Operating system Interview Questions

PREPARED BY PROF S. DAN, RERF, BARRECKPUR Page 1
Operating System
1. Explain the concept of Reentrancy?
It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant
Procedure is one in which multiple users can share a single copy of a program during the same period.
Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each
user process must be stored separately. Thus, the permanent part is the code, and the temporary part
is the pointer back to the calling program and local variables used by that program. Each execution
instance is called activation. It executes the code in the permanent part, but has its own copy of local
variables/parameters. The temporary part associated with each activation is the activation record.
Generally, the activation record is kept on the stack.
Note: A reentrant procedure can be interrupted and called by an interrupting program, and still
execute correctly on returning to the procedure.
2. Explain Belady's Anomaly?
Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process virtual
memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse
happens, i.e., the execution time increases even when more frames are allocated to the process. This
is Belady's Anomaly. This is true for certain page reference patterns.
3. What is a binary semaphore? What is its use?
A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual
exclusion and synchronize concurrent processes.
4. What is thrashing?
It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping
pages, rather than executing instructions. This is due to an inordinate number of page faults.
5. List the Coffman's conditions that lead to a deadlock.
1. Mutual Exclusion: Only one process may use a critical resource at a time.
2. Hold & Wait: A process may be allocated some resources while waiting for others.
3. No Pre-emption: No resource can be forcible removed from a process holding it.
4. Circular Wait: A closed chain of processes exist such that each process holds at least one
resource needed by another process in the chain.
6. What are short, long and medium-term scheduling?
Long term scheduler determines which programs are admitted to the system for processing. It
controls the degree of multiprogramming. Once admitted, a job becomes a process.

Medium term scheduling is part of the swapping function. This relates to processes that are in a
blocked or suspended state. They are swapped out of real-memory until they are ready to execute.
The swapping-in decision is based on memory-management criteria.
Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-
grained decision of which process should execute next. This scheduler is invoked whenever an event
occurs. It may lead to interruption of one process by preemption.
7. What are turnaround time and response time?
Turnaround time is the interval between the submission of a job and its completion. Response time is
the interval between submission of a request, and the first response to that request.
8. What are the typical elements of a process image?
User data: Modifiable part of user space. May include program data, user stack area, and programs
that may be modified.
User program: The instructions to be executed.
System Stack: Each process has one or more LIFO stacks associated with it. Used to store
parameters and calling addresses for procedure and system calls.
Process control Block (PCB): Info needed by the OS to control processes.
9. What is the Translation Lookaside Buffer (TLB)?
In a cached system, the base addresses of the last few referenced pages is maintained in registers
called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most
recently used. Normally, each virtual memory reference causes 2 physical memory accesses- one to
fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is
reduced to just one physical memory access in cases of TLB-hit.
10. What is the resident set and working set of a process?
Resident set is that portion of the process image that is actually in real-memory at a particular instant.
Working set is that subset of resident set that is actually needed for execution. (Relate this to the
variable-window size method for swapping techniques.)
11. When is a system in safe state?
The set of dispatchable processes is in a safe state if there exists at least one temporal order in which
all processes can be run to completion without resulting in a deadlock.
12. What is cycle stealing?
We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller
can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend

operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at
specific break points in an instruction cycle.
13. What is meant by arm-stickiness?
If one or a few processes have a high access rate to data on one track of a storage disk, then they
may monopolize the device by repeated requests to that track. This generally happens with most
common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are
more likely to be affected by this than low density ones.
14. What are the stipulations of C2 level security?
C2 level security provides for:
1. Discretionary Access Control
2. Identification and Authentication
3. Auditing
4. Resource reuse
15. What is busy waiting?
The repeated execution of a loop of code while waiting for an event to occur is called busy-waiting.
The CPU is not engaged in any real productive activity during this period, and the process does not
progress toward completion.
16. Explain the popular multiprocessor thread-scheduling strategies.
1. Load Sharing: Processes are not assigned to a particular processor. A global queue of
threads is maintained. Each processor, when idle, selects a thread from this queue. Note that
load balancing refers to a scheme where work is allocated to processors on a more permanent
basis.
2. Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the
same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way
to reduce synchronization blocking, and minimize process switching. Group scheduling
predated this strategy.
3. Dedicated processor assignment: Provides implicit scheduling defined by assignment of
threads to processors. For the duration of program execution, each program is allocated a set
of processors equal in number to the number of threads in the program. Processors are
chosen from the available pool.
4. Dynamic scheduling: The number of thread in a program can be altered during the course of
execution.
17. When does the condition 'rendezvous' arise?
In message passing, it is the condition in which, both, the sender and receiver are blocked until the
message is delivered.
18. What is a trap and trapdoor?

Trapdoor is a secret undocumented entry point into a program used to grant access without normal
methods of access authentication. A trap is a software interrupt, usually the result of an error
condition.
19. What are local and global page replacements?
Local replacement means that an incoming page is brought in only to the relevant process address
space. Global replacement policy allows any page frame from any process to be replaced. The latter is
applicable to variable partitions model only.
20. Define latency, transfer and seek time with respect to disk I/O.
Seek time is the time required to move the disk arm to the required track. Rotational delay or latency
is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if
any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.
21. Describe the Buddy system of memory allocation.
Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k.
When some memory is required by a process, the block size of next higher order is chosen, and
broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are
called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is
rejoined, and put into the original free-block linked-list.
22. What is time-stamping?
It is a technique proposed by Lamport, used to order events in a distributed system without the use of
clocks. This scheme is intended to order events consisting of the transmission of messages. Each
system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it
increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is
received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value
and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following
rules: For messages x from site i and y from site j, x precedes y if one of the following conditions
holds....(a) if Ti<Tj or (b) if Ti=Tj and i<j.
23. How are the wait/signal operations for monitor different from those for semaphores?
If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So
this allows easier program design. Whereas in semaphores, every operation affects the value of the
semaphore, so the wait and signal operations should be perfectly balanced in the program.
24. In the context of memory management, what are placement and replacement
algorithms?
Placement algorithms determine where in available real-memory to load a program. Common methods
are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process
(or part of a process) needs to be swapped out to accommodate a new program. The replacement
algorithm determines which are the partitions to be swapped out

25. In loading programs into memory, what is the difference between load-time dynamic
linking and run-time dynamic linking?
For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a
target external module causes that module to be loaded and the references are updated to a relative
address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during
execution. Then the correct module is loaded and linked.
26. What are demand-paging and pre-paging?
With demand paging, a page is brought into memory only when a location on that page is actually
referenced during execution. With pre-paging, pages other than the one demanded by a page fault are
brought in. The selection of such pages is done based on common access patterns, especially for
secondary memory devices.
27. Paging a memory management function, while multiprogramming a processor
management function, are the two interdependent?
Yes.
28. What is page cannibalizing?
Page swapping or page replacements are called page cannibalizing.
29. What has triggered the need for multitasking in PCs?
1. Increased speed and memory capacity of microprocessors together with the support fir virtual
memory and
2. Growth of client server computing
30. What are the four layers that Windows NT have in order to achieve independence?
1. Hardware abstraction layer
2. Kernel
3. Subsystems
4. System Services.
31. What is SMP?
To achieve maximum efficiency and reliability a mode of operation known as symmetric
multiprocessing is used. In essence, with SMP any process or threads can be assigned to any
processor.
32. What are the key object oriented concepts used by Windows NT?
Encapsulation, Object class and instance.

33. Is Windows NT a full blown object oriented operating system? Give reasons.
No Windows NT is not so, because its not implemented in object oriented language and the data
structures reside within one executive component and are not represented as objects and it does not
support object oriented capabilities.
34. What is a drawback of MVT?
It does not have the features like
1. ability to support multiple processors
2. virtual storage
3. source level debugging
35. What is process spawning?
When the OS at the explicit request of another process creates a process, this action is called process
spawning.
36. How many jobs can be run concurrently on MVT?
15 jobs.
37. List out some reasons for process termination.
1. Normal completion
2. Time limit exceeded
3. Memory unavailable
4. Bounds violation
5. Protection error
6. Arithmetic error
7. Time overrun
8. I/O failure
9. Invalid instruction
10. Privileged instruction
11. Data misuse
12. Operator or OS intervention
13. Parent termination.
38. What are the reasons for process suspension?
1. swapping
2. interactive user request
3. timing
4. parent process request
39. What is process migration?
It is the transfer of sufficient amount of the state of process from one machine to the target machine.

40. What is mutant?
In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of
ownership.
41. What is an idle thread?
The special thread a dispatcher will execute when no ready thread is found.
42. What is FtDisk?
It is a fault tolerance disk driver for Windows NT.
43. What are the possible threads a thread can have?
1. Ready
2. Standby
3. Running
4. Waiting
5. Transition
6. Terminated
44. What are rings in Windows NT?
Windows NT uses protection mechanism called rings provides by the process to implement separation
between the user mode and kernel mode.
45. What is Executive in Windows NT?
In Windows NT, executive refers to the operating system code that runs in kernel mode.
46. What are the sub-components of I/O manager in Windows NT?
1. Network redirector/ Server
2. Cache manager.
3. File systems
4. Network driver
5. Device driver
47. What are DDks? Name an operating system that includes this feature.
DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT
includes DDks.
48. What level of security does Windows NT meets?
C2 level security.

PROCESS & THREAD CONCEPTS
PROCESS
Overview
Process is program in execution. Process does not meanprogram code. The program code is a
text file which act as a passive entity, which will resides in the disk drives; on the other hand, the
process is active entity which will executes. Their are two types of process –
v User Process
v System Process
User Process execute the user program, on the other hand the system processes are handled by
the operating systemitself.
Process State
As the process executes the states are changing. The states are given below –
v New
v Ready
v Running
v Waiting
v Terminated
As the process executes the process change, its state until it terminates. The states are given
below –
New – The process is created
Ready – The process is waiting for the execution
Running – The process is executing
Waiting – The process moves to running to waiting state if there is any interrupt occurs as I/O
interrupts etc.
Terminated – The process is terminated
Process Control Block
Process control block (PCB) is the main part of any process. PSB will store the all
the necessary information regarding process. The information of the PCB can be different types
few of them are –
v Process State (Whether process is in new, ready, running or waiting state)
v Program counter (Contains the address of the next instruction)
v CPU registers (contains information of accumulator, index register, stack pointer, or different
types of general purpose register)
v CPU-Scheduling information (Contains process priority, and other process parameter)
v Memory Management Information
v Accounting Information
v I/O Status Information
Scheduling Queue
There are different queue for different purpose, which help process scheduling. The different
queues are –
· Job Queue (All the process resides here)
· Ready Queue (Residing in main memory are ready & waiting to execute)
· Device Queue (The process, which switch from running state to waiting state for any interrupt.
Every device have their own device queue)
Job Scheduler

The process migrates from different queue to different queue for the entire life cycle.
The operating systemprovides some technique to schedule the different process
to maximize CPU utilization. For this reason there are different scheduler are present which help
job scheduling. They are –
v Long Term Scheduler or Job Scheduler (Select the process from the job pool and loads them in
the memory for the execution. This scheduler executes frequently. It will help to control the
degree of multiprogramming.)
v Short Term Scheduler (Select the process form ready queue or that are waiting for execute and
allocate them CPU for execution. It runs frequently.)
v Mid Term Scheduler (This will swap any executing process and store them in ready queue for
laterexecution. This is also known as swapping.)
Context Switch
The process mainly uses two different types of resources they are CPU and I/O event. If any
process consist of mainly I/O event the CPU utilization will be less and if a process is mainly
CPU oriented then the I/O resources are wasted. So for maximize CPU utilization the process
should be both CPU and I/O event. To maximize CPU utilizationoperating system provide
Context Switch, in this case theoperating system switch the current executing process by storing
all the necessary information in the PCB and load the new process PCB. Context switch time is
highly dependent upon the hardware. The switching time is nothing but overhead. So to reduce
the time it willmaximize CPU utilization.
Cooperating Process
The process executes in the operating system either independent process or it may be cooperating
process. A process is independent process if it cannot affect another process or another process
does not affect it. On the other hand the cooperating process is if it can affect or being affected
by another process. For many reason the cooperating process are used they are –
v Information Sharing (use of shared file)
v Computation Speedup (break the task into small subparts and executes parallel)
v Modularity
v Convenience
THREADS
Overview
Threads are lightweight process (LWP) which acts as a process. Process creation takes longer
time and take more resources are wasted than thread creation. Threads contains thread id,
program counter, register set all thenecessary information as like as process. For the multithread
programming environment, threads are used. In modern days every operating system are
multithreaded. Take an example of web browser when user view any web page their may
simultaneously work many threads like a thread can be used to download images, other used to
translate the HTML file on the other hand another used for network connection. Therefore, this
multithreading capability provides user convenience. The main advantage of the thread is they
take same memory space as taken by the process. The process can break up into several threads
and every thread can simultaneously work.
Benefit
There are many benefits of multithreading application. Few of them are –
v Responsiveness (Web browser – user interact while other threads done several other things like
downloading image item etc)
v Resource Sharing (Threads share same resources used by the process)

v Economy (Thread creation is easy and take few resources than process creation)
v Utilization of Multiprocessor Architecture (Threads can simultaneously run in different
processor therefore take less time)
Kind of Threads
The threads are mainly classified into two parts they are
v User Thread
v Kernel Thread
The user manages user threads and kernel threads are managed by the operating system itself.
User threads are easy to handle, they are implemented over the thread library at user level. This
thread library creates, managed, and scheduled the user threads in the user space without
intervention of the kernel threads. The drawback is that if kernel is single threaded then any
block system call (by user thread) will block every other thread to execute simultaneously. Ex-
user thread libraries include POSIX P-threads, Mach C-threads and Solaris 2 UI-threads.
On the other hand, kernel threads are create, managed, scheduled by the operating system itself
at the kernel space. The creation & management of kernel threads are slow than the user threads.
Ex-Windows NT, Windows 2000, Solaris 2, BeOS etc supports kernel threads.
Multithreading Model
As many system provides both user & kernel threads so their are many multithreading model,
they are –
v Many-to-One Model (Many user threads maps into one kernel thread. Suffer from block
system call. Ex – Green thread library of Solaris 2.)
v One-to-One Model (Every user threads maps to the single kernel thread. Therefore, every
creation of user thread must create kernel thread. Ex – Windows NT, Windows 2000, OS/2
support this kind of model.)
v Many-to-Many Model (The user threads maps to the many kernel level threads. The no. of
kernel threads same or less than no. of user threads. Ex – Solaris 2, IRIX, HP-UX support this
kind of model)
1) Explain the main purpose of an operating system?
Operating systems exist for two main purposes. One is that it is designed to make sure a
computer system performs well by managing its computational activities. Another is that it
provides an environment for the development and execution of programs.
2) What is demand paging?
Demand paging is a system wherein area of memory that are not currently being used are
swapped to disk to make room for an application’s need.
3) What are the advantages of a multiprocessor system?
With an increased number of processors, there is considerable increase in throughput. It can also
save more money because they can share resources. Finally, overall reliability is increased as
well.

4) What is kernel?
Kernel is the core of every operating system. It connects applications to the actual processing of
data. It also manages all communications between software and hardware components to ensure
usability and reliability.
5) What are real-time systems?
Real-time systems are used when rigid time requirements have been placed on the operation of a
processor. It has well defined and fixed time constraints.
6) What is virtual memory?
Virtual memory is a memory management technique for letting processes execute outside of
memory. This is very useful especially is an executing program cannot fit in the physical
memory.
7) Describe the objective of multiprogramming.
The main objective of multiprogramming is to have process running at all times. With this
design, CPU utilization is said to be maximized.
8 ) What are time sharing systems?
In a Time sharing system, the CPU executes multiple jobs by switching among them, also known
as multitasking. This process happens so fast that users can actually interact with each program
while it is running.
9) What is SMP?
SMP is short for Symmetric MultiProcessing, and is the most common type of multiple-
processor systems. In this system, each processor runs an identical copy of the operating system,
and these copies communicate with one another as needed.
10) How are server systems classified?
Server systems can be classified as either computer-server systems or file server systems. In the
first case, an interface is made available for clients to send requests to perform an action. In the
second case, provisions are available for clients to create, access and update files.

11) What is asymmetric clustering?
In asymmetric clustering, a machine is in a state known as hot standby mode where it does
nothing but to monitor the active server. That machine takes the active server’s role should the
server fails.
12) What is a thread?
A thread is a basic unit of CPU utilization. In general, a thread is composed of a thread ID,
program counter, register set and the stack.
13) Give some benefits of multithreaded programming.
– there is an increased responsiveness to the user
– resource sharing within the process
– economy
– utilization of multiprocessing architecture
14) Briefly explain FCFS.
FCFS is short for First-come, first-served, and is one type of scheduling algorithm. In this
scheme, the process that requests the CPU first is allocated the CPU first. Implementation is
managed by a FIFO queue.
15) What is RR scheduling algorithm?
RR (round-robin) scheduling algorithm is primarily aimed for time-sharing systems. A circular
queue is setup in such a way that the CPU scheduler goes around that queue, allocating CPU to
each process for a time interval of up to around 10 to 100 milliseconds.
16) What necessary conditions can lead to a deadlock situation in a system?
Deadlock situations occur when four conditions occur simultaneously in a system: Mutual
exclusion; Hold and Wait; No preemption; and Circular wait.
17) Enumerate the different RAID levels.
RAID 0 – Non-redundant striping
RAID 1 – Mirrored Disks
RAID 2 – Memory-style error-correcting codes

RAID 3 – Bit-interleaved Parity
RAID 4 – Block-interleaved Parity
RAID 5 – Block-interleaved distributed Parity
RAID 6 – P+Q Redundancy
18) Describe Banker’s algorithm
Bankers Algorithm
Banker’s algorithm is one form of deadlock-avoidance in a system. It gets its name from a
banking system wherein the bank never allocates available cash in such a way that it can no
longer satisfy the needs of all of its customers.
19) What factors determine whether a detection-algorithm must be utilized in a deadlock
avoidance system?
One is that it depends on how often a deadlock is likely to occur under the implementation of this
algorithm. The other has to do with how many processes will be affected by deadlock when this
algorithm is applied.
20) Differentiate logical from physical address space.
Logical address refers to the address that is generated by the CPU. On the other hand, physical
address refers to the address that is seen by the memory unit.
21) How does dynamic loading aid in better memory space utilization?
With dynamic loading, a routine is not loaded until it is called. This method is especially useful
when large amounts of code are needed in order to handle infrequently occurring cases such as
error routines.

22) What are overlays?
Overlays are used to enable a process to be larger than the amount of memory allocated to it. The
basic idea of this is that only instructions and data that are needed at any given time are kept in
memory.
23) What is the basic function of paging?
Paging is a memory management scheme that permits the physical-address space of a process to
be noncontiguous. It avoids the considerable problem of having to fit varied sized memory
chunks onto the backing store.
24) What is fragmentation?
Fragmentation is memory wasted. It can be internal if we are dealing with systems that have
fixed-sized allocation units, or external if we are dealing with systems that have variable-sized
allocation units.
25) How does swapping result in better memory management?
During regular intervals that are set by the operating system, processes can be copied from
main memory to a backing store, and then copied back later. Swapping allows more
processes to be run that can fit into memory at one time.
26) Give an example of a Process State.
– New State – means a process is being created
– Running – means instructions are being executed
– Waiting – means a process is waiting for certain conditions or events to occur
– Ready – means a process is waiting for an instruction from the main processor
– Terminate – means a process is done executing
27) What is a socket?
A socket provides a connection between two applications. Each endpoint of a
communication is a socket.
28) What is Direct Access Method?

Direct Access method is based on a disk model of a file, such that it is viewed as a
numbered sequence of blocks or records. It allows arbitrary blocks to be read or written.
Direct access is advantageous when accessing large amounts of information.
29) When does thrashing occur?
Thrashing refers to an instance of high paging activity. This happens when it is spending
more time paging instead of executing.
30) What is the best page size when designing an operating system?
The best paging size varies from system to system, so there is no single best when it
comes to page size. There are different factors to consider in order to come up with a
suitable page size, such as page table, paging time, and its effect on the overall efficiency
of the operating system.
31) When designing the file structure for an operating system, what attributes are considered?
Typically, the different attributes for a file structure are naming, identifier, supported file
types, and location for the files, size, and level of protection.
32) What is root partition?
Root partition is where the operating system kernel is located. It also contains other
potentially important system files that are mounted during boot time.
33) What are device drivers?
Device drivers provides a standard means of representing I/O devices that maybe
manufactured by different companies. This prevents conflicts whenever such devices are
incorporated in a systems unit.
34) What are the primary functions of VFS?
VFS, or Virtual File System, separates file system generic operations from their
implementation by defining a clean VFS interface. It is also based on a file-representation
structure known as vnode, which contains a numerical designator needed to support
network file systems.
35) What are the different types of CPU registers in a typical operating system design?

– Accumulators
– Index Registers
– Stack Pointer
– General Purpose Registers
36) What is the purpose of an I/O status information?
I/O status information provides info about which I/O devices are to be allocated for a
particular process. It also shows which files are opened, and other I/O device state.
37) What is multitasking?
Multitasking is the process within an operating system that allows the user to run several
applications at the same time. However, only one application is active at a time for user
interaction, although some applications can run “behind the scene”.
38) What are some pros and cons of a command line interface?
A command line interface allows the user to type in commands that can immediately
provide results. Many seasoned computer users are well accustomed to using the
command line because they find it quicker and simpler. The main problem with a command
line interface is that users have to be familiar with the commands, including the switches
and parameters that come with it. This is a downside for people who are not fond of
memorizing commands.
39) What is caching?
Caching is the processing of utilizing a region of fast memory for a limited data and process.
A cache memory is usually much efficient because of its high access speed.
40) What is spooling?
Spooling is normally associated with printing. When different applications want to send an
output to the printer at the same time, spooling takes all of these print jobs into a disk file
and queues them accordingly to the printer.
41) What is an Assembler?
An assembler acts as a translator for low level language. Assembly codes, written using
mnemonic commands are translated by the Assembler into machine language.

42) What are interrupts?
Interrupts are part of a hardware mechanism that sends a notification to the CPU when it
wants to gain access to a particular resource. An interrupt handler receives this interrupt
signal and “tells” the processor to take action based on the interrupt request.
43) What is GUI?
GUI is short for Graphical User Interface. It provides users with an interface wherein actions
can be performed by interacting with icons and graphical symbols. People find it easier to
interact with the computer when in a GUI especially when using the mouse. Instead of
having to remember and type commands, users just click on buttons to perform a process.
44) What is preemptive multitasking?
Preemptive multitasking allows an operating system to switch between software programs.
This in turn allows multiple programs to run without necessarily taking complete control over
the processor and resulting in system crashes.
45) Why is partitioning and formatting a prerequisite to installing an operating system?
Partitioning and formatting creates a preparatory environment on the drive so that the
operating system can be copied and installed properly. This includes allocating space on
the drive, designating a drive name, determining and creating the appropriate file system
structure.
46) What is plumbing / piping?
It is the process of using the output of one program as an input to another. For example,
instead of sending the listing of a folder or drive to the main screen, it can be piped and sent
to a file, or sent to the printer to produce a hard copy.
47) What is NOS?
NOS is short for Network Operating System. It is a specialized software that will allow a
computer to communicate with other devices over the network, including file/folder sharing.
48) Differentiate internal commands from external commands.

Internal commands are built-in commands that are already part of the operating system.
External commands are separate file programs that are stored in a separate folder or
directory.
49) Under DOS, what command will you type when you want to list down the files in a
directory, and at the same time pause after every screen output?
a) dir /w
b) dir /p
c) dir /s
d) dir /w /p
Answer: d) dir /w /p
50) How would a filenamed EXAMPLEFILE.TXT appear when viewed under the DOS
command console operating in Windows 98?
The filename would appear as EXAMPL~1.TXT . The reason behind this is that filenames
under this operating system is limited to 8 characters when working under DOS
environment.

Operating system Interview Questions

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Operating system Interview Questions