# Operating System

 Question 1
Consider a computer system with 57-bit virtual addressing using multi-level tree-structured page tables with L levels for virtual to physical address translation. The page size is 4 KB (1 KB = 1024 B) and a page table entry at any of the levels occupies 8 bytes.
The value of L is ______.
 A 4 B 5 C 6 D 7
GATE CSE 2023      Memory Management
Question 1 Explanation:
 Question 2
Consider the following two-dimensional array D in the C programming language, which is stored in row-major order:

int D[128][128];

Demand paging is used for allocating memory and each physical page frame holds 512 elements of the array D. The Least Recently Used (LRU) page-replacement policy is used by the operating system. A total of 30 physical page frames are allocated to a process which executes the following code snippet:

for (int i = 0; i < 128; i++)
for (int j = 0; j < 128; j++)
D[j][i] *= 10;


The number of page faults generated during the execution of this code snippet is _____.
 A 128 B 4096 C 1024 D 2048
GATE CSE 2023      Memory Management
Question 2 Explanation:

 Question 3
Consider the two functions incr and decr shown below.

incr(){
wait(s);
X = X+1;
signal(s);
}

decr(){
wait(s);
X = X-1;
signal(s);
}


There are 5 threads each invoking incr once, and 3 threads each invoking decr once, on the same shared variable X. The initial value of X is 10.
Suppose there are two implementations of the semaphore $s$, as follows:

I-1: s is a binary semaphore initialized to 1.
I-2: s is a counting semaphore initialized to 2.

Let V1, V2 be the values of X at the end of execution of all the threads with implementations I-1, I-2, respectively.
Which one of the following choices corresponds to the minimum possible values of V1, V2, respectively?
 A 15, 7 B 7, 7 C 12, 7 D 12, 8
GATE CSE 2023      Process Synchronization
Question 3 Explanation:
 Question 4
Which one or more of the following CPU scheduling algorithms can potentially cause starvation?
 A First-in First-Out B Round Robin C Priority Scheduling D Shortest Job First
GATE CSE 2023      CPU Scheduling
Question 4 Explanation:
 Question 5
Which one or more of the following options guarantee that a computer system will transition from user mode to kernel mode?
 A Function Call B malloc Call C Page Fault D System Call
GATE CSE 2023      System Call
Question 5 Explanation:

There are 5 questions to complete.

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1. CORRECT THE QUESTION 355