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Dr. NAVALAR NEDUNCHEZHIYAN COLLEGE OF ENGINEERING
II - CSE
THOLUDUR – 606 303, CUDDALORE DIST
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
ANNA UNIVERSITY CHENNAI
YEAR: II / SEM IV
CS2254 – OPERATING SYSTEMS
(Common to CSE and IT)
UNIT I PROCESSES AND THREADS
9
Introduction to operating systems – Review of computer organization – Operating system structures – System
calls – System programs – System structure – Virtual machines – Processes – Process concept – Process
scheduling – Operations on processes – Cooperating processes – Interprocess communication –
Communication in client-server systems – Case study – IPC in Linux – Threads – Multi-threading models –
Threading issues – Case study – Pthreads library.
UNIT II PROCESS SCHEDULING AND SYNCHRONIZATION
10
CPU scheduling – Scheduling criteria – Scheduling algorithms – Multiple – Processor scheduling – Real time
scheduling – Algorithm evaluation – Case study –Process scheduling in Linux – Process synchronization – The
critical-section problem– Synchronization hardware – Semaphores – Classic problems of synchronization –
Critical regions – Monitors – Deadlock system model – Deadlock characterization –Methods for handling
deadlocks – Deadlock prevention – Deadlock avoidance –
Deadlock detection – Recovery from deadlock.
UNIT III STORAGE MANAGEMENT
9
Memory management – Background – Swapping – Contiguous memory allocation –Paging – Segmentation –
Segmentation with paging – Virtual memory – Background– Demand paging – Process creation – Page
replacement – Allocation of frames –Thrashing – Case study – Memory management in Linux.
UNIT IV FILE SYSTEMS
9
File system interface – File concept – Access methods – Directory structure – File system mounting –
Protection – File system implementation – Directory implementation – Allocation methods – Free space
management – Efficiency and performance – Recovery – Log structured file systems – Case studies – File
system in Linux – File system in Windows XP.
UNIT V I/O SYSTEMS
8
I/O Systems – I/O Hardware – Application I/O interface – Kernel I/O subsystem –Streams – Performance –
Mass-storage structure – Disk scheduling – Disk management – Swap-space management – RAID – Disk
attachment – Stable storage – Tertiary storage – Case study – I/O in Linux.Total: 45
TEXT BOOK
1. Silberschatz, Galvin and Gagne, “Operating System Concepts”, 6th Edition,Wiley India Pvt. Ltd., 2003.
REFERENCES
1. Tanenbaum, A.S., “Modern Operating Systems”, 2nd Edition, Pearson Education, 2004.
2. Gary Nutt, “Operating Systems”, 3rd Edition, Pearson Education, 2004.
3. William Stallings, “Operating Systems”, 4th Edition, Prentice Hall of India, 2003.
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SUBJECT CODE:CS2254
SUBJECT NAME:OPERATING SYSTEMS
UNIT: I
PART – A
(PROCESSES AND THREADS)
(1-MARK)
1. Which directory implementation is used in most Operating System?
(A) Single level directory structure
(B) Two level directory structure
(C) Tree directory structure
(D) Acyclic directory structure
2 .The Banker’s algorithm is used
(A) to prevent deadlock in operating systems
(B) to detect deadlock in operating systems
(C) to rectify a deadlocked state
(D)none of the above
3. A thread
(A) is a lightweight process where the context switching is low
(B) is a lightweight process where the context swithching is high
(C) is used to speed up paging
(D) none of the above
4. ______ is a high level abstraction over Semaphore
(A Shared memory
(B) Message passing (C) Monitor
(D) Mutual exclusion
5. A tree sturctured file directory system
(A) allows easy storage and retrieval of file names
(B) is a much debated unecessary feature
(C) is not essential when we have millions of files
(D) none of the above
6. Shell is the exclusive feature of
(A) UNIX
(B) DOS
(C) System software
(D) Application software
7. A program in execution is called
(A) Process (B) Instruction(C) Procedure (D) Function
8. Interval between the time of submission and completion of the job is called
(A) Waiting time (B) Turnaround time(C) Throughput (D) Response time
9. A scheduler which selects processes from secondary storage device is called
(A) Short term scheduler.
(B) Long term scheduler.
(C) Medium term scheduler.
(D) Process scheduler.
10. The scheduling in which CPU is allocated to the process with least CPU-burst time is called
(A) Priority Scheduling
Robin Scheduling
(B) Shortest job first Scheduling
(C) Round
(D) Multilevel Queue Scheduling
11. The term ‘page traffic’ describes
(A) number of pages in memory at a given instant(B) number of papers required to be brought in at a
given page request(C) the movement of pages in and out of memory(D) number of pages of executing
programs loaded in memory.
12 .The “turn-around” time of a user job is the
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(A) time since its submission to the time its results become available(B) time duration for which the CPU
is allotted to the job(C) total time taken to execute the job(D) time taken for the job to move from
assembly phase to completion phase.
13 Which of the following can be used as a criterion for classification of data structures used in
language processing.
(A) nature of a data structure
(B) purpose of a data structure
(C) lifetime of a
data structure (D) all of the above.
14 Memory utilization factor shall be computed as follows
(A) memory in use/allocated memory.(B) memory in use/total memory connected.
(C) memory allocated/free existing memory.(D) memory committed/total memory available.
15.Program ‘preemption’ is
(A) forced de allocation of the CPU from a program which is executing on theCPU.
(B) release of CPU task
(C) forced allotment of CPU by a program to itself.
(D) a program terminating itself due to detection
16 .An assembler is
(A) programming language dependent.
machinedependant.
(B) syntaxdependant.
(C)
(D) datadependant.
17 Which of the following is not a fundamental process state
(A) ready(B) terminated(C) executing (D) blocked
18 ‘LRU’ page replacement policy is
(A) Last Replaced Unit. (B) Last Restored Unit.(C) Least Recently Used. (D) Least Required Unit.
19 Which of the following is true?
(A) Block cipher technique is an encryption technique.
(B) Steam cipher technique is an encryption technique.
(C) Both (A) and (B).
(D) Neither of (A) and (B).
20 Which of the following approaches do not require knowledge of the system state?
(A) deadlock detection. (B) deadlock prevention.(C) deadlock avoidance. (D) none of the above.
ANSWER:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
C
A
A
C
C
A
A
B
C
B
C
C
D
B
A
C
D
C
C
D
PART:B
(2-MARK)
21. What is an Operating system?.(A.U/NOV/DEC 2008)
An operating system is a program that manages the computer hardware. It also provides a basis for
application programs and act as an intermediary between a user of a computer and the computer hardware.
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It controls and coordinates the use of the hardware among the various application programs for the various
users.
22. Why is the Operating System viewed as a resource allocate& control program?
A computer system has many resources - hardware & software that may be required to solve a problem,
like CPU time, memory space, file-storage space, I/O devices & so on. The OS acts as a manager for these
resources so it is viewed as a resource allocator.The OS is viewed as a control program because it
manages the execution of user programs to prevent errors & improper use of the computer.
23. What is the Kernel?
A more common definition is that the OS is the one program running at all times on the computer, usually
called the kernel, with all else being application programs.
24. What are Batch systems?
Batch systems are quite appropriate for executing large jobs that need little interaction. The user can
submit jobs and return later for the results. It is not necessary to wait while the job is processed. Operators
batched together jobs with similar needs and ran them through the computer as a group.
25. What is the advantage of Multiprogramming?.(A.U/NOV/DEC 2012)
Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to
execute. Several jobs are placed in the main memory and the processor is switched from job to job as
needed to keep several jobs advancing while keeping the peripheral devices in use. Multiprogramming is
the first instance where the Operating system must make decisions for the users. Therefore they are fairly
sophisticated.
26. What is an Interactive computer system? (A.U/NOV/DEC 2011)
Interactive computer system provides direct communication between the user and the system. The user
gives instructions to the operating system or to a program directly, using a keyboard or mouse, and waits
for immediate results.
27. What do you mean by Time-sharing systems?(A.U/APRIL/MAY 2009)
Time-sharing or multitasking is a logical extension of multiprogramming. It allows many users to share
the computer simultaneously. The CPU executes multiple jobs by switching among them, but the switches
occur so frequently that the users can interact with each program while it is running.
28. What are multiprocessor systems & give their advantages?(A.U/APRIL/MAY 2011)
Multiprocessor systems also known as parallel systems or tightly coupled systems are systems that have
more than one processor in close communication, sharing the computer bus, the clock and sometimes
memory & peripheral devices. Their main advantages are
• Increased throughput
• Economy of scale
• Increased reliability
29. What are the different types of multiprocessing?.(A.U/NOV/DEC 2009)
Symmetric multiprocessing (SMP): In SMP each processor runs an identical copy of the Os& these
copies communicate with one another as needed. All processors are peers. Examples are Windows
NT, Solaris, Digital UNIX, and OS/2 & Linux.
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Asymmetric multiprocessing: Each processor is assigned a specific task. A master processor controls the
system; the other processors look to the master for instructions or predefined tasks. It defines a masterslave relationship. Example SunOS Version 4.
30. What is graceful degradation?(A.U/APRIL/MAY 2012)
In multiprocessor systems, failure of one processor will not halt the system, but only slow it down. If there
are ten processors & if one fails the remaining nine processors pick up the work of the failed processor.
This ability to continue providing service is proportional to the surviving hardware is called graceful
degradation.
31. What is Dual-Mode Operation?
The dual mode operation provides us with the means for protecting operating system from wrong users
and wrong users from one another. User mode and monitor mode are the two modes. Monitor mode is also
called supervisor mode, system mode or privileged mode. Mode bit is attached to the hardware of the
computer to indicate the current mode. Mode bit is '0' for monitor mode and '1' for user mode.
32. What are privileged instructions?
Some of the machine instructions that may cause harm to a system are designated as privileged
instructions. The hardware allows the privileged instructions to be executed only in monitor mode.
33. How can a user program disrupt the normal operations of a system?
A user program may disrupt the normal operation of a system by
• Issuing illegal I/O operations
• by accessing memory locations within the OS itself
• Refusing to relinquish the CPU
34. How is the protection for memory provided?.(A.U/NOV/DEC 2008)
The protection against illegal memory access is done by using two registers. The base register and the
limit register. The base register holds the smallest legal physical address; the limit register contains the
size of the range. The base and limit registers can be loaded only by the OS using special privileged
instructions.
35. What are the various OS components?(A.U/APRIL/MAY 2008)
The various system components are
• Process management
• Main-memory management
• File management
• I/O-system management
• Secondary-storage management
• Networking
• Protection system
• Command-interpreter system
36.What is a process?(A.U/APRIL/MAY 2008)
A process is a program in execution. It is the unit of work in a modern operating system. A process is an
active entity with a program counter specifying the next instructions to execute and a set of associated
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resources. It also includes the process stack, containing temporary data and a data section containing
global variables.
37. What is a process state and mention the various states of a process?
As a process executes, it changes state. The state of a process is defined in part by the current activity of
that process. Each process may be in one of the following states:
• New
• Running
• Waiting
• Ready
• Terminated
38. What is process control block?.(A.U/NOV/DEC 2008)(A.U/APRIL/MAY 2013)
Each process is represented in the operating system by a process control block also called a task control
block. It contains many pieces of information associated with a specific process. It simply acts as a
repository for any information that may vary from process to process. It contains the following
information:
• Process state
• Program counter
• CPU registers
• CPU-scheduling information
• Memory-management information
• Accounting information
• I/O status information
39. What are the use of job queues, ready queues & device queues?(A.U/APRIL/MAY 2009)
As a process enters a system, they are put into a job queue. This queue consists of all jobs in the system.
The processes that are residing in main memory and are ready & waiting to execute are kept on a list
called ready queue. The list of processes waiting for a particular I/O device is kept in the device queue.
40. What is meant by context switch?(A.U/NOV/DEC 2011)
Switching the CPU to another process requires saving the state of the old process and loading the saved
state for the new process. This task is known as context switch.
PART:C
(16 MARKS)
41. Explain the various types of computer systems.(A.U/APRIL/MAY 2012)
42. Explain how protection is provided for the hardware resources by the operating system.
43. What are the system components of an operating system and explain them?
44. What are the various process scheduling concepts?(A.U/NOV/DEC 2011)(A.U APRIL/MAY 13)
45. Explain about inter process communication.(A.U/NOV/DEC 2008)
46. List five services provided by an operating system. Explain how each provides convenience to
the users. Explain also in which cases it would be impossible for user level programs to provide
these services.
47. How does multi programming help in achieving improved utilization of a computer system?
(A.U/APRIL/MAY 2008)
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48. With necessary diagram explain the term "process" from the operating system point of
view.(A.U/APRIL/MAY 2008)(A.U/NOV/DEC 2011)(A.U/APRIL/MAY 2013)
49.Explaininterprocess communication(A.U/APRIL/MAY 2009)(A.U/APRIL/MAY 2012)
50. What are the various process scheduling concepts?(A.U//NOV/DEC 2010)
UNIT-II(PROCESS SCHEDULING AND SYNCHRONIZATION)
PART: A
(1-MARK)
51 Program generation activity aims at
(A) Automatic generation of program(B) Organize execution of a program written in PL
(C) Skips generation of program
(D) Speedens generation of program
52 Which amongst the following is not an advantage of Distributed systems?
(A) Reliability (B) Incremental growth(C) Resource sharing (D) None of the above
53 An imperative statement
(A) Reserves areas of memory and associates names with them
(B) Indicates an action to be performed during execution of assembled program
(C) Indicates an action to be performed during optimization
(D) None of the above
54 Which of the following loader is executed when a system is first turned on or restarted
(A) Boot loader (B) Compile and Go loader(C) Bootstrap loader (D) Relating loader
55 Poor response time is usually caused by
(A) Process busy(B) High I/O rates(C) High paging rates(D) Any of the above
56 “Throughput” of a system is
(A) Number of programs processed by it per unit time
(B) Number of times the program is invoked by the system
(C) Number of requests made to a program by the system (D) None of the above
57 The “blocking factor” of a file is
(A) The number of blocks accessible to a file
(B) The number of blocks allocated to a file
(C) The number of logical records in one physical record
(D) None of the above
58 Which of these is a component of a process precedence sequence?
(A) Process name (B) Sequence operator ‘;’(C) Concurrency operator ‘,’ (D) All of the above
59 Which amongst the following is valid syntax of the Fork and Join Primitive?
(A) Fork <label> (B) Fork <label>Join <var>Join <label>
(C) For <var> (D) Fork <var>Join <var>join<var>
60 Nested Macro calls are expanded using the
(A) FIFO rule (First in first out)
(First in last out)
(B) LIFO (Last in First out)
(C) FILO rule
(D) None of the above
61 A parser which is a variant of top-down parsing without backtracking is
(A) Recursive Descend. (B) Operator Precedence.(C) LL(1) parser. (D) LALR Parser.
62 The expansion of nested macro calls follows
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(A) FIFO rule.
(B) LIFO rule (C) LILO rule.
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(D) priority rule.
63. In a two-pass assembler, the task of the Pass II is to
(A) separate the symbol, mnemonic opcode and operand fields.(B) build the symbol table.
(C) construct intermediate code.
(D) synthesize the target program.
64 A linker program
(A) places the program in the memory for the purpose of execution.
(B) relocates the program to execute from the specific memory are allocated to it.
(C) links the program with other programs needed for its execution.
(D) interfaces the program with the entities generating its input data.
65 Which scheduling policy is most suitable for a time-shared operating system
(A) Shortest-job First. (B) Elevator.(C) Round-Robin. (D) First-Come-First-Serve.
66 A critical section is a program segment
(A) which should run in a certain specified amount of time.
(B) which avoids deadlocks.(C) where shared resources are accessed.
(D) which must be enclosed by a pair of semaphore operations, P and V.
67 An operating system contains 3 user processes each requiring 2 units of resource R The
minimum number of units of R such that no deadlocks will ever arise is
(A) 4. (B) 3.(C) 5. (D) 6.
68 Locality of reference implies that the page reference being made by a process
(A) will always be to the page used in the previous page reference.
(B) is likely to be the one of the pages used in the last few page references.
(C) will always be to one of the pages existing in memory.
(D)will always lead to a page fault.
69 Which of these is not a part of Synthesis phase
(A) Obtain machine code corresponding to the mnemonic from theMnemonics table
(B) Obtain address of a memory operand from the symbol table
(C) Perform LC processing
(D) Synthesize a machine instruction or the machine form of a constant
70 The syntax of the assembler directive EQU is
(A) EQU <address space>
(B) <symbol>EQU<address space>
(C) <symbol>EQU
(D) None of the above
ANSWERS:
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
A
A
B
C
D
A
C
D
A
B
A
B
D
C
C
C
A
B
C
B
PART: B
(2 MARK)
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71. What is a thread?(A.U/APRIL/MAY 2009)(A.U/NOV/DEC 2011)
II - CSE
A thread otherwise called a lightweight process (LWP) is a basic unit of CPU utilization, it comprises of a
thread id, a program counter, a register set and a stack. It shares with other threads belonging to the same
process its code section, data section, and operating system resources such as open files and signals.
72. What are the benefits of multithreaded programming?(A.U/APRIL/MAY 2008)
The benefits of multithreaded programming can be broken
down into four major categories:
• Responsiveness
• Resource sharing
• Economy
• Utilization of multiprocessor architectures
73.Compare user threads and kernel threads.(A.U/APRIL/MAY 2010)
User threads User threads are supported above the kernel and are implemented by a thread library at the
user level. Thread creation & scheduling are done in the user space, without kernel intervention. Therefore
they are fast to create and manage blocking system call will cause the entire process to block Kernel
threads
Kernel threads are supported directly by the operating system .
74. What is the use of fork and exec system calls?
Fork is a system call by which a new process is created. Exec is also a system call, which is used after a
fork by one of the two processes to replace the process memory space with a new program.
75. Define thread cancellation & target thread.(A.U/APRIL/MAY 2012)(A.U/APRIL/MAY 2013)
The thread cancellation is the task of terminating a thread before it has completed. A thread that is to be
cancelled is often referred to as the target thread. For example, if multiple threads are concurrently
searching through a database and one thread returns the result, the remaining threads might be cancelled.
76. What are the different ways in which a thread can be cancelled?
Cancellation of a target thread may occur in two different scenarios:
• Asynchronous cancellation: One thread immediately terminates the target thread is called asynchronous
cancellation.
• Deferred cancellation: The target thread can periodically check if it should terminate, allowing the target
thread an opportunity to terminate itself in an orderly fashion.
77. Define CPU scheduling.(A.U/APRIL/MAY 2009)
CPU scheduling is the process of switching the CPU among various processes. CPU scheduling is the
basis of multiprogrammed operating systems. By switching the CPU among processes, the operating
system can make the computer more productive.
78. What is preemptive and non preemptive scheduling?(A.U/APRIL/MAY 2010)
Under non preemptive scheduling once the CPU has been allocated to a process, the process keeps the
CPU until it releases the CPU either by terminating or switching to the waiting state. Preemptive
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scheduling can preempt a process which is utilizing the CPU in between its execution and give the CPU to
another process.
79. What is a Dispatcher?(A.U/NOV/DEC 2008)(A.U/NOV/DEC 2011)
The dispatcher is the module that gives control of the CPU to the process selected by the short-term
scheduler. This function involves:
• Switching context
• Switching to user mode
• Jumping to the proper location in the user program to restart that program.
80. What is dispatch latency?
The time taken by the dispatcher to stop one process and start another running is known as dispatch
latency.
81. What are the various scheduling criteria for CPU scheduling?(A.U/APRIL/MAY 2012)
The various scheduling criteria are • CPU utilization • Throughput
• Turnaround time • Waiting time • Response time
82. Define throughput?
Throughput in CPU scheduling is the number of processes that are completed per unit time. For long
processes, this rate May be one process per hour; for short transactions, throughput Might be 10 processes
per second.
83. What is turnaround time?(A.U/APRIL/MAY 2010)
Turnaround time is the interval from the time of submission to the time of completion of a process. It is
the sum of the periods spent waiting to get into memory, waiting in the ready queue, executing on the
CPU, and doing I/O.
84. Define race condition.
When several process access and manipulate same data concurrently, then the outcome of the execution
depends on particular order in which the access takes place is called race condition. To avoid race
condition, only one process at a time can manipulate the shared variable.
85. What is critical section problem?(A.U/APRIL/MAY 2010)
Consider a system consists of 'n' processes. Each process has segment of code called a critical section, in
which the process may be changing common variables, updating a table, writing a file. When one process
is executing in its critical section, no other process can allowed executing in its critical section.
86. What are the requirements that a solution to the critical section problem must satisfy?
The three requirementsare
(i) Mutual exclusion(ii) Progress (iii) Bounded waiting
87. Define entry section and exit section.
The critical section problem is to design a protocol that the processes can use to cooperate. Each process
must request permission to enter its critical section. The section of the code implementing this request is
the entry section. The critical section is followed by an exit section. The remaining code is the remainder
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section
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88.Give two hardware instructions and their definitions which can be
Used for implementing mutual exclusion.
• Test And Set
Boolean TestAndSet (Boolean &target)
{Boolean rv = target;
Target = true; return rv;
}• Swap Void Swap (Boolean &a, Boolean &b)
{Boolean temp = a;
a = b;
b = temp;
}
89. What is a semaphore?(A.U/APRIL/MAY 2009)(A.U/APRIL/MAY 2013)
A semaphore 'S' is a synchronization tool which is an integer value that, apart from initialization, is
accessed only through two standard atomic operations; wait and signal.
wait (S)
{while (S<=0); S--;} The classic definition of 'signal'
signal (S)
{S++;}
90. Define busy waiting and spin lock.(A.U/APRIL/MAY 2010)
When a process is in its critical section, any other process that tries to enter its critical section must loop
continuously in the entry code. This is called as busy waiting and this type of semaphore is also called a
spin lock, because the process while waiting for the lock.
PART: C
(16-MARK)
91. Give an overview about threads.
92. Explain in detail about the threading issues.
93. Write about the various CPU scheduling algorithms.(A.U/NOV/DEC 2011)
94. What is critical section problem and explain two process solutions and multiple process
solutions?(A.U/APRIL/MAY 2009)
95. Explain what semaphores are, their usage, implementation given to avoid busy waiting and
binary semaphores.(A.U/APRIL/MAY 2008)
96. Explain about critical regions and monitors
97. Consider the following set of processes, with the length of CPU-burst time given in millisecond.
Process Burst time Priority (A.U.APRIL/MAY 2008)(A.U/NOV/DEC 2011)
p1 10 3 p2 1 1 p3 2 3 p4 1 4 p5 5 2
the processes are assumed to have arrived in order p1, p2, p3, p4, p5 all at time 0. (i) Draw Gantt
chats illustrating the execution of these processes using FCFS, SJF, a non-preemptive priority ( a
smaller priority number implies a higher priority) and RR (quantum=1) scheduling (ii) What is the
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turn around time of each process for each of the scheduling algorithms(A.U/APRIL/MAY
2012)(A.U/APRIL/MAY 2013)
98. Explain what semaphores are, their usage, implementation given to avoid busy waiting and
binary semaphores(A.U/APR/MAY 2009)(A.U/APRIL/MAY 2008)
99.Write about the various CPU scheduling algorithms(A.U/APR/MAY 2010)(A.U/APRIL/MAY
2012)(A.U/APRIL/MAY 2013)
UNIT: III(STORAGE MANAGEMENT)
PART:A
(1 MARK)
100.The following features are needed to implement top down parsing
(A) Source string marker
(B) Prediction making mechanism
(C) Matching and Backtracking mechanism (D) All of the above
101.A macro definition consists of
(A) A macro prototype statement
(B) One or more model statements
(C) Macro pre-processor statements
(D) All of the above
102The main reason to encrypt a file is to ______________.
(A) Reduce its size
(B) Secure it for transmission
(C) Prepare it for backup
(D) Include it in the start-up sequence
103.Which of the following is not a key piece of information, stored in single page table entry,
assuming pure paging and virtual memory
(A) Frame number
(B) A bit indicating whether the page is in physical memory or on the disk
(C) A reference for the disk block that stores the page
(D) None of the above
104.A UNIX device driver is
(A) Structured into two halves called top half and bottom half
(B)Three equal partitions
(C)Unstructured
(D)None of the above
105.The following is not a layer of IO management module
(A) PIOCS (Physical Input Output Control System)(B) LIOCS (Logical Input Output Control System)
(C) FS (File System)
(D) MCS (Management Control System)
106.Which amongst the following is not a valid page replacement policy?
(A) LRU policy (Least Recently Used) (B) FIFO policy (First in first out)
(C) RU policy (Recurrently used)
(D) Optimal page replacement policy
107Consider a program with a linked origin of 5000. Let the memory area allocated to it have the
start address of 70000. Which amongst the following will be the value to be loaded in relocation
register?
(A) 20000
(B) 50000
(C) 70000
(D) 90000
108.An assembly language is a
(A) low level programming language
(B) Middle level programming language
(C) High level programming language
(D) Internet based programming language
109.TII stands for
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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(A) Table of incomplete instructions
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(B) table of information instructions
(C) translation of instructions information
(D) translation of information instruction
Q.110.An analysis, which determines the syntactic structure of the source statement, is called
(A) Sementic analysis
(B) process analysis
(C) Syntax analysis
(D) function analysis
111.Action implementing instruction’s meaning are a actually carried out by
(A) Instruction fetch (B) Instruction decode(C) instruction execution
(D) Instruction program
112.The field that contains a segment index or an internal index is called
(A) target datum
(B) target offset
(C) segment field
(D) fix dat
113.A program in execution is called
(A) process
(B) function
(C) CPU
(D) Memory
114.Jobs which are admitted to the system for processing is called
(A) long-term scheduling
(B) short-term scheduling
(C) medium-term scheduling (D) queuing
115.A set of techniques that allow to execute a program which is not entirely in memory is called
(A) demand paging
(B) virtual memory
(C) auxiliary memory
(D) secondary memory
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
A
A
B
C
D
A
C
D
A
B
A
B
D
C
C
C
A
B
C
B
116. SSTF stands for
(A) Shortest-Seek-time-first scheduling
(B) small – small-time-first
(C) simple-seek-time-first
(D) small-simple-time-first scheduling
117.Before proceeding with its execution, each process must acquire all the resources it needs is
called
(A) hold and wait
(B) No pre-emption
(C) circular wait
(D) starvation
118.Virtual memory is
(A) simple to implement
(B) used in all major commercial operating systems
(C) less efficient in utilization of memory
(D) useful when fast I/O devices are not available
119.Relocation bits used by relocating loader are specified by
(A) Relocating loader itself (B) Assembler or Translator(C) Macro processor
(D) Both (A) and (B)
ANSWER
PART: B
(2 MARK)
120. Define deadlock.(A.U/APRIL/MAY 2009)
A process requests resources; if the resources are not available at that time, the process enters a wait state.
Waiting processes may never again change state, because the resources they have requested are held by
other waiting processes. This situation is called a deadlock.
121. What is the sequence in which resources may be utilized?(A.U/NOV/DEC 2008)
Under normal mode of operation, a process may utilize a resource in the following sequence:
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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• Request: If the request cannot be granted immediately, then the requesting process must wait until it can
acquire the resource.
• Use: The process can operate on the resource.
• Release: The process releases the resource.
122. What are conditions under which a deadlock situation may arise?(A.U/APRIL/MAY
2008)(A.U/APRIL/MAY 2013)
A deadlock situation can arise if the following four conditions hold simultaneously in a system: (a) Mutual
exclusion
b. Hold and wait
c. No pre-emption
123. What is a resource-allocation graph?(A.U/APRIL/MAY 2009)(A.U/APRIL/MAY 2012)
Deadlocks can be described more precisely in terms of a directed graph called a system resource
allocation graph. This graph consists of a set of vertices V and a set of edges E. The set of vertices V is
partitioned into two different types of nodes; P the set consisting of all active processes in the system and
R the set consisting of all resource types in the system.
124. Define request edge and assignment edge.
A directed edge from process Pi to resource type Rj is denoted by PiàRj; it signifies that process Pi
requested an instance of resource type Rj and is currently waiting for that resource. 125. What are the
methods forhandling deadlocks?(A.U.APRIL/MAY2010)
The deadlock problem can be dealt with in one of the three ways:
a. Use a protocol to prevent or avoid deadlocks, ensuring that the system will never enter a deadlock state.
b. Allow the system to enter the deadlock state, detect it and then recover.
c. Ignore the problem all together, and pretend that deadlocks never occur in the system.
126. Define deadlock prevention.(A.U/NOV/DEC 2011)(A.U/APRIL/MAY 2008)
Deadlock prevention is a set of methods for ensuring that at least one of the four necessary conditions like
mutual exclusion, hold and wait, no preemption and circular wait cannot hold. By ensuring that that at
least one of these conditions cannot hold, the occurrence of a deadlock can be prevented.
127. Define deadlock avoidance.
An alternative method for avoiding deadlocks is to require additional information about how resources are
to be requested.
128.What area safe state a allocation stateif, for each Pi, the resource that Pi can still request can be
satisfied by the current available resource plus the resource held by all the Pj, with j<i. if no such sequence
exists, then the system state is said to be unsafe.
129. What is banker's algorithm?(A.U/APRIL/MAY 2010)(A.U/APRIL/MAY 2012/13)
Banker's algorithm is a deadlock avoidance algorithm that is applicable to a resource- allocation system
with multiple instances of each resource type. The two algorithms used for its implementation are:
a. Safety algorithm: The algorithm for finding out whether or not a system is in a safe state.
b. Resource-request algorithm: if the resulting resource allocation is safe, the transaction is
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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completedand process Pi is allocated its resources. If the new state is unsafe Pi must
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wait and the old resource-allocation state is restored.
130. Define logical address and physical address.
An address generated by the CPU is referred as logical address. An address seen by the memory unit that
is the one loaded into the memory address register of the memory is commonly referred to as physical
address.
131. What is logical address space and physical address space?
The set of all logical addresses generated by a program is called a logical address space; the set of all
physical addresses corresponding to these logical addresses is a physical address space.
132. What is the main function of the memory-management unit?(A.U.APRIL/MAY2010)
The runtime mapping from virtual to physical addresses is done by a hardware device called a memory
management unit (MMU).
133.Define dynamic loading.
To obtain better memory-space utilization dynamic loading is used. With dynamic loading, a routine is not
loaded until it is called. All routines are kept on disk in a replaceable load format. The main program is
loaded into memory and executed. If the routine needs another routine, the calling routine checks whether
the routine has been loaded. If not, the replaceable linking loader is called to load the desired program into
memory.
134. Define dynamic linking.
Dynamic linking is similar to dynamic loading, rather that loading being postponed until execution time,
linking is postponed. This feature is usually used with system libraries, such as language subroutine
libraries. A stub is included in the image for each library- routine reference. The stub is a small piece of
code that indicates how to locate the appropriate memory-resident library routine, or how to load the
library if the routine is not already present.
135.What are overlays And an unsafe state?(A.U.APRIL/MAY2008)
A state is safe if the system can allocate resources to each process in some order and still avoid a
deadlock. A system is in safe state only if there exists a safe sequence. A sequence of processes <P1, P2,
Pn> is a safe sequence for the current to enable a process to be larger than the amount of memory
allocated to it, overlays are used. The idea of overlays is to keep in memory only those instructions and
data that are needed at a given time. When other instructions are needed, they are loaded into space
occupied previously by instructions that are no longer needed.
136. Define swapping.(A.U/NOV/DEC 2010)
A process needs to be in memory to be executed. However a process can be swapped temporarily out of
memory to a backing tore and then brought back into memory for continued execution. This process is
called swapping.
137. What are the common strategies to select a free hole from a set of available holes?
The most common strategies are
a. First fit
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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b. Best fit
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c. Worst fit
138. What do you mean by best fit?(A.U/NOV/DEC 2011)
Best fit allocates the smallest hole that is big enough. His entire list has to be searched, unless it is sorted
by size. His strategy produces the smallest leftover hole.
139. What do you mean by first fit?(A.U/APRIL/MAY 2012)
First fit allocates the first hole that is big enough. Searching can either start at the beginning of the set of
holes or where the previous first-fit search ended. Searching can be stopped as soon as a free hole that is
big enough is found.
PART:C
(16 MARK)
140. Give a detailed description about deadlocks and its characterization(A.U/APRIL/MAY
2012)(A.U/APRIL/MAY 2013)
141. Explain about the methods used to prevent deadlocks(A.U/NOV/DEC 2011)
142. Explain the Banker’s algorithm for deadlock avoidance.(A.U/APRIL/MAY 2012)
143. Explain about contiguous memory allocation.(A.U/APRIL/MAY 2013)
144.Give the basic concepts about paging.
145.Explain about the techniques for structuring the page table.
146.Explain the basic concepts of segmentation
147.. Explain the concept of demand paging. (A.U.APRIL/MAY2008)
148. How does the system detect trashing? Once it detects trashing what the system do to eliminate
this problem?
149. Explain some of the most common techniques for structuring the page table.
150. Explain the principles of segmentation with examples. (A.U.APRIL/MAY2008)
151.Give the basic concepts about paging.(A.U/APR/MAY 2009)
152.Explain the basic concepts of segmentation (A.U/NOV/DEC 2009)(A.U/NOV/DEC 2011)
153.Explain about the methods used to prevent deadlocks(A.U/APR/MAY 2010)
154. Explain the Banker’s algorithm for deadlock avoidance.(A.U/NOV/MAY 2010)
UNIT:IV(FILE SYSTEMS)
PART: A
(1 MARK)
155Resolution of externally defined symbols is performed by
(A) Linker
(B) Loader
(C) Compiler (D) Editor
156Relocatable programs
(A) cannot be used with fixed partitions
need a linker
(B) can be loaded almost anywhere in memory(C) do not
(D) can be loaded only at one specific location
157Page stealing
(A) is a sign of efficient system
(B) is taking page frames other working sets
(C) should be the tuning goal
(D) is taking larger disk spaces for pages paged out
158The total time to prepare a disk drive mechanism for a block of data to be read
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from is its
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(A) latency
(B) latency plus transmission time
(C) latency plus seek time
(D) latency plus seek time plus transmission time
159To avoid race condition, the maximum number of processes that may be simultaneously inside
the critical section is
(A) zero
(B) one
(C) two
(D) more than two
160The memory allocation scheme subject to “external” fragmentation is
(A) segmentation(B) swapping(C) pure demand paging (D) multiple fixed contiguous partitions
161Page fault frequency in an operating system is reduced when the
(A) processes tend to the I/O-bound
(B) size of pages is reduced
(C) processes tend to be CPU-bound
(D) locality of reference is applicable to the process
162.In which of the following page replacement policies Balady’s anomaly occurs?
(A) FIFO
(B) LRU
(C) LFU
(D) NRU
163.Which of the following are language processors?
(A) Assembler
(B) Compiler
(C) Interpreter
(D) All of the above
164.Virtual memory can be implemented with
(A) Segmentation
(B) Paging
(C) None
(D) all of the above
165.Recognition of basic syntactic constructs through reductions, this task is performedby
(A) Lexical analysis (B) Syntax analysis
(C) Semantic analysis
(D) Structure analysis
166.A grammar for a programming language is a formal description of
(A) Syntax
(B) Semantics (C) Structure
(D) Code
167___________ is a technique of temporarily removing inactive programs from the memory of
computer system
(A) Swapping (B) Spooling
(C) Semaphore
(D) Scheduler
168.___________ is a technique of improving the priority of process waiting in Queue for CPU
allocation
(A) Starvation (B) Ageing
(C) Revocation
(D) Relocation
169.________ is the time required by a sector to reach below read/write head.
(A) Seek Time
(B) Latency Time
(C) Access time
(D) None
170Which of the following is most general phase structured grammar?
(A) Context – Sensitive
(B) Regular
(C) Context – Free
(D) None of the above
171File record length
(A) Should always be fixed
(B) Should always be variable
(C) Depends upon the size of file
(D) Should be chosen to match the data characteristics.
172. Round robin scheduling is essentially the preemptive version of ________.
(A) FIFO (B) Shortest job first (C)Shortes remaining (D) Longest time first
173.A page fault occurs
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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(A)when the page is not in the memory
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(B) when the page is in the memory
(C) when the process enters the blocked state
(D)when the process is in the ready state
174 Which of the following will determine your choice of systems software for your computer ?
(A)Is the applications software you want to use compatible with it (B)Is it expensive
(C)Is it compatible with your hardware (D)Both 1 and 3
ANSWERS:
155
A
156
B
157
B
158
C
159
B
160
A
161
D
162
A
163
D
164
D
16
16
16
16
16
17
17
17
17
17
5
6
7
8
9
0
1
2
3
4
B
C
A
B
B
A
D
A
A
D
PART:B
(2 MARK)
175. What is virtual memory?(A.U/APRIL/MAY 2008)
Virtual memory is a technique that allows the execution of processes that may not be completely in
memory. It is the separation of user logical memory from physical memory. This separation provides an
extremely large virtual memory, when only a smaller physical memory is available.
176. What is Demand paging?(A.U/APRIL/MAY 2009)(A.U/NOV/DEC 2011)
Virtual memory is commonly implemented by demand paging. In demand paging, the pager brings only
those necessary pages into memory instead of swapping in a whole process. Thus it avoids reading into
memory pages that will not be used anyway, decreasing the swap time and the amount of physical
memory needed.
177. Define lazy swapper.
Rather than swapping the entire process into main memory, a lazy swapper is used. A lazy swapper never
swaps a page into memory unless that page will be needed.
178. What is a pure demand paging?(A.U.APRIL/MAY2010)
When starting execution of a process with no pages in memory, the operating system sets the instruction
pointer to the first instruction of the process, which is on a non-memory resident page, the process
immediately faults for the page. After this page is brought into memory, the process continues to execute,
faulting as necessary until every page that it needs is in memory. At that point, it can execute with no
more faults. This schema is pure demand paging.
179. Define effective access time.(A.U/APRIL/MAY 2012)
Let p be the probability of a page fault (0£p£1). The value of p is expected to be close to 0; that is, there
will be only a few page faults. The effective access time is Effective access time = (1-p) * ma + p * page
fault time. a : memory-access time
180. Define secondary memory.
This memory holds those pages that are not present in main memory. The secondary memory is usually a
high speed disk. It is known as the swap device, and the section of the disk used for this purpose is known
as swap space.
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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181. What is the basic approach of page replacement?(A.U/APRIL/MAY 2010)
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If no frame is free is available, find one that is not currently being used and free it. A frame can be freed
by writing its contents to swap space, and changing the page table to indicate that the page is no longer in
memory. Now the freed frame can be used to hold the page for which the process faulted.
182. What are the various page replacement algorithms used for page
replacement?(A.U/APRIL/MAY 2012)(A.U/APRIL/MAY 2013)
• FIFO page replacement
• Optimal page replacement
• LRU page replacement
• LRU approximation page replacement
• Counting based page replacement
• Page buffering algorithm.
183. What are the major problems to implement demand paging?(A.U.NOV/DEC 2008)
The two major problems to implement demand paging is developing
a. Frame allocation algorithm
b. Page replacement algorithm
184. What is a reference string?
An algorithm is evaluated by running it on a particular string of memory references and computing the
number of page faults. The string of memory reference is called a reference string.
185. What is a file?(A.U/APRIL/MAY 2008)
A file is a named collection of related information that is recorded on secondary storage. A file contains
either programs or data. A file has certain "structure" based on its type.
• File attributes: Name, identifier, type, size, location, protection, time, date
• File operations: creation, reading, writing, repositioning, deleting, truncating, appending, renaming
• File types: executable, object, library, source code etc.
186. List the various file attributes.(A.U.NOV/DEC 2008)
A file has certain other attributes, which vary from one operating system to another, but typically consist
of these: Name, identifier, type, location, size, protection, time, and date and user identification
187. What are the various file operations?(A.U/NOV/DEC 2011)
The six basic file operations are
• Creating a file
• Writing a file
• Reading a file
• Repositioning within a file
• Deleting a file
• Truncating a f
188. What is the information associated with an open file?
Several pieces of information are associated with an open
file which may be:
• File pointer
• File open count
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• Disk location of the file
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• Access rights
189. What are the different accessing methods of a file?(A.U. NOV/DEC2009)
The different types of accessing a file are:
• Sequential access: Information in the file is accessed sequentially
• Direct access: Information in the file can be accessed without any particular order.
• Other access methods: Creating index for the file, indexed sequential access method (ISAM) etc.
190. What is Directory?
The device directory or simply known as directory records information-such as name, location, size, and
type for all files on that particular partition. The directory can be viewed as a symbol table that translates
file names into their directory entries.
191. What are the operations that can be performed on a directory?(A.U.Nov/dec 2008)
The operations that can be performed on a directory are
• Search for a file
• Create a file
• Delete a file
• Rename a file
• List directory
• Traverse the file system
192. What are the most common schemes for defining the logical structure of a
directory?(A.U.APRIL/MAY2010)
The most common schemes for defining the logical structure of a directory
• Single-Level Directory
• Two-level Directory
• Tree-Structured Directories
• Acyclic-Graph Directories
• General Graph Directory
193. Define UFD and MFD.
In the two-level directory structure, each user has her own user file directory (UFD). Each UFD has a
similar structure, but lists only the files of a single user. When a job starts the system's master file
directory (MFD) is searched. The MFD is indexed by the user name or account number, and each entry
points to the UFD for that user.
194. What is a path name?
A pathname is the path from the root through all subdirectories to a specified file. In a two-level directory
structure a user name and a file name define a path name.
PART:C
(16 MARK)
195. Explain the various page replacement strategies.(A.U/APR/MAY-2008)
196. What are files and explain the access methods for files?(A.U/NOV/DEC 2011)
197. Explain the schemes for defining the logical structure of a directory.
198. Write notes about the protection strategies provided for files
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199. Consider the following page reference string:1, 2, 3, 4, 2, 1, 5, 6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3,
6.How many page faults would occur for the following replacement algorithms, assuming one, two,
three, four, five, six, or seven frames? Remember all frames are initially empty, so your first unique
pages will all cost one fault each.
• LRU replacement • FIFO replacement • Optimal replacement(A.U/APR/MAY
2009)(A.U/APRIL/MAY 2012)(A.U/APRIL/MAY 2013)
200. A page-replacement algorithm should minimize the number of page faults. We can do this
minimization by distributing heavily used pages evenly over all of memory, rather than having them
compete for a small number of page frames. We can associate with each page frame a counter of the
number of pages that are associated with that frame. Then, to replace a page, we search for the page
frame with the smallest counter. a. Define a page-replacement algorithm using this basic idea.
Specifically address the problems of (1) what the initial value of the counters is, (2) when counters
are increased, (3) when counters are decreased, and (4) how the page to be replaced is selected.
b. How many page faults occur for your algorithm for the following reference string, for four page
frames? 1, 2, 3, 4, 5, 3, 4, 1, 6, 7, 8, 7, 8, 9, 7, 8, 9, 5, 4, 5, 4, 2. c. What is the minimum number of
page faults for an optimal page replacement strategy for the reference string in part b with four
page frames?(A.U/APR/MAY-2010)(A.U/NOV/DEC 2011)
UNIT: V (I/O SYSTEMS)
PART-A
(1-MARK)
201. Let S and Q be two semaphores initialized to 1, where P0 and P1 processes the following
statements wait(S);wait(Q); ---; signal(S);signal(Q) and wait(Q); wait(S);---;signal(Q);signal(S);
respectively. The above situation depicts a _________ .
(A) Semaphore
(B)Deadlock
(C)Signal
(D)Interrupt
202.What is a shell ?
(A)It is a hardware component
(B)It is a command interpreter
(C)It is a part in compiler
(D)It is a tool in CPU scheduling
203.Routine is not loaded until it is called. All routines are kept on disk in a relocatable load format.
The main program is loaded into memory & is executed. This type of loading is called _________
(A) Static loading
(B)Dynamic loading (C) Dynamic linking
(D)Overlays
204. In the blocked state
(A)the processes waiting for I/O are found
(C)the processes waiting for the processor are found
(B)the process which is running is found
(D) none of the above
205.What is the memory from 1K - 640K called ?
(A) Extended Memory
(B)Normal Memory (C) Low Memory
(D) Conventional Memory
206.Virtual memory is __________.
(A)An extremely large main memory
(B)An extremely large secondary memory
(C)An illusion of extremely large main memory
(D)A type of memory used in super computers.
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207. The process related to process control, file management, device management, information
about system and communication that is requested by any higher level language can be performed
by __________.
(A)Editors
(B)Compilers
(C)System Call
(D)Caching
208.If the Disk head is located initially at 32, find the number of disk moves required with FCFS if
the disk queue of I/O blocks requests are 98,37,14,124,65,67.
(A) 310
(B)324
(C)315
(D)321
209.Multiprogramming systems ________.
(A)Are easier to develop than single programming systems (B)Execute each job faster
(C)Execute more jobs in the same time
(D)Are used only on large main frame computers
210.Which is not the state of the process ?
(A) Blocked
(B)Running
(C)Ready
(D) Privileged
211.The solution to Critical Section Problem is : Mutual Exclusion, Progress and Bounded Waiting.
(A) The statement is false
(B) The statement is true.
(C) The statement is contradictory.
(D)None of the above
212.The state of a process after it encounters an I/O instruction is __________.
(A) Ready
(B)Blocked/Waiting (C)Idle
(D)Running
213. The number of processes completed per unit time is known as __________.
(A)Output
(B)Throughput
(C)Efficiency
(D)Capacity
214. _________ is the situation in which a process is waiting on another process,which is also waiting
on another process ... which is waiting on the first process. None of the processes involved in this
circular wait are making progress.
(A)Deadlock (B)Starvation (C)Dormant
(D)None of the above
215. Which of the following file name extension suggests that the file is Backup copy of another file ?
(A)TXT
(B)COM
(C)BAS
(D)BAK
216Which technique was introduced because a single job could not keep both the CPU and the I/O
devices busy?
(A)Time-sharing (B)SPOOLing(C)Preemptive scheduling (D)Multiprogramming
217.The mechanism that bring a page into memory only when it is needed is called _____________
(A) Segmentation
(B)Fragmentation
(C)Demand Paging
(D)Page Replacement
218. PCB =
(A)Program Control Block
(B)Process Control Block
(C)Process Communication Block
(D)None of the above
219.FIFO scheduling is ________.
(A)Preemptive Scheduling
(C)Deadline Scheduling
(B)Non Preemptive Scheduling
(D) Fair share scheduling
220.Switching the CPU to another Process requires to save state of the old process and loading new
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
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process state is called as __________.
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(A) Process Blocking (B)Context Switch
(C)Time Sharing
(D)None of the above
ANSWERS:
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
B
B
C
A
D
C
C
D
C
D
B
B
B
B
D
D
C
B
B
B
PART:B
(2 MARK)
221. What are the various layers of a file system?(A.U.APRIL/MAY2008)
The file system is composed of many different levels. Each level in the design uses the feature of the
lower levels to create new features for use by higher levels.
• Application programs
• Logical file system
• File-organization module
• Basic file system
• I/O control
• Devices
222. What are the structures used in file-system implementation?(A.U.APRIL/MAY2000)
Several on-disk and in-memory structures are used to implement a file system a. On-disk structure include
· Boot control block
· Partition block
· Directory structure used to organize the files
File control block (FCB)
b. In-memory structure include
· In-memory partition table
· In-memory directory structure
· System-wide open file table
· Per-process open table
223. What are the functions of virtual file system (VFS)?(A.U/NOV/DEC 2011)
It has two functions
a. It separates file-system-generic operations from their implementation defining a clean VFS interface. It
allows transparent access to different types of file systems mounted locally.
b. VFS is based on a file representation structure, called anodes. It contains a numerical value for a
network-wide unique file .The kernel maintains one anode structure for each active file or directory.
224. Define seek time and latency time.(A.U.APRIL/MAY2010)
The time taken by the head to move to the appropriate cylinder or track is called seek time. Once the head
is at right track, it must wait until the desired block rotates under the read-write head. This delay is latency
time.
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
QUESTION BANK
225. What are the allocation methods of a disk space?
II - CSE
Three major methods of allocating disk space which are widely in use are
a. Contiguous allocation
b. Linked allocation
c. Indexed allocation
226.What are the advantages of Contiguous allocation?
The advantages are
a. Supports direct access
b. Supports sequential access
c. Number of disk seeks is minimal.
227. What are the drawbacks of contiguous allocation of disk space?
The disadvantages are
a. Suffers from external fragmentation
b. Suffers from internal fragmentation
c. Difficulty in finding space for a new file
d. File cannot be extended
e. Size of the file is to be declared in advance
228. What are the advantages of Linked allocation?(A.U.Nov/dec 2008)
The advantages are
a. No external fragmentation
b. Size of the file does not need to be declared
229. What are the disadvantages of linked allocation?(A.U/NOV/DEC 2011)
The disadvantages are
a. Used only for sequential access of files.
b. Direct access is not supported
c. Memory space required for the pointers.
d. Reliability is compromised if the pointers are lost or damaged
230. What are the advantages of Indexed allocation?(A.U/APRIL/MAY 2012)
The advantages are
a. No external-fragmentation problem
b. solves the size-declaration problems.
c. Supports direct access
231. How can the index blocks be implemented in the indexed allocation scheme?
The index block can be implemented as follows
a. Linked scheme
b. Multilevel scheme
c. Combined scheme
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
QUESTION BANK
232. Define rotational latency and disk bandwidth.
II - CSE
Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.
The disk bandwidth is the total number of bytes transferred, divided by the time between the first request
for service and the completion of the last transfer.
233. How free-space is managed using bit vector implementation?
The free-space list is implemented as a bit map or bit vector. Each block is represented by 1 bit. If the
block is free, the bit is 1; if the block is allocated, the bit is 0.
234. Define buffering(A.U.APRIL/MAY2009).
A buffer is a memory area that stores data while they are transferred between two devices or between a
device and an application. Buffering is done for three reasons a. To cope with a speed mismatch between
the producer and consumer of a data stream
b. To adapt between devices that have different data transfer sizes
c. To support copy semantics for application I/O
235. Define caching.(A.U.NOV/DEC/2010)
A cache is a region of fast memory that holds copies of data. Access to the cached copy is more efficient
than access to the original. Caching and buffering are distinct functions, but sometimes a region of
memory can be used for both purposes.
236. Define spooling.(A.U.APRIL/MAY2010)
A spool is a buffer that holds output for a device, such as printer, that cannot accept interleaved data
streams. When an application finishes printing, the spooling system queues the corresponding spool file
for output to the printer. The spooling system copies the queued spool files to the printer one at a time.
237. What are the various disk-scheduling algorithms?(A.U.NOV/DEC 10)(A.U/APR/MAY
2012)(A.U/APRIL/MAY 2013)
The various disk-scheduling algorithms are
a. First Come First Served Scheduling
b. Shortest Seek Time First Scheduling
c. SCAN Scheduling
d. C-SCAN Scheduling
f. LOOK scheduling
238. What is low-level formatting?
Before a disk can store data, it must be divided into sectors that the disk controller can read and write.
This process is called low-level formatting or physical formatting. Low-level formatting fills the disk with
a special data structure for each sector. The data structure for a sector consists of a header, a data area, and
a trailer.
239. What is the use of boot block?
For a computer to start running when powered up or rebooted it needs to have an initial program to run.
This bootstrap program tends to be simple. It finds the operating system on the disk loads that kernel into
memory and jumps to an initial address to begin the operating system execution. The full bootstrap
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE
QUESTION BANK
II - CSE
program is stored in a partition called the boot blocks, at fixed location on the disk. A disk that has boot
partition is called boot disk or system disk.
240. What is sector sparing?
Low-level formatting also sets aside spare sectors not visible to the operating system. The controller can
be told to replace each bad sector logically with one of the spare sectors. This scheme is known as sector
sparing or forwarding
PART:C
(16 MARK)
241. Write about the kernel I/O subsystem.
242. Explain the various disk scheduling techniques(A.U/NOV/DEC 2011)(A.U/APRIL/MAY 2013)
243. Write notes about disk management and swap-space management.
244. Suppose that a disk 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 ((in cylinders) that the disk arm moves to satisfy all
the pending requests, for each of the following disk scheduling
a. FCFS b. SSTF c. SCAN d. LOOK e. C-SCAN(A.U/NOV-DEC 2009)(A.U/APRIL/MAY
2013)(A.U/APRIL/MAY 2012)
245. Compare the performance of C-SCAN and SCAN scheduling, assuming a uniform distribution
of requests. Consider the average response time (the time between the arrival of a request and the
completion of that request’s service), the variation in response time, and the effective bandwidth.
How does performance depend on the relative sizes of seek time and rotational
latency?(A.U/NOV/DEC 2011)(A.U/APRIL/MAY 2012)
246. Describe the salient features of the file system of UNIX((A.U/APRIL/MAY 2010)
247. Explain UNIX buffer cache mechanism. (A.U/APRIL/MAY 2008)
248. Explain different disk scheduling Techniques. (A.U/APRIL/MAY 2008)
249. Explain different directory implementation methods. (A.U/APRIL/MAY 2008)
250. Write notes about disk management and swap-space management. (A.U/APRIL/MAY 2009)
(A.U/APRIL/MAY 2008)
Ms.R.SIVAGAMASUNDARI ASST.PROFESSOR/CSE