# Computer Science: Gate 2007 Paper

WWW.ONESTOPGATE.COM
Q.1 – Q.20 Carry One Mark Each
1. Consider the following two statements about the function f (x )= x :
P. f (x) is continuous for all real values of x
Q. f (x) is differentiable for all real values of x
Which of the following is TRUE?
(A) P is true and Q is false. (B) P is false and Q is true.
(C) Both P and Q are true. (D) Both P and Q are false.
2. Let S be a set of n elements. The number of ordered pairs in the largest and the
smallest equivalence relations on S are:
(A) n and n (B) 2 n and n (C) 2 n and 0 (D) n and 1
3. What is the maximum number of different Boolean functions involving n Boolean
variables?
(A) 2 n (B) 2n (C) 2 2
n
(D)
2
2n
4. Let G be the non-planar graph with the minimum possible number of edges. Then
G has
(A) 9 edges and 5 vertices (B) 9 edges and 6 vertices
(C) 10 edges and 5 vertices (D) 10 edges and 6 vertices
5. Consider the DAG with V = {1,2,3,4,5,6}, shown below.
Which of the following is NOT a topological ordering?
(A) 1 2 3 4 5 6 (B) 1 3 2 4 5 6 (C) 1 3 2 4 6 5 (D) 3 2 4 1 6 5
6. Which of the following problems is undecidable?
(A) Membership problem for CFGs. (B) Ambiguity problem for CFGs.
(C) Finiteness problem for FSAs. (D) Equivalence problem for FSAs.
2 5
1
3
4
6
½CS½Computer Science: Gate 2007 Paper
http://www.onestopgate.com
Page 1
WWW.ONESTOPGATE.COM
7. Which of the following is TRUE?
(A) Every subset of a regular set is regular.
(B) Every finite subset of a non-regular set is regular.
(C) The union of two non-regular sets is not regular.
(D) Infinite union of finite sets is regular.
8. How many 3-to-8 line decoders with an enable input are needed to construct a 6-
to-64 line decoder without using any other logic gates?
(A) 7 (B) 8 (C) 9 (D) 10
9. Consider the following Boolean function of four variables:
f (w,x,y ,z ) =  (1,3,4,6,9,11,12,14)
The function is:
(A) independent of one variables. (B) independent of two variables.
(C) independent of three variables. (D) dependent on all the variables.
10. Consider a 4-way set associative cache consisting of 128 lines with a line size of
64 words. The CPU generates a 20-bit address of a word in main memory. The
number of bits in the TAG, LINE and WORD fields are respectively:
(A) 9, 6, 5 (B) 7, 7, 6 (C) 7, 5, 8 (D) 9, 5, 6
11. Consider a disk pack with 16 surfaces, 128 tracks per surface and 256 sectors
per track. 512 bytes of data are stored in a bit serial manner in a sector. The
capacity of the disk pack and the number of bits required to specify a particular
sector in the disk are respectively:
(A) 256 Mbyte, 19 bits (B) 256 Mbyte, 28 bits
(C) 512 Mbyte, 20 bits (D) 64 Gbyte, 28 bits
12. The height of a binary tree is the maximum number of edges in any root to leaf
path. The maximum number of nodes in a binary tree of height h is:
(A) 2 1 h − (B) 1 2 1 h− − (C) 1 2 1 h+ − (D) 1 2h+
13. The maximum number of binary trees that can be formed with three unlabeled
nodes is:
(A) 1 (B) 5 (C) 4 (D) 3
14. Which of the following sorting algorithms has the lowest worst-case complexity?
(A) Merge sort (B) Bubble sort (C) Quick sort (D) Selection sort
½CS½Computer Science: Gate 2007 Paper
http://www.onestopgate.com
Page 2
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
15. Consider the following segment of C-code:
int j, n;
j = 1;
while (j <=n)
j = j*2;
The number of comparisons made in the execution of the loop for any n > 0 is:
(A) log2 n + 1 (B) n (C) 2 log n (D) 2 log n + 1
16. Group 1 contains some CPU scheduling algorithms and Group 2 contains some
applications. Match entries in Group 1 to entries in Group 2.
(A) P – 3 Q – 2 R – 1 (B) P – 1 Q – 2 R – 3
(C) P – 2 Q – 3 R – 1 (D) P – 1 Q – 3 R – 2
17. Consider the following statements about user level threads and kernel level
threads. Which one of the following statements is FALSE?
(A) Context switch time is longer for kernel level threads than for user level
(B) User level threads do not need any hardware support.
(C) Related kernel level threads can be scheduled on different processors in a
multi-processor system.
18. Which one of the following is a top-down parser?
(A) Recursive descent parser. (B) Operator precedence parser.
(C) An LR(k) parser. (D) An LALR(k) parser.
19. In Ethernet when Manchester encoding is used, the bit rate is:
(A) Half the baud rate. (B) Twice the baud rate.
(C) Same as the baud rate. (D) None of the above
20. Which one of the following uses UDP as the transport protocol?
(A) HTTP (B) Telnet (C) DNS (D) SMTP
Group I Group II
(P) Gang Scheduling (1) Guaranteed Scheduling
(Q) Rate Monotonic Scheduling (2) Real-time Scheduling
(R) Fair Share Scheduling (3) Thread Scheduling
http://www.onestopgate.com
Page 3
WWW.ONESTOPGATE.COM
Q.21 – Q.75 Carry Two Marks Each
21. How many different non-isomorphic Abelian groups of order 4 are there?
(A) 2 (B) 3 (C) 4 (D) 5
22. Let Graph(x) be a predicate which denotes that x is a graph. Let Connected(x) be
a predicate which denotes that x is connected. Which of the following first order
logic sentences DOES NOT represent the statement: “Not every graph is
connected”?
(A) ¬”x (Graph (x) Connected (x)) (B) \$x (Graph (x) Ù ¬Connected (x))
(C) ¬”x (¬Graph (x) Ú Connected (x)) (D) “x (Graph (x)  ¬Connected (x))
23. Which of the following graphs has an Eulerian circuit?
(A) Any k-regular graph where k is an even number.
(B) A complete graph on 90 vertices.
(C) The complement of a cycle on 25 vertices.
(D) None of the above
24. Suppose we uniformly and randomly select a permutation from the 20!
Permutations of 1, 2,3 ,…..,20. What is the probability that 2 appears at an
earlier position than any other even number in the selected permutation?
(A)
1
2
(B)
1
10
(C)
9!
20!
(D) None of these
25. Let A be a 4 × 4 matrix with eigenvalues -5, -2, 1, 4. Which of the following is an
eigenvalue of ,
A I
I A
 
 
 
where I is the 4 × 4 identity matrix?
(A) -5 (B) -7 (C) 2 (D) 1
26. Consider the set S = {a,b,c,d}. Consider the following 4 partitions 1 2 3 4 p ,p ,p ,p on
{ } { } { } { } 1 2 3 4 S :p = abcd ,p = ab,cd ,p = abc,d ,p = a,b,c,d . Let p be the partial
order on the set of partitions { } 1 2 3 4 S¢ = p ,p ,p ,p defined as follows: i j p p p if and
only if i
p refines . j p The poset diagram for (S¢, ) p is:
(A) (B)
1 p
2 p
3 p
4 p
1 p
2 p
3 p
4 p
½CS½Computer Science: Gate 2007 Paper
http://www.onestopgate.com
Page 4
WWW.ONESTOPGATE.COM
(C) (D)
27. Consider the set of (column) vectors defined by
{ 3 }
1 2 3 1 2 3 0, where , , .
T T X = x Î R x + x + x = x = x x x  Which of the following is
TRUE?
(A) {1, 1,0 , 1,0, 1 }
T T  −   −  is a basis for the subspace X.
(B) {1, 1,0 , 1,0, 1 }
T T  −   −  is a linearly independent set, but it does not span X and
therefore is not a basis of X.
(C) X is not a subspace of 3 R
(D) None of the above
28. Consider the series 1 0
9
, 0.5
2 8
n
n
n
x
x x
x
+ = + = obtained from the Newton-Raphson
method. The series converges to
(A) 1.5 (B) 2 (C) 1.6 (D) 1.4
29. A minimum state deterministic finite automaton accepting the language
{ { }* }
L = w w Î 0,1 , number of 0s and 1s in w are divisible by 3 and 5, respectively
has
(A) 15 states (B) 11 states (C) 10 states (D) 9 states
30. The language {0 21 0} i i L = i ³ over the alphabet {0,1,2} is:
(A) not recursive
(B) is recursive and is a deterministic CFL.
(C) is a regular language.
(D) is not a deterministic CFL but a CFL.
1 p
2 p
4 p
3 p
3 p
2 p
1 p
4 p
½CS½Computer Science: Gate 2007 Paper
http://www.onestopgate.com
Page 5
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
31. Which of the following languages is regular?
(A) { {0,1} } R ww w
+ Î (B) { , {0,1} } R ww x x w
+ Î
(C) { , {0,1} } R wxw x w
+ Î (D) { , {0,1} } R xww x w
+ Î
32. Let f (w, x, y, z) = (0,4,5,7,8,9,13,15). Which of the following expressions are
NOT equivalent to f ?
(P) x¢y¢z¢ + w¢xy¢ + wy¢z + xz
(Q) w¢y¢z¢ + wx¢y¢ + xz
(R) w¢y¢z¢ + wx¢y¢ + xyz + xy¢z
(S) x¢y¢z¢ + wx¢y¢ + w¢y
(A) P only (B) Q and S (C) R and S (D) S only
33. Define the connective * for the Boolean variables X and Y as: X * Y = XY + X¢Y ¢.
Let Z = X *Y. Consider the following expressions P, Q and R.
p P : X = Y * Z Q :Y = X * Z R : X *Y * Z = 1
Which of the following is TRUE?
(A) Only P and Q are valid. (B) Only Q and R are valid.
(C) Only P and R are valid. (D) All P, Q, R are valid.
34. Suppose only one multiplexer and one inverter are allowed to be used to
implement any Boolean function of n variables. What is the minimum size of the
multiplexer needed?
(A) 2n line to 1 line (B) 1 2n+ line to 1 line
(C) 1 2n− line to 1 line (D) 2 2n− line to 1 line
35. In a look-ahead carry generator, the carry generate function i G and the carry
propagate function i P for inputs i A and i B are given by:
and i i i i i i P = A Å B G = A B
The expressions for the sum bit i S and the carry bit i 1 C + of the look-ahead carry
1 0 and , where is the input carry. i i i i i i i S = P Å C C + = G + PC C
Consider a two-level logic implementation of the look-ahead carry generator.
Assume that all i and G i P are available for the carry generator circuit and that
the AND and OR gates can have any number of inputs. The number of AND gates
and OR gates needed to implement the look-ahead carry generator for a 4-bit
adder with 3 2 1 0 4 S ,S ,S ,S and C as its outputs are respectively:
(A) 6, 3 (B) 10, 4 (C) 6, 4 (D) 10, 5
http://www.onestopgate.com
Page 6
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
36. The control signal functions of a 4-bit binary counter are given below (where X is
“don’t care”):
1 X X X Clear to 0
0 X 0 0 No change
0 ­ 1 X Load input
0 ­ 0 1 Count next
The counter is connected as follows:
Assume that the counter and gate delays are negligible. If the counter starts at
0, then it cycles through the following sequence:
(A) 0, 3, 4 (B) 0, 3, 4, 5
(C) 0, 1, 2, 3, 4 (D) 0, 1, 2, 3, 4, 5
37. Consider a pipelined processor with the following four stages:
IF: Instruction Fetch
ID: Instruction Decode and Operand Fetch
EX: Execute
WB: Write Back
The IF, ID and WB stages take one clock cycle each to complete the operation.
The number of clock cycles for the EX stage depends on the instruction. The ADD
and SUB instructions need 1 clock cycle and the MUL instruction needs 3 clock
cycles in the EX stage. Operand forwarding is used in the pipelined processor.
What is the number of clock cycles taken to complete the following sequence of
instructions?
ADD R2, R1, R0 R2  R1 + R0
MUL R4, R3, R2 R4  R3 * R2
SUB R6, R5, R4 R6  R5 − R4
Clear
Inputs
0 0 1 1
4-bit counter
4 A 3 A 2 A 1 A
Count=1
Clock
http://www.onestopgate.com
Page 7
WWW.ONESTOPGATE.COM
(A) 7 (B) 8 (C) 10 (D) 14
38. The following postfix expression with single digit operands is evaluated using a
stack:
8 2 3 Ù / 2 3 * + 5 1 * –
Note that Ù is the exponentiation operator. The top two elements of the stack
after the first * is evaluated are:
(A) 6, 1 (B) 5, 7 (C) 3, 2 (D) 1, 5
39. The inorder and preorder traversal of a binary tree are
d b e a f c g and a b d e c f g, respectively
The postorder traversal of the binary tree is:
(A) d e b f g c a (B) e d b g f c a (C) e d b f g c a (D) d e f g b c a
40. Consider a hash table of size seven, with starting index zero, and a hash function
(3x + 4)mod7. Assuming the hash table is initially empty, which of the following
is the contents of the table when the sequence 1, 3, 8, 10 is inserted into the
table using closed hashing? Note that − denotes an empty location in the table.
(A) 8, −, −, −, −, −, 10 (B) 1, 8, 10, −, −, −, 3
(C) 1, −, −, −, −, −, 3 (D) 1, 10, 8, −, −, −, 3
41. In an unweighted, undirected connected graph, the shortest path from a node S
to every other node is computed most efficiently, in terms of time complexity, by
(A) Dijkstra’s algorithm starting from S.
(B) Warshall’s algorithm
(C) Performing a DFS starting from S.
(D) Performing a BFS starting from S.
42. Consider the following C function:
int f(int n)
{static int r = 0;
if (n <= 0) return 1;
if (n > 3)
{r = n;
return f(n-2)+2;
}
return f(n-1)+r;
}
What is the value of f (5)?
(A) 5 (B) 7 (C) 9 (D) 18
½CS½Computer Science: Gate 2007 Paper
http://www.onestopgate.com
Page 8
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
43. A complete n-ary tree is a tree in which each node has n children or no children.
Let I be the number of internal nodes and L be the number of leaves in a
complete n-ary tree. If L = 41, and I = 10, what is the value of n?
(A) 3 (B) 4 (C) 5 (D) 6
44. In the following C function, let n ³ m.
int gcd(n,m)
{
if (n%m ==0) return m;
n = n%m;
return gcd(m,n);
}
How many recursive calls are made by this function?
(A) Q (log2 n ) (B) W(n) (C) ( ) 2 2 Q log log n (D) Q ( n)
45. What is the time complexity of the following recursive function:
int DoSomething (int n) {
if (n <= 2)
return 1;
else
return (DoSomething (floor(sqrt(n))) + n);
}
(A) ( 2 ) Q n (B) ( ) 2 Q nlog n (C) ( ) 2 Q log n (D) ( ) 2 2 Q log log n
46. Consider the following C program segment where CellNode represents a node in a
binary tree:
struct CellNode {
struct CellNOde *leftChild;
int element;
struct CellNode *rightChild;
};
int GetValue (struct CellNode *ptr) {
int value = 0;
if (ptr != NULL) {
if ((ptr->leftChild == NULL) &&
(ptr->rightChild == NULL))
value = 1;
else
value = value + GetValue(ptr->leftChild)
http://www.onestopgate.com
Page 9
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
+ GetValue(ptr->rightChild);
}
return(value);
}
The value returned by GetValue when a pointer to the root of a binary tree is
passed as its argument is:
(A) the number of nodes in the tree
(B) the number of internal nodes in the tree
(C) the number of leaf nodes in the tree
(D) the height of the tree
47. Consider the process of inserting an element into a Max Heap, where the Max
Heap is represented by an array. Suppose we perform a binary search on the
path from the new leaf to the root to find the position for the newly inserted
element, the number of comparisons performed is:
(A) Q (log2 n ) (B) ( ) 2 2 Q log log n (C) Q (n) (D) ( ) 2 Q nlog n
48. Which of the following is TRUE about formulae in Conjunctive Normal Form?
(A) For any formula, there is a truth assignment for which at least half the
clauses evaluate to true.
(B) For any formula, there is a truth assignment for which all the clauses
evaluate to true.
(C) There is a formula such that for each truth assignment, at most one-fourth of
the clauses evaluate to true.
(D) None of the above.
49. Let w be the minimum weight among all edge weights in an undirected connected
graph. Let e be a specific edge of weight w . Which of the following is FALSE?
(A) There is a minimum spanning tree containing e.
(B) If e is not in a minimum spanning tree T, then in the cycle formed by adding
e to T, all edges have the same weight.
(C) Every minimum spanning tree has an edge of weight w .
(D) e is present in every minimum spanning tree.
50. An array of n numbers is given, where n is an even number. The maximum as
well as the minimum of these n numbers needs to be determined. Which of the
following is TRUE about the number of comparisons needed?
(A) At least 2n − c comparisons, for some constant c, are needed.
(B) At most 1.5n − 2 comparisons are needed.
(C) At least 2 nlog n comparisons are needed.
(D) None of the above.
http://www.onestopgate.com
Page 10
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
51. Consider the following C code segment:
int IsPrime(n)
{
int i,n;
for(i=2;i<=sqrt(n);i++)
if(n%i == 0)
{printf(“Not Prime\n”); return 0;}
return 1;
}
Let T (n)denote the number of times the for loop is executed by the program on
input n. Which of the following is TRUE?
(A) T (n) = O( n) and T (n) = W( n) (B) T (n) = O( n) and T (n) = W(1)
(C) T (n) = O(n) and T (n) = W( n) (D) None of the above
52. Consider the grammar with non-terminals { } 1 N = S,C,S , terminals
T = {a,b, i, t,e}, with S as the start symbol, and the following set of rules:
1
1
S iCtSS a
S eS
C b
e
®
®
®
The grammar is NOT LL(1) because:
(A) it is left recursive (B) it is right recursive
(C) it is ambiguous (D) it is not context-free.
53. Consider the following two statements:
P: Every regular grammar is LL(1)
Q: Every regular set has a LR(1) grammar
Which of the following is TRUE?
(A) Both P and Q are true (B) P is true and Q is false
(C) P is false and Q is true (D) Both P and Q are false
54. In a simplified computer the instructions are:
j OP R , i R – Performs j i R OP R and stores the result in register . i R
OP m, i R – Performs val i OP R and stores the result in . i R val
denotes the content of memory location m.
MOV , i m R – Moves the content of memory location m to register . i R
MOV , i R m – Moves the content of register i R to memory location m.
The computer has only to registers, and OP is either ADD or SUB. Consider the
following basic block:
http://www.onestopgate.com
Page 11
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
1
2
3 2
4 1 3
t a b
t c d
t e t
t t t
= +
= +
= −
= −
Assume that all operands are initially in memory. The final value of the
computation should be in memory. What is the minimum number of MOV
instructions in the code generated for this basic block?
(A) 2 (B) 3 (C) 5 (D) 6
55. An operating system uses Shortest Remaining Time first (SRT) process
scheduling algorithm. Consider the arrival times and execution times for the
following processes:
Process Execution time Arrival time
P1 20 0
P2 25 15
P3 10 30
P4 15 45
What is the total waiting time for process P2?
(A) 5 (B) 15 (C) 40 (D) 55
56. A virtual memory system uses First In First Out (FIFO) page replacement policy
and allocates a fixed number of frames to a process. Consider the following
statements:
P: Increasing the number of page frames allocated to a process sometimes
increases the page fault rate.
Q: Some programs do not exhibit locality of reference.
Which one of the following is TRUE?
(A) Both P and Q are true, and Q is the reason for P
(B) Both P and Q are true, but Q is not the reason for P.
(C) P is false, but Q is true
(D) Both P and Q are false.
57. A single processor system has three resource types X, Y and Z, which are shared
by three processes. There are 5 units of each resource type. Consider the
following scenario, where the column alloc denotes the number of units of each
resource type allocated to each process, and the column request denotes the
number of units of each resource type requested by a process in order to
complete execution. Which of these processes will finish LAST?
http://www.onestopgate.com
Page 12
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
(A) P0 (B) P1 (C) P2
(D) None of the above, since the system is in a deadlock.
58. Two processes, P1 and P2, need to access a critical section of code. Consider the
following synchronization construct used by the processes:
Here, wants1 and wants2 are shared variables, which are initialized to false.
Which one of the following statements is TRUE about the above construct?
(A) It does not ensure mutual exclusion.
(B) It does not ensure bounded waiting.
(C) It requires that processes enter the critical section in strict alternation.
(D) It does not prevent deadlocks, but ensures mutual exclusion.
59. Information about a collection of students is given by the relation
studinfo(studId, name, sex). The relation enroll(studId, courseId) gives which
student has enrolled for (or taken) what course(s). Assume that every course is
taken by at least one male and at least one female student. What does the
following relational algebra expression represent?
(( ( ( )) ( )) ) courseId studId “female” courseId studInfo enroll enroll sex P P s = × P −
(A) Courses in which all the female students are enrolled.
(B) Courses in which a proper subset of female students are enrolled.
(C) Courses in which only male students are enrolled.
(D) None of the above
alloc request
X Y Z X Y Z
P0 1 2 1 1 0 3
P1 2 0 1 0 1 2
P2 2 2 1 1 2 0
/* P1 */
while (true) {
wants1 = true;
while (wants2==true);
/* Critical
Section */
wants1=false;
}
/* Remainder section */
/* P2 */
while (true) {
wants2 = true;
while (wants1==true);
/* Critical
Section */
Wants2=false;
}
/* Remainder section */
http://www.onestopgate.com
Page 13
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
60. Consider the relation employee(name, sex, supervisorName) with name as the
key. supervisorName gives the name of the supervisor of the employee under
consideration. What does the following Tuple Relational Calculus query produce?
{e.name employee (e )Ù}
(“x) ¬employee (x) Ú x.supervisorName ¹ e.name Ú x.sex = “male” }
(A) Names of employees with a male supervisor.
(B) Names of employees with no immediate male subordinates.
(C) Names of employees with no immediate female subordinates.
(D) Names of employees with a female supervisor.
61. Consider the table employee(empId, name, department, salary) and the two
queries 1 2 Q ,Q below. Assuming that department 5 has more than one employee,
and we want to find the employees who get higher salary than anyone in the
department 5, which one of the statements is TRUE for any arbitrary employee
table?
1 Q : Select e.empId
From employee e
Where not exists
(Select * From employee s where s.department = “5” and s.salary >=e.salary)
2 Q : Select e.empId
From employee e
Where e.salary > Any
(Select distinct salary From employee s Where s.department = “5”)
(A) 1 Q is the correct query
(B) 2 Q is the correct query
(C) Both 1 2 Q and Q produce the same answer.
(D) Neither 1 2 Q nor Q is the correct query
62. Which one of the following statements if FALSE?
(A) Any relation with two attributes is in BCNF
(B) A relation in which every key has only one attribute is in 2NF
(C) A prime attribute can be transitively dependent on a key in a 3 NF relation.
(D) A prime attribute can be transitively dependent on a key in a BCNF relation.
63. The order of a leaf node in a B tree + − is the maximum number of (value, data
record pointer) pairs it can hold. Given that the block size is 1K bytes, data
record pointer is 7 bytes long, the value field is 9 bytes long and a block pointer
is 6 bytes long, what is the order of the leaf node?
(A) 63 (B) 64 (C) 67 (D) 68
http://www.onestopgate.com
Page 14
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
64. Consider the following schedules involving two transactions. Which one of the
following statements is TRUE?
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
1 1 1 2 2 2 1
2 1 2 2 2 1 1
: ; ; ; ; ;
: ; ; ; ; ;
S r X r Y r X r Y w Y w X
S r X r X r Y w Y r Y w X
(A) Both S1 and S2 are conflict serializable.
(B) 1 S is conflict serializable and 2 S is not conflict serializable.
(C) 1 S is not conflict serializable and 2 S is conflict serializable.
(D) Both 1 2 S and S are not conflict serializable.
65. There are n stations in a slotted LAN. Each station attempts to transmit with a
probability p in each time slot. What is the probability that ONLY one station
transmits in a given time slot?
(A) ( ) 1
1
n
np p
− − (B) ( ) 1
1
n
p
− − (C) ( ) 1
1
n
p p
− − (D) ( ) 1
1 1
n
p
− − −
66. In a token ring network the transmission speed is 7 10 bps and the propagation
speed is 200 metres/Rs. The 1-bit delay in this network is equivalent to:
(A) 500 metres of cable. (B) 200 metres of cable.
(C) 20 metres of cable. (D) 50 metres of cable.
67. The address of a class B host is to be split into subnets with a 6-bit subnet
number. What is the maximum number of subnets and the maximum number of
hosts in each subnet?
(A) 62 subnets and 262142 hosts. (B) 64 subnets and 262142 hosts.
(C) 62 subnets and 1022 hosts. (D) 64 subnets and 1024 hosts.
68. The message 11001001 is to be transmitted using the CRC polynomial 3 x + 1 to
protect it from errors. The message that should be transmitted is:
(A) 11001001000 (B) 11001001011
(C) 11001010 (D) 110010010011
69. The distance between two stations M and N is L kilometers. All frames are K bits
long. The propagation delay per kilometer is t seconds. Let R bits/second be the
channel capacity. Assuming that processing delay is negligible, the minimum
number of bits for the sequence number field in a frame for maximum utilization,
when the sliding window protocol is used, is:
(A) 2
2 2
log
LtR K
K
 + 
 
 
(B) 2
2
log
LtR
K
 
 
 
(C) 2
2
log
LtR K
K
 + 
 
 
(D) 2
2
log
2
LtR K
K
 + 
 
 
http://www.onestopgate.com
Page 15
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
70. Match the following:
(P) SMTP (1) Application layer
(Q) BGP (2) Transport layer
(R) TCP (3) Data link layer
(S) PPP (4) Network layer
(5) Physical layer
(A) P – 2 Q – 1 R – 3 S – 5
(B) P – 1 Q – 4 R – 2 S – 3
(C) P – 1 Q – 4 R – 2 S – 5
(D) P – 2 Q – 4 R – 1 S – 3
Common Data Questions
Common Data for Questions 71, 72, 73:
Consider the following program segment. Here R1, R2 and R3 are the general purpose
registers.
Instruction Operation Instruction size (no.of words)
MOV R1, (3000) R1  m[3000] 2
LOOP: MOV R2, (R3) R2  M[R3] 1
ADD R2, R1 R2  R1 + R2 1
MOV (R3), R2 M[R3]  R2 1
INC R3 R3  R3 + 1 1
DEC R1 R1  R1 – 1 1
BNZ LOOP Branch on not zero 2
HALT Stop 1
Assume that the content of memory location 3000 is 10 and the content of the register
R3 is 2000. The content of each of the memory locations from 2000 to 2010 is 100. The
program is loaded from the memory location 1000. All the numbers are in decimal.
71. Assume that the memory is word addressable. The number of memory references
for accessing the data in executing the program completely is:
(A) 10 (B) 11 (C) 20 (D) 21
72. Assume that the memory is word addressable. After the execution of this
program, the content of memory location 2010 is:
(A) 100 (B) 101 (C) 102 (D) 110
http://www.onestopgate.com
Page 16
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
73. Assume that the memory is byte addressable and the word size is 32 bits. If an
interrupt occurs during the execution of the instruction “INC R3”, what return
address will be pushed on to the stack?
(A) 1005 (B) 1020 (C) 1024 (D) 1040
Common Data for Questions 74, 75:
Consider the following Finite State Automaton:
74. The language accepted by this automaton is given by the regular expression
(A) * * * * b ab ab ab (B) ( )*
a + b (C) ( )* * b a a + b (D) * * * b ab ab
75. The minimum state automaton equivalent to the above FSA has the following
number of states
(A) 1 (B) 2 (C) 3 (D) 4
Suppose the letters a, b, c, d, e, f have probabilities
1 1 1 1 1 1
, , , , , ,
2 4 8 16 32 32
respectively.
76. Which of the following is the Huffman code for the letter a, b, c, d, e, f?
(A) 0, 10, 110, 1110, 11110, 11111
(B) 11, 10, 011, 010, 001, 000
(C) 11, 10, 01, 001, 0001, 0000
(D) 110, 100, 010, 000, 001, 111
77. What is the average length of the correct answer to Q.76?
(A) 3 (B) 2.1875 (C) 2.25 (D) 1.9375
Consider the CFG with {S, A,B} as the non-terminal alphabet, {a,b}as the terminal
alphabet, S as the start symbol and the following set of production rules:
a
q0 q1
q2
b b
a
a
q3
a
b
b
http://www.onestopgate.com
Page 17
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
S aB S bA
B b A a
B bS A aS
B aBB S bAA
® ®
® ®
® ®
® ®
78. Which of the following strings is generated by the grammar?
(A) aaaabb (B) aabbbb (C) aabbab (D) abbbba
79. For the correct answer strings to Q.78, how many derivation trees are there?
(A) 1 (B) 2 (C) 3 (D) 4
Consider a machine with a byte addressable main memory of 16 2 bytes. Assume that a
direct mapped data cache consisting of 32 lines of 64 bytes each is used in the system.
A 50 × 50 two-dimensional array of bytes is stored in the main memory starting from
memory location 1100H. Assume that the data cache is initially empty. The complete
array is accessed twice. Assume that the contents of the data cache do not change in
between the two accesses.
80. How many data cache misses will occur in total?
(A) 48 (B) 50 (C) 56 (D) 59
81. Which of the following lines of the data cache will be replaced by new blocks in
accessing the array for the second time?
(A) line 4 to line 11 (B) line 4 to line 12
(C) line 0 to line 7 (D) line 0 to line 8
A process has been allocated 3 page frames. Assume that none of the pages of the
process are available in the memory initially. The process makes the following sequence
of page references (reference string): 1, 2, 1, 3, 7, 4, 5, 6, 3, 1
82. If optimal page replacement policy is used, how many page faults occur for the
above reference string?
(A) 7 (B) 8 (C) 9 (D) 10
83. Least Recently Used (LRU) page replacement policy is a practical approximation
to optimal page replacement. For the above reference string, how many more
page faults occur with LRU than with the optimal page replacement policy?
(A) 0 (B) 1 (C) 2 (D) 3
http://www.onestopgate.com
Page 18
WWW.ONESTOPGATE.COM
½CS½Computer Science: Gate 2007 Paper
Suppose that a robot is placed on the Cartesian plane. At each step it is allowed to move
either one unit up or one unit right, i.e., if it is at (i, j ) then it can move to either
(i + 1, j ) or (i, j + 1).
84. How many distinct paths are there for the robot to reach the point (10,10)
starting from the initial position (0,0)?
(A)
20
10


(B) 20 2
(C) 10 2 (D) None of the above
85. Suppose that the robot is not allowed to traverse the line segment from (4,4) to
(5,4). With this constraint, how many distinct paths are there for the robot to
reach (10,10) starting from (0,0)?
(A) 9 2 (B) 19 2
(C)
8 11
4 5

×



(D)
20 8 11
10 4 5

− ×




http://www.onestopgate.com
Page 19