Operating System Important Questions Units Wise For External Exams
Unit 1-Intro to OS
1.What is an Operating System? Differentiate between the two views of OS? IMP2.What are the goals of an OS? IMP
3.What are the components of Operating System?
4.What are the services provided by Operating System? IMP
5.What are OS operations? Explain.
6.Give advantages of multiprocessor systems. Give features of symmetric and asymmetric
multiprocessing systems. IMP
7.Explain the below terminologies in Operating Systems
Multiprogramming systems, Multitasking systems, Multiprocessor systems. IMP
8.Describe layered approach to the design of an OS and its advantages.
9.Explain any two computing environment.
10.Explain Virtual Machine(VM) with example and diagram.What are its benefits? IMP
Unit 2-Process Mgmt
1.What is a process? With a state diagram, explain states of a process. Also writestructure of Process Control Block(PCB). IMP
2.Differentiate between long term, medium and short term schedulers.
(or explain diff type of schedulers). IMP
3.Define IPC (Interprocess Communication). Explain two models of IPC.
4.What are cooperating processes? Discuss direct and indirect communication,
5.Define the five scheduling criteria considered in Process Scheduling.
6.Explain process creation and termination.
7.Discuss three common ways of establishing relationship between user and kernel thread.
8.What is a thread? Why is it called a LWP? Discuss multithreading models. IMP
9.Discuss threading issues. IMP
10.For the processes listed below, calculate average waiting time and turnaround
time using FCF and Pre-emptive SJF
Process Arrival Time Burst Time
P1 0.0 1.5
P2 1.5 3
P3 3.0 1
P4 3.0 7.5
11. For the processes listed below, calculate average waiting time and turnaround
time using SJF(Non- pre-emptive) and SRTF(Pre-emptive)
Process Arrival Time Burst Time
P0 0 6
P1 1 3
P2 2 1
P3 3 4
12.Consider 5 processes with below arrival time, burst time and priority. Find the average waiting time and average turnaround time using
i) SRTF ii) Pre-emptive priority iii) RR (q=1)
Process Arrival Time Burst Time Priority
P1 0 7 3
P2 3 2 2
P3 4 3 1
P4 4 1 1
P5 5 3 3
Unit 3-Process Synchronization
14.Describe ‘test and set‘and ‘swap’ instructions
15.Explain the Dining Philosphers problem. IMP
16.What are monitors. Explain monitor soln to Dining Philosphers problem. IMP
17.Explain the solution for classical synchronization bounded buffer problem using semaphores. IMP
18.Explain signal and wait instructions.
Unit 4-DEADLOCKS
2)How can deadlocks be prevented? (Or explain deadlock prevention).
3)Explain various approaches for deadlock recovery. IMP
4)Define the terms: safe state and safe sequence. Give an algo to find whether or nota system is in a safe state.
5)Explain resource request algo.
6)Explain deadlock handling. Explain Bankers algo.
7)Consider the below snapshot:
Allocation Max Available
ABCD ABCD ABCD
P0 0 0 1 2 0 0 1 2 1 5 2 0
P1 1 0 0 0 1 7 5 0
P2 1 3 5 4 2 3 5 6
P3 0 6 3 2 0 6 5 2
P4 0 0 1 4 0 6 5 6
Answer the below questions using Banker’s algo:
1)What is the content of the matrix need?
2)Is the system in safe state?
3)If a request from process P1 arrives for (0,4,2,0) can the request be granted immediately? IMP
8)Consider the below snapshot:
Allocation Max Available
ABC ABC ABC
P0 0 1 2 0 1 2 5 2 0
P1 0 0 0 7 5 0
P2 3 5 4 3 5 6
P3 6 3 2 6 5 2
P4 0 1 4 6 5 6
Answer the below questions using Banker’s algo:
1)What is the content of the matrix need?
2)Is the system in safe state? If yes, write the safe sequence.
9)Consider the below snapshot:
Allocation Max Available
ABC ABC ABC
P0 0 1 0 7 5 3 3 3 2
P1 2 0 0 3 2 2
P2 3 0 2 9 0 2
P3 2 1 1 2 2 2
P4 0 0 2 4 3 3
Check whether the system is safe state or not. If yes, write the safe sequence. Further if P1 requests(1,0,2) determine if it can be granted immediately.
Unit 5-MEMORY MANAGEMENT
•Size of logical address space or memory = 2m
•Size of page =2n
•Then high order m-n bits give page no. and lower order n bits give offset.
•Number of pages= Size of logical address space or memory / Size of page
•Number of frames= Size of physical address space or memory / Size of frame
•Page size=Frame size
•Page table size = number of pages * size of each page table entry
= (Size of logical address space or memory / Size of page )* size of each page table entry
1.Given memory partitions of 270,150,600(KB)(in order) how would each of first-fit, best-fit and worst fit algorithms place the processes of 100,212 and 270(KB) in order.
2.Memory partitions of 100KB,500KB,200KB,300KB,500KB(in order) are available. How would first fit, best fit and worst fit algo place the processes of 212KB,417KB,112KB and 426KB(in order). Which algo makes efficient use of memory?
3.For a particular implementation of simple paged allocation, the page size is fixed to 4K and the total size of program is 16 Kilobytes. What is the total number of pages that are required for this program? Also calculate number of bits in the logical address.
4.For a logical address space of 8 pages of 1024 words mapped to a physical memory of 32 frames, find the number of bits in the logical address and number of bits in the physical address.- -IMP
5.Consider the system with 32-bit logical address space. Page size is 4KB and each entry in the page table is 2 Bytes long. How much memory is required for page table? What is the size of the main memory?
6.On a simple paging system with a page table containing 512 entries of 15 bits, page size of 1024 bytes, answer the following:
7.How many bits specify the offset with the page?
8.How many bits are there in the logical address?
9.What is the size of logical address space?
10.How many bits specify the page frame number?
11.How many bits are there in the physical address?
Effective Access Time for PAGING with TLB
12.Calculate the effective access-time if 20 nanoseconds is taken to access TLB,100 nanosec to access from memory and 100 nanoseconds to access frame number,
i) if hit ratio is 80% ii) if hit ratio is 98% -IMP
Soln: i) If we fail to find the page number in the associative registers (20 nanoseconds), then we must first access memory for the page table and frame number (100 nanoseconds), and then access the desired byte in memory (100 nanoseconds), for a total of 220 nanoseconds. To find the effective access time, we must weigh each case by it probability:
Effective access time = 0.80 * 120 + 0.20 * 220
= 140 nanoseconds
We suffer a 40-percent slowdown in memory access time (from 100 to 140 nanoseconds).
ii)For a 98-percent hit ratio, we have
effective access time = 0.98 * 120 + 0.02 * 220 = 122 nanoseconds
The increased hit rate produces only a 22-percent slowdown in memory access time.
13.Assume we have a paged memory system with associative registers (TLB) to hold the most active page table entries. If the page table is normally held in memory and memory access time is 1 microsec, what would be the effective access time if 85% of all memory references find their entries in the associative registers. Assume the associative registers access time is zero.
14.For a memory access system with a TLB we have TLB hit ratio of 0.9, memory access time 110 nanosecs, TLB search time 20 nanosecs. Calculate the effective memory access time.
Performance of Demand Paging
Page Fault Rate or probability of page fault 0 ? p ? 1.if p = 0 no page faults and p = 1, every reference is a fault.
Effective Access Time (EAT) = (1 – p) x memory access + p x page fault time
15.Given page-fault service time 8 msec, memory access time 100 nanosecs, page fault rate 0.0002. Calculate the effective access time (in sec).
16.On a system using demand paged memory it takes 0.12 microsec to satisfy a memory request. If the page is not in memory the request takes 5000 microsec. What would be the page fault rate needed to be to achieve an access time 1000 microsec? Assume the system is only running a single process and the CPU is idle during the page swaps.
PAGE REPLACEMENT ALGORITHM PROBLEMS
17.Consider the following reference string:
7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1
for a memory with three frames. How many page faults would occur for FIFO, OPTIMAL, ad LRU Page replacement algorithms? Which is the most efficient among them?- -IMP
Unit 6-FILE SYSTEM
Chapter -10 File System
1.Write notes on: i)File types ii)file operationsii)file attributes iv)file structure
2.Explain different file access methods.- IMP
3.Explain different directory structures.(or Explain one e.g.tree or acyclic graph structure)- IMP
Chapter -11 File System Implementation
4.Explain different disk allocation methods methods.(Explain one e.g. indexed method)- IMP
5.Explain methods of implementing directories.
6.Explain methods of free space management- IMP
Unit 7-SECONDARY STORAGE AND PROTECTION SYSTEM
Chapter -12 Secondary storage structure
1.What is disk scheduling? Explain all disk scheduling algorithms in brief.
2.Explain disk formatting.
3.Explain bad block handling.
4.Consider a disk queue with requests for I/O to blocks on below cylinders in order:
98,183,37,122,14,124,65,67. If disk head is initially at 53, calculate the head movements when the following scheduling are used i)FCFS ii)SSTF iii)SCAN iv) LOOK—IMP
5.A drive has 5000 cylinders numbered 0 to 4999. The drive is currently serving a request at cylinder 143 and the previous request was at cylinder 125. The queue of pending requests in FIFO order is: 86,1470,913,1774,948,1509,1022,1750,130. Starting from the current head position, what is the total distance travelled by the disk arm(in cylinders) to satisfy the requests using FCFS,SSTF,SCAN,LOOK. Illustrate with figure
Chapter -17 Protection
6.What are goals of protection? IMP
7.Explain access matrix model of protection.-IMP
8.Explain domain of protection.
9.Explain system and program threats. IMP
10.What are worms and viruses?
11.Distinguish between system protection and system security.
for a memory with three frames. How many page faults would occur for FIFO, OPTIMAL, ad LRU Page replacement algorithms? Which is the most efficient among them?- -IMP
18.Consider the following reference string:
R= 0 1 2 3 0 1 4 0 1 2 3 4
Calculate the number of page faults when number of frames is equal to 3 and 4 using FIFO algo. Do you notice Belady’s anamoly.
19. A process references 5 pages A,B,C,DE in the following order:
A B C D A E B C E D
Assuming that the replacement algo is “LRU” and “FIFO”, find out the number of page faults during the sequence of references, with an empty main memory with 3 frames.
20.Consider the following reference string:
1 2 3 5 2 3 5 7 2 1 2 3 8 6 4 3 2 2 3 6
for a memory with three frames. How many page faults would occur for FIFO, OPTIMAL, and LRU Page replacement algorithms?
21.Consider the following reference string:
0 9 0 1 8 1 8 7 8 7 1 2 8 2 7 8 2 3 8 3
for a memory with three frames. How many page faults would occur for FIFO, OPTIMAL, and LRU Page replacement algorithms?
22.What do you mean by a address binding? Explain with the necessary steps, the binding of instructions and data to memory addresses.
23.Describe execution time binding.
24.What is memory fragmentation? Explain internal and external fragmentation with a neat diagram. How are they overcome?¬-IMP
25.Explain the technique used to overcome external fragmentation.
26.Give differences between i) internal and external fragmentation ii) paging and segmentation.- -IMP
27.Explain i) Worst fit ii) First fit iii) Best fit storage allocation.
28.Explain the concept of paging using TLB--IMP
29.Describe TLB. How it improves memory access time with an example?
30.Explain basic concept of segmentation with respect to memory management.
31.What is Virtual Memory? Explain with examples.
32.With a diagram, discuss the steps involved in handling a page fault. -IMP
33.What is need of page replacement?
34.Describe various page replacement algorithms. Explain them with an example.
35.What do you mean by a copy-on-write? Where it is used? Explain in brief.
36.What is thrashing?- -IMP
37.What is swapping?
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