9

A memory page containing a heavily used variable that was initialized very early and is in constant use is removed when

 A LRU page replacement algorithm is used B FIFO page replacement algorithm is used C LFU page replacement algorithm is used D None of the above
Question 9 Explanation:
In FIFO, whichever comes first that can be removed first. If the variable was initialized very early, it is in set of first pages. So it was removed.
In LRU which can eliminate (or) removed which is least recently used.
In LFU the frequency of the page is more. So it is in constant use so cannot be replaced.
 Question 10

The head of a moving head disk with 100 tracks numbered 0 to 99 is currently serving a request at tract 55. If the queue of requests kept in FIFO order is

`  10, 70, 75, 23, 65 `

Which of the two disk scheduling algorithms FCFS (First Come First Served) and SSTF (Shortest Seek Time First) will require less head movement? Find the head movement for each of the algorithms.

 A Theory Explanation.
 Question 11

Consider the following program segment for concurrent processing using semaphore operators P and V for synchronization. Draw the precedence graph for the statements S1 to S9.

``` var
a, b, c, d, e, f, g, h, i, j, k : semaphore;
begin
cobegin
begin S1; V(a); V(b) end;
begin P(a); S2; V(c); V(d) end;
begin P(c); S4; V(c) end;
begin P(d); S5; V(f) end;
begin P(e); P(f); S7; V(k) end;
begin P(b); S3;V(g);V(h) end;
begin P(g); S6; V(i) end;
begin P(h); P(i); S8; V(j) end;
begin P(j); P(j); P(k); S9 end;
coend
end; ```
 A Theory Explanation.
 Question 12

A computer installation has 1000k of main memory. The jobs arrive and finish in the following sequences.

``` Job 1 requiring 200k arrives
Job 2 requiring 350k arrives
Job 3 requiring 300k arrives
Job 1 finishes
Job 4 requiring 120k arrives
Job 5 requiring 150k arrives
Job 6 requiring 80k arrives ```

(a) Draw the memory allocation table using Best Fit and First fit algorithms.
(b) Which algorithm performs better for this sequence?

 A Theory Explanation.
 Question 13

In a virtual memory system the address space specified by the address lines of the CUP must be __________ than the physical memory size and _______ than the secondary storage size.

 A smaller, smaller B smaller, larger C larger, smaller D larger, larger
Question 13 Explanation:
Primary memory < Virtual memory < Secondary memory.
 Question 14

The address sequence generated by tracing a particular program executing in a pure demand paging system with 100 records per page with 1 free main memory frame is recorded as follows. What is the number of page faults?

` 0100, 0200, 0430, 0499, 0510, 0530, 0560, 0120, 0220, 0240, 0260, 0320, 0370 `
 A 13 B 8 C 7 D 10
Question 14 Explanation:
Page are fitted in frames, so first we need to determine the pages but given request are just the record request in decimal. We can assume that first page to address from 0000 to 0099 and page 2 contains records from 0100 to 0199 and so on (it is given in question that each page contains 100 records) and so on. So page request string is
01, 02, 04, 04, 05, 05, 05, 01, 02, 02, 02, 03, 03.
Clearly 7 page faults.
 Question 15

The sequence …………… is an optimal non-preemptive scheduling sequence for the following jobs which leaves the CPU idle for …………… unit(s) of time.

 A {3,2,1),1 B (2,1,3},0 C {3,2,1),0 D {1,2,3},5
Question 15 Explanation:
Here, in option (B) and (C) they have given CPU idle time is 0 which is not possible as per schedule (B) and (C).
So, (B) and (C) will be eliminated.
Now in (A) and (D):
For r(A),

So, idle time is between 0 to 1 which in case of option (A).
For option(D),

We can see there is no idle time at all, but in option given idle time is 5, which is not matching with our chart. So option (D) is eliminated.
Therefore, the correct sequence is option (A).
 Question 16

Which scheduling policy is most suitable for a time shared operating system?

 A Shortest Job First B Round Robin C First Come First Serve D Elevator
Question 16 Explanation:
In Round robin, we use the time quantum based on this execution can be done. Then it is said to be time shared operating system.
 Question 17

Which of the following page replacement algorithms suffers from Belady’s anamoly?

 A Optimal replacement B LRU C FIFO D Both (A) and (C)
Question 17 Explanation:
FIFO is suffers from Belady's Anamoly.
 Question 18

In a paged segmented scheme of memory management, the segment table itself must have a page table because

 A the segment table is often too large to fit in one page B each segment is spread over a number of pages C segment tables point to page table and not to the physical locations of the segment D the processor’s description base register points to a page table E Both A and B
Question 18 Explanation:
The segment table is often too large to fit in one page. This is true and the segment table can be divided into pages. Thus page table for each segment table, pages are created.
Segment paging is different from paged segmentation.
 Question 19

Which of the following statements is true?

 A ROM is a Read/Write memory B PC points to the last instruction that was executed C Stack works on the principle of LIFO D All instructions affect the flags
Question 19 Explanation:
We know that stack works on the principle of LIFO.
 Question 20

Consider a paging system that uses a 1-level page table residing in main memory and a TLB for address translation. Each main memory access takes 100 ns and TLB lookup takes 20 ns. Each page transfer to/from the disk takes 5000 ns. Assume that the TLB hit ratio is 95%, page fault rate is 10%. Assume that for 20% of the total page faults, a dirty page has to be written back to disk before the required page is read in from disk. TLB update time is negligible. The average memory access time in ns (round off to 1 decimal places) is ______.

 A 154.5 ns
Question 20 Explanation:
M=100ns
T=20ns
D=5000ns
h=0.95
p=0.1, 1-p=0.9
d=0.2, 1-d=0.8
EMAT = h×(T+M)+(1-h)[(1-p)×2M+p[(1-d)[D+M]+d(2D+M)]+T]
= 0.95×(20+100)+(1-0.95)[(1-0.1)×200+(0.1)[(1-0.2)[5000+100]+(0.2)(10000+100)]+20]
= 154.5 ns
 Question 21

Consider the following five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time.

`         (P, 155), (Q, 85), (R, 110), (S, 30), (T, 115) `

Assume the head is positioned at cylinder 100. The scheduler follows Shortest Seek Time First scheduling to service the requests.

Which one of the following statements is FALSE?

 A The head reverses its direction of movement between servicing of Q and P. B T is serviced before P. C R is serviced before P. D Q is serviced after S, but before T.
Question 21 Explanation:
(P,155)(Q,85)(R,110)(S,30)(T,115)
 Question 22

Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.

```wait (a); count = count+1;
if (count==n) signal (b);
signal (a); wait (b); signal (b);```

What does the code achieve?

 A It ensures that all processes execute CODE SECTION P mutually exclusively. B It ensures that at most two processes are in CODE SECTION Q at any time. C It ensures that no process executes CODE SECTION Q before every process has finished CODE SECTION P. D It ensures that at most n-1 processes are in CODE SECTION P at any time.
Question 22 Explanation:
The wait(a) ensures that the count value is correctly incremented (no race condition) if(count==n) signal (b); // This signal(b) statement is executed by the last (nth) process only. Rest of the n-1 processes are blocked on wait(b). Once the nth process makes signal(b) then the rest of the processes can proceed and enter Code section Q.
 Question 23

Consider the following set of processes, assumed to have arrived at time 0. Consider the CPU scheduling algorithms Shortest Job First (SJF) and Round Robin (RR). For RR, assume that the processes are scheduled in the order P1,P2,P3,P4.

If the time quantum for RR is 4 ms, then the absolute value of the difference between the average turnaround times (in ms) of SJF and RR (round off to 2 decimal places) is _____.

 A 5.25
Question 23 Explanation:
SJF:

Turn Around Time = (21 – 0) + (13 – 0) + (2 – 0) + (6 – 0), Average = 42/4 = 10.50

Turn Around Time (TAT) = (18 – 0) + (21 – 0) + (10 – 0) + (14 – 0), Average = 63/4 = 15.75
Absolute difference = |10.50-15.75| = 5.25
 Question 24

Consider the following statements about process state transitions for a system using preemptive scheduling.

I. A running process can move to ready state.
II. A ready process can move to running state.
III. A blocked process can move to running state.
IV. A blocked process can move to ready state.

Which of the above statements are TRUE?

 A II and III only B I, II and III only C I, II, III and IV D I, II and IV only
Question 24 Explanation:
 Question 25

Consider allocation of memory to a new process. Assume that none of the existing holes in the memory will exactly fit the process’s memory requirement. Hence, a new hole of smaller size will be created if allocation is made in any of the existing holes. Which one of the following statements is TRUE?

 A The hole created by worst fit is always larger than the hole created by first fit. B The hole created by best fit is never larger than the hole created by first fit. C The hole created by first fit is always larger than the hole created by next fit. D The hole created by next fit is never larger than the hole created by best fit.
Question 25 Explanation:
The size of hole created using best fit is never greater than size created by first fit. The best fit chooses the smallest available partition to fit the size of the process. Whereas, first fit and next fit doesn’t consider the size of the holes available.
 Question 26

Consider the virtual page reference string

`1, 2, 3, 2, 4, 1, 3, 2, 4, 1  `

On a demand paged virtual memory system running on a computer system that main memory size of 3 pages frames which are initially empty. Let LRU, FIFO and OPTIMAL denote the number of page faults under the corresponding page replacements policy. Then

 A OPTIMAL < LRU < FIFO B OPTIMAL < FIFO < LRU C OPTIMAL = LRU D OPTIMAL = FIFO
Question 26 Explanation:
FIFO:

No. of page faults with FIFO = 6
LRU:

No. of page faults with LRU = 9
Optimal:

No. of page faults with optimal = 5
∴ Optimal < FIFO < LRU
 Question 27

A file system with 300 GByte disk uses a file descriptor with 8 direct block addresses, 1 indirect block address and 1 doubly indirect block address. The size of each disk block is 128 Bytes and the size of each disk block address is 8 Bytes. The maximum possible file size in this file system is

 A 3 KBytes B 35 KBytes C 280 KBytes D dependent on the size of the disk
Question 27 Explanation:
It’s given disk block is of size 128B.
So, one direct block addressing will point to 8 disk blocks = 8*128 B = 1 KB
Singly Indirect block addressing will point to 1 disk block which has 128/8 disc block addresses = (128/8)*128 B = 2 KB
Doubly indirect block addressing will point to 1 disk block which has 128/8 addresses to disk blocks which in turn has 128/8 addresses to disk blocks = 16*16*128 B = 32 KB
Maximum possible file size = 1 KB + 2 KB + 32 KB = 35 KB
 Question 28

Fetch_And_Add(X,i) is an atomic Read-Modify-Write instruction that reads the value of memory location X, increments it by the value i, and returns the old value of X. It is used in the pseudocode shown below to implement a busy-wait lock. L is an unsigned integer shared variable initialized to 0. The value of 0 corresponds to lock being available, while any non-zero value corresponds to the lock being not available.

```  AcquireLock(L){
L = 1;
}
ReleaseLock(L){
L = 0;
}```

This implementation

 A fails as L can overflow B fails as L can take on a non-zero value when the lock is actually available C works correctly but may starve some processes D works correctly without starvation
Question 28 Explanation:
Check the loop first:
L = 1; // A waiting process can be here just after
// the lock is released, and can make L = 1.
Assume P1 executes until while condition and preempts before executing L =1. Now P2 executes all statements, hence L = 0. Then P1 without checking L it makes L = 1 by executing the statement where it was preempted.
It takes a non-zero value (L=1) when the lock is actually available (L = 0). So option B.
 Question 29

Consider the 3 processes, P1, P2 and P3 shown in the table.

```Process           Arrival time         Time Units Required
P1                0                         5
P2                1                         7
P3                3                         4```

The completion order of the 3 processes under the policies FCFS and RR2 (round robin scheduling with CPU quantum of 2 time units) are

 A FCFS: P1, P2, P3 RR2: P1, P2, P3 B FCFS: P1, P3, P2 RR2: P1, P3, P2 C FCFS: P1, P2, P3 RR2: P1, P3, P2 D FCFS: P1, P3, P2 RR2: P1, P2, P3
Question 29 Explanation:
FCFS is - P1, P2, P3
FCFS is clear.
RR Queue: In RR queue time slot is of 2 units.
Processes are assigned in following order
P1, P2, P1, P3, P2, P1, P3, P2, P2
This question used the ready queue concept. At t=2, P2 starts and P1 is sent to the ready queue and at t=3 P3 arrives so then the job P3 is queued in the ready queue after P1. So at t=4, again P1 is executed then P3 is executed for the first time at t=6.
RR2: P1, P3, P2
So option C.
 Question 30

A process executes the code

```fork();
fork();
fork();```

The total number of child processes created is

 A 3 B 4 C 7 D 8
Question 30 Explanation:
The no. of child process created = 2n - 1 = 23 - 1 = 7 (where n is number of fork() statements)
7 are child processes.
 Question 31

A computer system uses the Banker’s Algorithm to deal with deadlocks. Its current state is shown in the table below, where P0, P1, P2 are processes, and R0, R1, R2 are resources types.

(a) Show that the system can be in this state.
(b) What will the system do on a request by process P0 for one unit of resource type R1?

 A Theory Explanation.
 Question 32

A file system with a one-level directory structure is implemented on a disk with disk block size of 4K bytes. The disk is used as follows:

``` Disk-block 0: File Allocation Table, consisting of one 8-bit entry per date block,
representing the data block address of the next date block in the file
Disk block 1: Directory, with one 32 bit entry per file:
Disk block 2: Data block 1;
Disk block 3: Data block 2; etc. ```

(a) What is the maximum possible number of files?
(b) What is the maximum possible file size in blocks?

 A Theory Explanation.
 Question 33

The concurrent programming constructs fork and join are as below:
fork

```   N = 2
M = 2
fork L3
fork L4
S1
L1:join N
S3
L2:join M
S5
L3:S2
goto L1
L4:S4
goto L2
next: ```
 A Theory Explanation.
 Question 34

A demand paged virtual memory system uses 16 bit virtual address, page size of 256 bytes, and has 1 Kbyte of main memory. LRU page replacement is implemented using a list whose current status (page number in decimal) is

` 00FF, 010D, 10FF, 11B0`

indicate
(i) the new status of the list
(ii) page faults, if any, and
(iii) page replacements, if any

 A Theory Explanation.
 Question 35

Four jobs to be executed on a single processor system arrive at time 0+ in the order A, B, C, D. their burst CPU time requirements are 4, 1, 8, 1 time units respectively. The completion time of A under round robin scheduling with time slice of one time unit is

 A 10 B 4 C 8 D 9
Question 35 Explanation:
Time quantum is 1 unit.

∴ Completion time of A is 9 unit.
 Question 36

The correct matching for the following pairs is

```         A. Activation record	   1. Linking loader
B. Location counter	   2. Garbage collection
C. Reference counts	   3. Subroutine call
D. Address relocation	   4. Assembler ```
 A A – 3 B – 4 C – 1 D – 2 B A – 4 B – 3 C – 1 D – 2 C A – 4 B – 3 C – 2 D – 1 D A – 3 B – 4 C – 2 D – 1
Question 36 Explanation:
Each time a subroutine is called its activation record is created.
An assembler uses location counter value to give address to each instruction which is needed for relative addressing as well as for jump labels.
Reference count is used by garbage collector to clear the memory whose reference count be comes 0.
Linker loader is a loader which can load several compiled codes and link them together into a single executable. Thus it needs to do relocation of the object codes.
 Question 37

A solution to the Dining Philosophers Problem which avoids deadlock is

 A ensure that all philosophers pick up the left fork before the right fork B ensure that all philosophers pick up the right fork before the left fork C ensure that one particular philosopher picks up the left fork before the right fork, and that all other philosophers pick up the right fork before the left fork D None of the above
Question 37 Explanation:
In the Dining philosopher problem, each philosopher needs exactly two chopsticks to eat food but the problem is: each philosopher is going to take one chopstick at a time, which is placed at its right-hand side or at its left-hand side, but remember all should choose in the same manner like if first one chooses in a clockwise manner then each one should choose in clockwise, this type of picking cause, a circular waiting loop because each one is depending on other. This is also called as circular waiting and it leads to deadlock.
To avoid this, atleast one philosopher should choose its first chopstick in different way so that circular loop is not formed.
 Question 38

A 1000 Kbyte memory is managed using variable partitions but to compaction. It currently has two partitions of sizes 200 Kbytes and 260 Kbytes respectively. The smallest allocation request in Kbytes that could be denied is for

 A 151 B 181 C 231 D 541
Question 38 Explanation:
200 and 260 are already hold by some other processes. Now we have to model the partition in such a way so that smallest allocation request could be denied. So, we can do the division as,

So, smallest allocation request which can be denied is 181 KB.
 Question 39

A critical section is a program segment

 A which should run in a certain specified amount of time B which avoids deadlocks C where shared resources are accessed D which must be enclosed by a pair of semaphore operations, P and V
Question 39 Explanation:
In CS, share resources are accessed.
 Question 40

Which of the following is an example of spooled device?

 A A line printer used to print the output of a number of jobs. B A terminal used to enter input data to a running program. C A secondary storage device in a virtual memory system. D A graphic display device.
Question 40 Explanation:
Example of spooled device is a line printer used to print the output of a number of jobs.
 Question 41

The process state transition diagram in below figure is representative of

 A a batch operating system B an operating system with a preemptive scheduler C an operating system with a non-preemptive scheduler D a uni-programmed operating system
Question 41 Explanation:
Transaction from running → ready present.
So this is preemptive.
 Question 42

Each Process Pi, i = 1.......9 is coded as follows

```    repeat
P(mutex)
{Critical section}
V(mutex)
forever   ```

The code for P10 is identical except it uses V(mutex) in place of P(mutex). What is the largest number of processes that can be inside the critical section at any moment?

 A 1 B 2 C 3 D None of the above
Question 42 Explanation:
Since the both code (i.e., P1 to P9 and P10) can be executed any number of times and code for P10 is
repeat
{
V(mutex)
C.S.
V(mutex)
}
forever
Now, let me say P1 is in CS then P1 is in CS
then P10 comes and executes CS (upon mutex).
Now, P2 comes (down on mutex).
Now P10 moves out of CS (again binary semaphore will be 1).
Now P3 comes (down on mutex).
Now P10 comes (upon mutex).
Now P4 comes (down mutex).

So, if we take P10 'in' and 'out' of CS recursively, all 10 processes can be in CS at same time using binary semaphore only.
 Question 43

An operating system contains 3 user processes each requiring 2 units of resource R. The minimum number of units of r such that no deadlocks will ever arise is

 A 3 B 5 C 4 D 6
Question 43 Explanation:
For the system to cause deadlock give each process 1 resource less than they require. Since in this case they require 2 resource each, so just give them 1 resource each. So if at max if 3 resource will be available then there can be deadlock. So by adding one more resource deadlock will never occur. So in total minimum 4 resources are required so that deadlock will never occur.
 Question 44

I/O redirection

 A implies changing the name of a file B can be employed to use an existing file as input file for a program C implies connection 2 programs through a pipe D None of the above
Question 44 Explanation:
Redirection is known as capturing output from a file, command, program (or) even code block within a script and sending it as input to another file, command, program (or) script.
 Question 45

Thrashing

 A reduces page I/O B decreases the degree of multiprogramming C implies excessive page I/O D improve the system performance
Question 45 Explanation:
Thrashing implies excessive page I/O.
 Question 46

Dirty bit for a page in a page table

 A helps avoid unnecessary writes on a paging device B helps maintain LRU information C allows only read on a page D None of the above
Question 46 Explanation:
The dirty bit allows for a performance optimization i.e., Dirty bit for a page in a page table helps to avoid unnecessary writes on a paging device.
 Question 47

Locality of reference implies that the page reference being made by a process

 A will always be to the page used in the previous page reference B is likely to be to one of the pages used in the last few page references C will always be to one of the pages existing in memory D will always lead to a page fault
Question 47 Explanation:
Locality of reference is also called as principle of locality. There are three different principle of locality:
(1) Temporal locality
(2) Spatial locality
(3) Sequential locality
→ In programs related data are stored in consecutive locations and loops in same locations are used repeatedly.
 Question 48

The correct matching for the following pairs is

```(A) Disk Scheduling        (1) Round robin
(B) Batch Processing       (2) SCAN
(C) Time sharing           (3) LIFO
(D) Interrupt processing   (4) FIFO  ```
 A A – 3 B – 4 C – 2 D – 1 B A – 4 B – 3 C – 2 D – 1 C A – 2 B – 4 C – 1 D – 3 D A – 3 B – 4 C – 3 D – 2
Question 48 Explanation:
Disk scheduling - SCAN
Batch processing - FIFO
Time sharing - Round Robin
Interrupt processing - LIFO
 Question 49

(a) Free disk space can be kept track of using a free list or a bit map. Disk addresses require d bits. For a disk with 13 blocks, F of which is free, state the condition under which the free list uses less space than the bit map.

(b) Consider a disk with C cylinders, t tracks per cylinder, s sectors per track and a sector length sl. A logical file dl with fixed record length rl is stored continuously on this disk starting at location (cL,tL,sL), where cL, tL and SL are the cylinder, track and sector numbers, respectively. Derive the formula to calculate the disk address (i.e. cylinder, track and sector) of a logical record n assuming that rl=sl.

 A Theory Explanation.
 Question 50

Consider n processes sharing the CPU in a round-robin fashion. Assuming that each process switch takes s seconds, what must be the quantum size q such that the overhead resulting from process switching is minimized but at the same time each process is guaranteed to get its turn at the CPU at least every t seconds?

 A q ≤ t-ns/n-1 B q ≥ t-ns/n-1 C q ≤ t-ns/n+1 D q ≥ t-ns/n+1
Question 50 Explanation:
There are 50 questions to complete.

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