GATE-CS-2004 (original) (raw)

Consider two processes P1 and P2 accessing the shared variables X and Y protected by two binary semaphores SX and SY respectively, both initialized to 1. P and V denote the usual semaphore operators, where P decrements the semaphore value, and V increments the semaphore value. The pseudo-code of P1 and P2 is as follows : P1 :

While true do {
L1 : ................
L2 : ................
X = X + 1;
Y = Y - 1;
V(SX);
V(SY);
}

P2 :

While true do {
L3 : ................
L4 : ................
Y = Y + 1;
X = Y - 1;
V(SY);
V(SX);
}

In order to avoid deadlock, the correct operators at L1, L2, L3 and L4 are respectively

• P(SY), P(SX); P(SX), P(SY)
• P(SX), P(SY); P(SY), P(SX)
• P(SX), P(SX); P(SY), P(SY)
• P(SX), P(SY); P(SX), P(SY)

A and B are the only two stations on an Ethernet. Each has a steady queue of frames to send. Both A and B attempt to transmit a frame, collide, and A wins the first backoff race. At the end of this successful transmission by A, both A and B attempt to transmit and collide. The probability that A wins the second backoff race is:

How many 8-bit characters can be transmitted per second over a 9600 baud serial communication link using asynchronous mode of transmission with one start bit, eight data bits, two stop bits, and one parity bit ?

Assume that the operators +, -, × are left associative and ^ is right associative. The order of precedence (from highest to lowest) is ^, x , +, -. The postfix expression corresponding to the infix expression a + b × c - d ^ e ^ f is

The recurrence equation

T(1) = 1 T(n) = 2T(n - 1) + n, n ≥ 2

evaluates to

**a). 2 n + 1 - n - 2
**b). 2 n - n
**c). 2 n + 1 - 2n - 2
**d. 2 n + n

Let A[1, ..., n] be an array storing a bit (1 or 0) at each location, and f(m) is a function whose time complexity is θ(m). Consider the following program fragment written in a C like language:

C `

counter = 0; for (i = 1; i < = n; i++) { if (A[i] == 1) counter++; else { f(counter); counter = 0; } }

`

The complexity of this program fragment is

Two matrices M1 and M2 are to be stored in arrays A and B respectively. Each array can be stored either in row-major or column-major order in contiguous memory locations. The time complexity of an algorithm to compute M1 × M2 will be

• best if A is in row-major, and B is in column- major order
• best if both are in row-major order
• best if both are in column-major order
• independent of the storage scheme

Consider a system with a two-level paging scheme in which a regular memory access takes 150 nanoseconds, and servicing a page fault takes 8 milliseconds. An average instruction takes 100 nanoseconds of CPU time, and two memory accesses. The TLB hit ratio is 90%, and the page fault rate is one in every 10,000 instructions. What is the effective average instruction execution time?

The minimum number of page frames that must be allocated to a running process in a virtual memory environment is determined by

• the instruction set architecture
• number of processes in memory

Consider the following C function

C `

void swap (int a, int b) { int temp; temp = a; a = b; b = temp; }

`

In order to exchange the values of two variables x and y.

• swap(x,y) cannot be used as it does not return any value
• swap(x,y) cannot be used as the parameters are passed by value

There are 90 questions to complete.

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