The document provides a comprehensive overview of operating systems, covering definitions, components, types, and functions. It includes explanations of process management, memory management, types of interrupts, scheduling algorithms, and inter-process communication. Additionally, it discusses concepts related to file systems, I/O systems, and synchronization mechanisms such as semaphores and critical section problems.

1. Operating systems questions and answers
Q1. What is an operating system?
An operating system is a program that manages computer hardware and provides a
basis for application programs. The primary purpose is to allow the user to easily use
the system and the secondary purpose is to use the resources in an efficient manner.
Q2. What are different views of an operating system?
There are two views of an operating system. User view defines how user sees the
operating system and involves ease of use. The system view of the operating system
involves how system resources are handled.
Q3. What are different components of the operating system?
Different components of an operating system involve – Process management,
memory management, file management, secondary storage management, IO
management and importantly inter-process scheduling.
Q4. Discuss different types of OS?
Different types of OS include single process OS, multi-process OS. Further
multiprocessing may be symmetric in which each processor is assigned a specific task
or asymmetric all processors operate and are controlled together.
Q5. What is a clustered OS?
A clustered OS handles multiple processors at the same time.
Q6. Define multi-programming, timesharing and multi-tasking.
Multiprogramming occurs when multiple processes reside in the computer memory
and cpu handles each one of them one at a time.
Timesharing is a type of multiprogramming in which each process is given a fixed unit
of CPU time.
Multitasking is same as timesharing because each process is handles one after
another by CPU.
Q7. What are the advantages of dual-mode operation?
Dual mode operating in os allows some of the instructions to be executed in
privileged mode or supervisor mode or kernel mode and is in accessible to the use. A
user mode on the other hand allows the non-privileged instructions or user defined

2. instructions to be executed and manipulated by user.
Q8. Name some of the different types of operating systems.
Real time os operate processes with predefines time constraints eg weapon systems,
flight systems.
Multimedia systems allow large amount of av data to be processed and produced at a
fast rate and need more memory and CPU speed.
Handheld systems have limited memory and display area and require smaller
programs to run.
Q9. Define the layered structure of an operating system.
Most operating systems are layered with lowest layer being hardware followed by
device controllers to control one or more devices followed by device drivers which are
programs to operate devices and then by system programs to handle io and memory
and finally shell or application programs.
Q10. What is a re-entrant program?
A program shared by multiple users each having his own data area and individual
processes.
Q11. Explain types of interrupts.
Interrupts are the signals which make the program leave the current execution of an
instruction and jump to an interrupt service routine. Interrupts may be cause due to
I/O , Timer or hardware or software error.
Q12. A computer has a 24-bit address bus and an instruction format providing 12 bits
in the address part. Calculate the max addressable memory and address offset range.
Max addressable memory is 2 to the power 24 and the offset range is 2 to the power
12.
Q13. How would relative addressing and immediate addressing be treated by
relocating loader?
An instruction using relative addressing would be unaffected by a relocating loader
since relative positions remain unchanged.
An immediate operand remains unaffected because it is supplied as explicit value
and not as an address.

3. Q14.Define operating system services.
Operating system services include user-interface, program execution, I/O operations,
File-system manipulation, communications and error-detection. The secondary
services being resource-allocation, accounting, protection and security.
Q15. What is a shell?
A shell is a command interpreter which allows a user to give commands to the os.It
interprets and passes the instructions as system calls to the kernel for further
handling.
Q16. What is an API?
Application programmer interface is the interface which provides the functions and
parameter values and return values to a programmer. Most common API’s are Win32
API, POSIX API.These API’s are treated as system calls by the kernel.
Q17.Name some system calls?
Some of the system calls are create process, terminate process, wait event, signal
event, allocate and free memory(Process control),create file, delete file, open and
close file,read,write,get and set file attributes(File management), request and release
device, get and set device attributes, read write reposition devices(Device
Management),get time or date or set time, get or set system data, get or set process
or file attributes(Information Maintainance),create or delete communication
connection, send or receive messages(Communication)
Q18. What is a system program?
A system program is the program used by os and also by system calls. Uses of
system programs are for file management, status information, file modification,
program loading and execution, programming language support and communication.
Q19. What are design goals?
Design goals of an os include the user goals and system goals to be achieved by os.
They can further be translated into policies and mechanisms.
Q20.Define structure of MS_DOS?
The layers of DOS are hardware->ROM BIOS device drivers->MS_DOS device drivers-
>system programs->application programs.
Q21. Define structure of UNIX?
The layers of Unix include (device memory and terminal controllers)->Kernel
interface->(IO, FILE, Memory management system)->system call interface->(Shell or

4. command interpreter)->user
Q22. What is a microkernel?
Microkernel is the subset of the original kernel obtained by removing all non-essential
components.
Q23. What is a virtual machine?
A virtual machine abstracts the hardware of the computer into different execution
environments giving the illusion of multiple computers.
Q24. What is a process?
A program in execution
Q25. What are process states?
Different process states are new, ready, running, waiting, terminated.
Q26. What is a PCB?
A process control block stores process info like set of registers, program counter,
process number, process states, memory limits.
Q27. What is a thread?
The basic unit of CPU processing.
Q28. What long term, short term and medium term scheduling?
Long term scheduling involves selecting processes to load from memory, short term
scheduling involves selecting process from memory to load into cpu, medium term
scheduling selects processes to be removed or loaded into memory.
Q29.What is a context switch?
The process of saving the current state of the process in the CPU and loading another
process into CPU.
Q30. What is IPC?
Inter-process communication allows processes to exchange messages among
themselves.
Q31.Differentiate between blocking and non-blocking send.

5. Blocking send occurs when a process sends a message and waits for the message to
reach the destination before send ing another message.
Q32. What is socket?
A socket is an end point in communication. A socket is created by assigning port no
and ip address to it.
It is logical extension to physical port.
Q33. What is RPC?
Remote procedure call allows a client to invoke a function on the remote server by
passing parameters and obtaining the results.
Q34. What is XDR?
External data representation involves parameter marshalling or converting machine
dependent data to machine independent form before being sent to the server.
Q35. Describe multi-threading model?
Threads are of two types kernel threads initiated by the server and user threads
initiated by the user.
Further many to one model many user level threads are mapped to a single kernel
thread.
Q36. Explain the use of thread library?
A thread library provides programmer an api for creating and managing threads.
Q37. Give examples of threads?
Pthreads are used in POSIX, Win 32 threads are used in windows and Java Threads in
Java Programming.
Q38. What is Asynchronous procedure call?
Asynchronous procedure call allows a user thread to call a particular function in
response to a particular event or signal.
Q39. Differentiate between WinXp and Linux threads?
WinXP supports fiber library supporting many to many model and has context storing

6. the thread id, register set. It distinguishes threads according to execution thread
block, kernel thread block and thread environment block.
Linux threads use fork(),exec() ans clone system calls.
Q40. Differentiate between CPU and io burst cycle.
A CPU burst cycle handles CPU bound processes while io burst cycle handles io bound
processes.
Q41. What are different scheduling algorithms?
First come first serve
Round Robin scheduling
Shortest job first
Priority scheduling (Pre-emptive and non-preemptive queue)
Shortest remaining time first
Q42. What is multi-processor scheduling?
It involves symmetric or asymmetric(individual or combined) multiprocessing and
als0o load balancing.
Q43. How is thread scheduling implemented in different operating systems?
Thread scheduling in POSIX is implemented with process contention scope for user
threads and system contention scope for kernel level threads.
Solaris divides the threads into real time, system, time-sharing and
interactive.Windows Xp assigns priority classes to threads including real time priority,
high priority, above normal priority, below normal and idle priority.
Q44. What are different types of user interfaces?
GUI, command line, API or system call, Job control language or batch processing.
Q45. Discuss system calls of UNIX?
Fork(),exec(),read90,write(),open(),close(),kill(),exit(),pause(),signal()
Q46. How does MS_DOS implement system calls?
User defined system calls can be implemented as INT 10H, INT 21H.

7. Q47, How are system calls different from library routines?
System calls are part of OS while library routines are part of object program
Q48. What would happen if running process got stuck in infinite loop in FCFS?
It would lead to infinite wait state because even if interrupts occur they would be
services thereafter the processor would take up the same process until stopped by kill
command.
Q49. Which scheduling scheme is best suited to interactive systems?
Round robin method is most preferable for interactive scheduling.
Q50. Which symbol allows a process to run in the background?
& symbol allows a process to run in background.
Q51. Why does exec command does not return any value to parent process?
Exec command is always issues by a running process which gets obliterated
thereafter.
Q 52. What is multi-level feedback queue scheduling?
In multi feedback scheduling each queue like io bound, CPU bound is assigned
processes .With time processes move from a low priority to high priority queue with
CPU bound queue given highest priority.
Q53. What is critical section problem?
Critical section problem deals with designing a protocol for different processes to co-
operate by defining entry and exit conditions for a critical section of a process. Critical
sections are those sections like updating memory, changing common variables so
that no two processes are in their critical sections at the same time to avoid errors.
Q54. What are the conditions for solution to critical section problem?
Mutual exclusion
Progress
Bounded waiting
Q55. What is Peterson’s solution to critical section problem?
Peterson’s solution involves defining flag and turn variables.
Q56. What is a semaphore?

8. Semaphore is variable shared by many processes which can be accessed by only two
atomic operations wait signal. Wait increases the value while signal decreases it.
Q57. Name different types of semaphores?
Counting
Binary
Mutex lock (locks a process)
Q58. Explain the spinlock condition.
In spinlock condition a process spins while waiting for the lock or is busy waiting.
Q59. Discuss some semaphore problems
Readers-writers problem
Producer-consumer problem
Dinning philosopher’s problem
Q60. Discuss implementation of synchronization in different operating systems.
In windows xp thread synchronization is achieved using dispatcher objects, events,
signaled state, mutex lock and thread selection.
In Linux it is implemented using pre-emption and spin-lock.
In POSIX it is implemented using Mutes lock and spinlock.
Q61. Discuss implementation of synchronization.
Databases use synchronization operations for lockind, checkpoints and atomic
transactions.
Q62. What are conditions for deadlock to occur?
Mutual exclusion
Hold and wait
No-preemption
Circular wait
Q63. Discuss some solutions to deadlock problem
Resource allocation graph

9. Banker’s algorithm
Resource-request algorithm
Safety algorithm
Q64. Differentiate between logical and physical address space.
Physical address space is how data is stores in hardware and logical address space
refers to how the user views storage in memory.
For conversion from logical to physical address space address binding is used.
Q65. What is contiguous memory allocation?
Contiguous memory allocation involves storing t5he process in different memory
holes using first fit, best fit or worst fit method.
Q66. Differentiate between external and internal fragmentation.
External fragmentation occurs because there not enough memory because allocation
and reallocation of memory.
Internal fragmentation occurs when a process is assigned a single chunk of memory
than it actually requires.
Q67. Differentiate between paging and segmentation.
Paging involves breaking up memory into equal sized pages and assigning them to a
process. The address calculation is done using page table and offset.
Segmentation method breaks up memory into unequal chunks and assigned to
various processes. The address calculation is done using segment table and offset.
Q68. How is segmentation achieved in Pentium machines?
In Pentium systems CPU generates logical addresses passed onto segmentation unit
which further passes it to paging unit and finally to physical memory.
Q69. What is virtual memory?
Virtual memory separates logical memory from physical memory by assigning a
process more logical memory than the available physical memory.
This is done by demand paging in which pages are swapped in and out of physical
memory as per process requirements.
Q70.What is pure demand paging.

10. In demand paging if a page is not found in memory a page-fault occurs and that page
is brought in memory. All the pages required by a process are loaded into memory.
In pure-demand paging we never bring a page into memory until it is required.
Q71. A computer uses an 18 bit address system with 6 bits used as page address and
12 bits as displacement. Calculate total number of pages and express the following as
paging address-
0001111000000111000
Page no (6 bits) 001111 = 15 in decimal
Displacement (12 bits) 000000111000 = 56 in decimal
Q72.In paging scheme 4 bits are reserved for page and 12 for displacement address.
How many pages can be addressed?
Since 4 bits are used for page table there will be 16 entries for pages.
Q73. In variable partition scheme compaction can be done? When it is required?
Compaction can be done when the number of free spaces reaches an optimum value.
Q74. Which memory allocation method can be used to increase cup utilization?
Optimal memory allocation.
Q75. What are possible combinations of P and M bits in virtual memory?
Since there are 2 variables total number of possible combinations is 4.
Q76. A page size is 4 Kb. How many virtual pages can be created given each page
table entry is 5 bytes and virtual address space is 4 giga bytes.
No of pages= 4GB/4KB
Q77. Why is TLB fast?
TLB is implemented as fast memory is much smaller and non-paged.
Q78. Discuss the attributes included with a file.
Name, Identifier, Type, Location, Size, Protection, Time, Date and user identification.
Q79. What operations can be performed on a file?
Create a file
Write a file

11. Read a file
Reposition in a file
Delete a file
Truncate a file
Q80.Discuss different file types.
Executable(exe,com,bin),object(obj,o),batch(bat,sh),text(txt,doc),wordprocessor(rtf,d
oc),library(lib,a,so,dll),print(ps,pdf,jpg),archive(arc,zip),multimedia(mpeg,mov,mp3,av
i)
Q81. What are different methods of accessing a file?
Sequential access
Direct access
Indexed sequential access
Q82. Name the various directory structures.
Single level directory
Two level directory
Tree structured directory
Acyclic graph directory
Graph directory structure
Q83. What are file sharing models?
Multiple users
Remote file systems
Client-server model
Distributed information system
Q84. What are file protection mechanisms?
File protection can be achieved by setting access attributes read, write, execute,
append and delete.

12. Q85. How can file systems be implemented?
Virtual file system
Partition and mounting
File control block
Q86. Discuss directory implementation.
Linear list
Linked implementation
Q87. Indicate four characteristics which give rise to variations in IO systems
Data rate, unit oftransfer, operations and error conditions.
Q88. What are principal objectives of an IO SYSTEM?
Objective is to max the CPU utilization, device speed and device independence
Q89. Define access times for a device.
Read write head position time, Transfer time
Q90. What gain is achieved by double buffering as against single buffering?
Increases device efficiency
Q91. What is meant by a special file in UNIX?
Devices are treated as special files in UNIX
Q92. Given disk capacity= 30MB, Block Size=512 bytes, Blocks/cluster=4. Calculate
FAT entries.
14648 approx
Q93. In UNIX link facility several file names link to a single file. What happens if that
file is deleted?
All remaining files need to be deleted before deleting that file.
Q94. Assuming two processes P1 and P2 and resources R! and R2 generate deadlock
condition.
P1->R1,P2->R2,R1<-P1,R2<-P2

13. Q95. How is critical region related to mutual exclusion?
Mutual exclusion is one of the conditions for critical region