# Recent questions and answers in Operating System

1
Three CPU-bound tasks, with execution times of $15,12$ and $5$ time units respectively arrive at times $0,t$ and $8$, respectively. If the operating system implements a shortest remaining time first scheduling algorithm, what should be the value of $t$ to have $4$ context switches? Ignore the context switches at time $0$ and at the end. $0<t<3$ $t=0$ $t<=3$ $3<t<8$
1 vote
2
Jobs keep arriving at a processor. A job can have an associated time length as well as a priority tag. New jobs may arrive while some earlier jobs are running. Some jobs may keep running indefinitely. A ... the following job-scheduling policies is starvation free? Round - robin Shortest job first Priority queuing Latest job first None of the others
3
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$P_1, P_2, P_3, P_4$ ... absolute value of the difference between the average turnaround times (in ms) of SJF and RR (round off to $2$ decimal places is_______
4
Consider the following five disk 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 ... $S$,but before $T$. The head reverses its direction of movement between servicing of $Q$ and $P$. $R$ is serviced before $P$.
5
Consider the following statements about process state transitions for a system using preemptive scheduling. A running process can move to ready state. A ready process can move to running state. A blocked process can move to running state. A blocked process can move to ready state. Which of the above statements are TRUE? I, II, and III only II and III only I, II, and IV only I, II, III and IV only
6
Names of some of the Operating Systems are given below: MS-DOS XENIX OS/$2$ In the above list, following operating systems didn’t provide multiuser facility. (a) only (a) and (b)only (b) and (c) only (a),(b) and (c)
7
Which statements is not correct about “init” process in Unix? It is generally the parent of the login shell. It has PID $1$. It is the first process in the system. Init forks and execs a ‘getty’ process at every port connected to a terminal.
8
Consider three CPU-intensive processes, which require $10,20$ and $30$ time units and arrive at times $0,2$ and $6$, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end. $1$ $2$ $3$ $4$
9
Consider three processes, all arriving at time zero, with total execution time of $10,20$ and $30$ units, respectively. Each process spends the first $20\%$ of execution time doing I/O, the next $70\%$ of time doing computation, and the last $10\%$ of time doing I/O again. The ... as much as possible. For what percentage of time does the CPU remain idle? $0\%$ $10.6\%$ $30.0\%$ $89.4\%$
10
Determine the number of page faults when references to pages occur in the following order: $1,2,4,5,2,1,2,4$. Assume that the main memory can accommodate $3$ pages and the main memory already has the pages $1$ and $2$, with page $1$ having been brought earlier than page $2$.(LRU algorithm is used). $3$ $5$ $4$ None of these.
1 vote
11
Operating System maintains the page table for : each process each thread each instruction each address
12
If a processor has $32$-bit virtual address, $28$-bit physical address, $2$ kb pages. How many bits are required for the virtual, physical page number? $17,21$ $21,17$ $6,10$ None
1 vote
13
Assuming that the system call $\text{fork}()$ never fails, consider the following C program $P1$ and $P2$ ... Both Statement $I$ and Statement $II$ are false Statement $I$ is correct but Statement $II$ is false Statement $I$ is incorrect but Statement $II$ is true
14
Suppose you have a Linux file system where the block size is $2K$ bytes, a disk address is $32$ bits, and an $i-$node contains the disk addresses of the first $12$ direct blocks of file, a single indirect block and a double indirect block. Approximately, what is the largest file that can be represented by an $i-$node? $513$ Kbytes $513$ MBytes $537$ Mbytes $537$ KBytes
15
Consider a disk system having $60$ cylinders. Disk requests are received by a disk drive for cylinders $10,22,20,2,40,6$ and $38$, in that order. Assuming the disk head is currently at cylinder $20$, what is the time taken to satisfy all the ... cylinder to adjacent one and Shortest Seek Time First (SSTF) algorithm is used? $240$ milliseconds $96$ milliseconds $120$ milliseconds $112$ milliseconds
16
Consider a hypothetical machine with $3$ pages of physical memory, $5$ pages of virtual memory, and $<A, B, C, D, A, B, E, A, B, C, D, E, B, A, B>$ as the stream of page reference by an application. If $P$ and $Q$ are the number of page faults that the application ... respectively, then $(P,Q)=$ _______(Assuming enough space for storing $3$ page frames) $(11,10)$ $(12,11)$ $(10,11)$ $(11,12)$
17
Consider the following statements about user level threads and kernel level threads. Which one of the following statements is FALSE? Context switch time is longer for kernel level threads than for user level threads. User level threads do not need any ... threads can be scheduled on different processors in a multi-processor system. Blocking one kernel level thread blocks all related threads.
18
S1: Context Switching occurs only in kernel mode. :TRUE S2: Context Switching in user mode is faster as compared to context switching in kernel mode. : TRUE If Context Switching occurs only in kernel mode, then how is CS in user mode faster as compared to that ... , perform context switching and then change back to user mode which means more time should be taken as compared to CS in kernel mode.
19
Disk request come to a disk driver for cylinders in the order $10,22,20,2,40,6$ and $38,$ at a time when the disk drive is reading from cylinder $20$. The total seek time, if the disk arm scheduling algorithm is first-come-first-served is $900$ ms $850$ ms $360$ ms $876$ ms
20
Consider the following piece of C code: void main( ) { fork( ); fork( ); exit( ); } How many child processes are created upon execution of this program?
21
A computer system implements a 36 bit virtual address. Page size is 4KB and size of physical memory is 30 bits. The approximate size of page table in the system is ___ MB ? Is it 36MB or 48MB ?
22
Three processes arrive at time zero with $\text{CPU}$ bursts of $16,\;20$ and $10$ milliseconds. If the scheduler has prior knowledge about the length of the $\text{CPU}$ bursts, the minimum achievable average waiting time for these three processes in a non-preemptive scheduler (rounded to nearest integer) is _____________ milliseconds.
1 vote
23
Que. The aging algorithm with a=0.5 is used to predict run times. The previous four runs from oldest to most recent are 40, 20, 20 and 15 msec. The prediction for the next time will be: a. 15 msec b. 25 msec c. 39 msec d. 40 msec
24
Why logical address and physical address are same in case of compile and load time binding ? In complie time as i have read compiler will generate absoute address ,but this adress for the meain memory location.Logical address can be anything?Why it has ti be same as physical address?
25
Consider a computer system with multiple shared resource types, with one instance per resource type. Each instance can be owned by only one process at a time. Owning and freeing of resources are done by holding a global lock $(L)$. The ... that deadlocks will not occur The scheme may lead to live-lock The scheme may lead to starvation The scheme violates the mutual exclusion property
1 vote
26
Consider the following pseudocode, where $\textsf{S}$ is a semaphore initialized to $5$ in line $\#2$ and $\textsf{counter}$ is a shared variable initialized to $0$ in line $\#1$. Assume that the increment operation in line $\#7$ is $\textit{not}$ ... $0$ after all the threads successfully complete the execution of $\textsf{parop}$ There is a deadlock involving all the threads
1 vote
27
Consider the following multi-threaded code segment (in a mix of C and pseudo-code), invoked by two processes $P_1$ and $P_2$, and each of the processes spawns two threads $T_1$ and $T_2$: int x = 0; // global Lock L1; // global main () { create a thread to execute foo( ... will print the value of $y$ as $2.$ Both $T_1$ and $T_2$, in both the processes, will print the value of $y$ as $1.$
28
Which of the following standard $C$ library functions will always invoke a system call when executed from a single-threaded process in a $\text{UNIX/Linux}$ operating system? $\textsf{exit}$ $\textsf{malloc}$ $\textsf{sleep}$ $\textsf{strlen}$
1 vote
29
In the context of operating systems, which of the following statements is/are correct with respect to paging? Paging helps solve the issue of external fragmentation Page size has no impact on internal fragmentation Paging incurs memory overheads Multi-level paging is necessary to support pages of different sizes
1 vote
30
Which of the following statement(s) is/are correct in the context of $\text{CPU}$ scheduling? Turnaround time includes waiting time The goal is to only maximize $\text{CPU}$ utilization and minimize throughput Round-robin policy can be used even when the $\text{CPU}$ time required by each of the processes is not known apriori Implementing preemptive scheduling needs hardware support
31
Consider a three-level page table to translate a $39$-bit virtual address to a physical address as shown below: The page size is $\text{4 KB}$ = ($\text{1KB}$ $=2^{10}$ bytes) and page table entry size at every level is $8$ bytes. A process $P$ is ... $\text{2GB}$ of physical memory. The minimum amount of memory required for the page table of $P$ across all levels is _________ $\text{KB}$.
1 vote
32
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 $\textsf{foo}$. Which of ... file from $\textsf{foo}$ Renaming of an existing file in $\textsf{foo}$ Opening of an existing file in $\textsf{foo}$
33
A data file consisting of $1,50,000$ student-records is stored on a hard disk with block size of $4096$ bytes. The data file is sorted on the primary key $\textrm{RollNo}$. The size of a record pointer for this disk is $7$ bytes. Each student-record has ... disk. Assume that the records of data file and index file are not split across disk blocks. The number of blocks in the index file is ________
34
Consider a single-level page table system, with the page table stored in the memory. If the hit rate to TLB is $80\%$, and it takes $15$ nanoseconds to search the $TLB$, and $150$ nanoseconds to access the main memory, then what is the effective memory access time, in nanoseconds? $185$ $195$ $205$ $175$
35
Match $\text{List I}$ with $\text{List II}$ ... C-III, D-IVA-II, B-IV, C-III, D-IA-II, B-IV, C-I, D-IIIA-IV, B-III, C-II, D-I$Match$
36
Comprehension: For the question given below: concern a disk with a sector size of $512$ bytes, $2000$ tracks per surface, $50$ sectors per track, five double-sided platters, and average seek time of $10$ milliseconds. If $T$ is the capacity of a track in bytes, and $S$ is the capacity of each surface in ... $(T,S)=$ _______ $(50 K, 50000 K)$ $(25 K, 25000 K)$ $(25 K, 50000 K)$ $(40 K, 36000 K)$
37
Comprehension: For the question given below: concern a disk with a sector size of $512$ bytes, $2000$ tracks per surface, $50$ sectors per track, five double-sided platters, and average seek time of $10$ milliseconds. What is the capacity of the disk, in bytes? $25,000 K$ $500,000 K$ $250,000 K$ $50,000 K$
Comprehension: For the question given below: concern a disk with a sector size of $512$ bytes, $2000$ tracks per surface, $50$ sectors per track, five double-sided platters, and average seek time of $10$ milliseconds. Given below are two statements: Statement $I$: The ... $II$ are false Statement $I$ is correct but Statement $II$ is false Statement $I$ is incorrect but Statement $II$ is true
Comprehension: For the question given below, concern a disk with a sector size of $512$ bytes, $2000$ tracks per surface, $50$ sectors per track, five double-sided platters, and average seek time of $10$ milliseconds. If the disk platters rotate at $5400$ rpm ( ... minute), then approximately what is the maximum rotational delay? $0.011$ seconds $0.11$ seconds $0.0011$ seconds $1.1$ seconds
For the question given below, concern a disk with a sector size of $512$ bytes, $2000$ tracks per surface, $50$ sectors per track, five double-sided platters, and average seek time of $10$ milliseconds. If one track of data can be transferred per revolution, then what is the data transfer rate? $2,850$ KBytes/second $4,500$ KBytes/second $5,700$ KBytes/second $2,250$ KBytes/second