GATE CS Operating System questions

A computer uses $46\text{-bit}$ virtual address, $32\text{-bit}$ physical address, and a three–level paged page table organization. The page table base register stores the base address of the first-level table $\text{(T1)}$, which occupies exactly one page. Each entry of $\text{T1}$ stores the base address of a page of the second-level table …

Consider the virtual page reference string $$\text{1, 2, 3, 2, 4, 1, 3, 2, 4, 1}$$ on a demand paged virtual memory system running on a computer system that has main memory size of $3$ page frames which are initially empty. Let $\text{LRU}$, $\text{FIFO}$ and $\text{OPTIMAL}$ denote the number of page faults under the corresponding page replacement …

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

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 …

Consider the $3$ processes, $P1, P2$ and $P3$ shown in the table. $$\small \begin{array}{|c|c|c|} \hline \textbf{Process} & \textbf{Arrival Time} & \textbf{Time Units Required} \\ \hline \text{P1} & 0 & 5\\ \hline \text{P2} & 1 & 7 \\ \hline \text{P3} & 3 & 4 \\ \hline \end{array}$$The completion order of the $3$ …

A process executes the code fork(); fork(); fork(); The total number of child processes created is

An application loads $100$ libraries at startup. Loading each library requires exactly one disk access. The seek time of the disk to a random location is given as $10$ ms. Rotational speed of disk is $6000$ rpm. If all $100$ libraries are loaded from random locations on the disk, how long does it take to load all libraries? (The time to transfer data …

Let the page fault service time be $10$ milliseconds(ms) in a computer with average memory access time being $20$ nanoseconds (ns). If one page fault is generated every $10^6$ memory accesses, what is the effective access time for memory?

A thread is usually defined as a "light weight process" because an Operating System (OS) maintains smaller data structure for a thread than for a process. In relation to this, which of the following statement is TRUE?

A computer handles several interrupt sources of which of the following are relevant for this question. Interrupt from CPU temperature sensor (raises interrupt if CPU temperature is too high) Interrupt from Mouse (raises Interrupt if the mouse is moved or a button is pressed) Interrupt from Keyboard (raises Interrupt if a key is pressed or released) Interrupt …

Let the time taken to switch from user mode to kernel mode of execution be $T1$ while time taken to switch between two user processes be $T2$. Which of the following is correct?

A system has $n$ resources $R_0, \dots,R_{n-1}$, and $k$ processes $P_0, \dots, P_{k-1}$. The implementation of the resource request logic of each process $P_i$ is as follows: $\text{if} (i\%2==0) \{$ $\quad\text{if} (i<n) \text{ request } R_i;$ $\quad\text{if} (i+2 < n) \text{ request } R_{i+2}; \}$ $\text{else} \{$ …

The following program consists of $3$ concurrent processes and $3$ binary semaphores. The semaphores are initialized as $S0=1, S1=0$ and $S2=0.$ …

Which of the following statements are true? Shortest remaining time first scheduling may cause starvation Preemptive scheduling may cause starvation Round robin is better than FCFS in terms of response time

A system uses FIFO policy for system replacement. It has $4$ page frames with no pages loaded to begin with. The system first accesses $100$ distinct pages in some order and then accesses the same $100$ pages but now in the reverse order. How many page faults will occur?

Consider the methods used by processes $P1$ and $P2$ for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables $S1$ and $S2$ are randomly assigned. …

A hard disk has $63$ sectors per track, $10$ platters each with $2$ recording surfaces and $1000$ cylinders. The address of a sector is given as a triple $\langle c, h, s \rangle$, where $c$ is the cylinder number, $h$ is the surface number and $s$ is the sector number. Thus, the 0$^{th}$ sector is addresses as $\langle 0, 0, 0 \rangle$, …

A hard disk has $63$ sectors per track, $10$ platters each with $2$ recording surfaces and $1000$ cylinders. The address of a sector is given as a triple $\langle c, h, s \rangle$, where $c$ is the cylinder number, $h$ is the surface number and $s$ is the sector number. Thus, the 0$^{th}$ sector is addresses as $\langle 0, 0, 0 \rangle$, …

A multilevel page table is preferred in comparison to a single level page table for translating virtual address to physical address because

The enter_CS() and leave_CS() functions to implement critical section of a process are realized using test-and-set instruction as follows: void enter_CS(X) { while(test-and-set(X)); } void leave_CS(X) { X = 0; } In the above solution, $X$ is a memory location associated with the $CS$ and is initialized to $0$. Now consider the following statements: The …