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README 

        
## Operating System InterviewQuestions



## Microsoft SDE sheet : 



https://docs.google.com/document/d/1uY8U4JFndDC0gDxqrGxQSL5a8EViVy5eKBA8jTQYyNs/edit?usp=sharing

## Gfg Last Minutes Notes:



https://www.geeksforgeeks.org/last-minute-notes-operating-systems/



## Basic OS Interview Questions



### 1.    Why is the operating system important?



### 2.    What's the main purpose of an OS? What are the different types of OS?



### 3.    What are the benefits of a multiprocessor system?



### 4.    What is RAID structure in OS? What are the different levels of RAID configuration?



### 5.    What is GUI?



### 6.    What is a Pipe and when it is used?



### 7.    What are the different kinds of operations that are possible on semaphore?



### 8.    What is a bootstrap program in OS?



### 9.    Explain demand paging?



### 10.    What do you mean by RTOS?



### 11.    What do you mean by process synchronization?



### 12.    What is IPC? What are the different IPC mechanisms?



### 13.    What is different between main memory and secondary memory.



### 14.    What do you mean by overlays in OS?



### 15.    Write top 10 examples of OS?



## Intermediate OS Interview Questions



### 16.    What is virtual memory?



### 17.    What is thread in OS?



### 18.    What is a process? What are the different states of a process?



# Contents



### Intermediate OS Interview Questions (.....Continued)



### 19.    What do you mean by FCFS?



### 20.    What is Reentrancy?



### 21.    What is a Scheduling Algorithm? Name different types of scheduling algorithms.



### 22.    What is the difference between paging and segmentation?



### 23.    What is thrashing in OS?



### 24.    What is the main objective of multiprogramming?



### 25.    What do you mean by asymmetric clustering?



### 26.    What is the difference between multitasking and multiprocessing OS?



### 27.    What do you mean by Sockets in OS?



### 28.    Explain zombie process?



### 29.    What do you mean by cascading termination?



### 30.    What is starvation and aging in OS?



### Advanced OS Interview Questions



### 31.    What do you mean by Semaphore in OS? Why is it used?



### 32.    What is Kernel and write its main functions?



### 33.    What are different types of Kernel?



### 34.    Write difference between micro kernel and monolithic kernel?



### 35.    What is SMP (Symmetric Multiprocessing)?



### 36.    What is a time-sharing system?



### Advanced OS Interview Questions (.....Continued)



### 37.    What is Context Switching?



### 38.    What is difference between Kernel and OS?



### 39.    What is difference between process and thread?



### 40.    What are various sections of the process?



### 41.    What is a deadlock in OS? What are the necessary conditions for a deadlock?



### 42.    What do you mean by Belady’s Anomaly?



### 43.    What is spooling in OS?



##### What do you mean by an operating system? What are its basic



##### functions?



Operating System (OS) is basically a soware program that manages and handles all

resources of a computer such as hardware and soware. The first OS was introduced

in the early 1950s known as GMOs. An OS is responsible for managing, handling, and

coordinating overall activities and sharing of computer resources. It acts as an

intermediary among users of computer and computer hardware.



**Functions of OS:**

There are many functions of the OS. Some of the important functions of OS are given

below:



# Let's get Started



```

Memory and Processor Management

Providing user interface to users

File Management and Device Management

Scheduling of resources and jobs

Error Detection

Security

```



### Basic OS Interview Questions



#### 1.   Why is the operating system important?



OS is the most essential and vital part of a computer without which it is considered

useless. It enables an interface or acts like a link for interaction between computer

soware that is installed on OS and users. It also helps to communicate with

hardware and also maintains balance among hardware and CPU. It also provides

services to users and a platform for programs to run on. It performs all common tasks

applications require.



#### 2.   What's the main purpose of an OS? What are the different



#### types of OS?



The main purpose of an OS is to execute user programs and make it easier for users

to understand and interact with computers as well as run applications. It is specially

designed to ensure that the computer system performs better by managing all

computational activities. It also manages computer memory, processes, and

operation of all hardware and soware.



**Types of OS:**



```

Batched OS (Example: Payroll System, Transactions Process, etc.)

Multi-Programmed OS (Example: Windows O/S, UNIX O/S, etc.)

Timesharing OS (Example: Multics, etc.)

Distributed OS (LOCUS, etc.)

Real-Time OS (PSOS, VRTX, etc.)

```



#### 3.   What are the benefits of a multiprocessor system?



A Multiprocessor system is a type of system that includes two or more CPUs. It

involves the processing of different computer programs at the same time mostly by a

computer system with two or more CPUs that are sharing single memory.



**Benefits:**



```

Such systems are used widely nowadays to improve performance in systems

that are running multiple programs concurrently. 

By increasing the number of processors, a greater number of tasks can be

completed in unit time. 

One also gets a considerable increase in throughput and is cost-effective also as

all processors share the same resources.

It simply improves the reliability of the computer system.

```



#### 4.   What is RAID structure in OS? What are the different levels of



#### RAID configuration?



RAID (Redundant Arrays of Independent Disks) is a method used to store data on

Multiple hard disks therefore it is considered as data storage virtualization

technology that combines multiple hard disks. It simply balances data protection,

system performance, storage space, etc. It is used to improve the overall

performance and reliability of data storage. It also increases the storage capacity of

the system and its main purpose is to achieve data redundancy to reduce data loss.



**Different levels of RAID**



Nowadays, RAID is available in various schemes or RAID level as given below:



```

RAID 0 - Non-redundant striping: This level is used to increase the performance

of the server.

RAID 1 - Mirroring and duplexing: This level is also known as disk mirroring and is

considered the simplest way to implement fault tolerance.

RAID 2 - Memory-style error-correcting codes: This level generally uses dedicated

hamming code parity I.e., a liner form of error correction code.

RAID 3 - Bit-interleaved Parity: This level requires a dedicated parity drive to

store parity information.

RAID 4 - Block-interleaved Parity: This level is similar to RAID 5 but the only

difference is that this level confines all parity data to a single drive.

RAID 5 - Block-interleaved distributed Parity: This level provides far better

performance than disk mirroring and fault tolerance.

RAID 6 - P+Q Redundancy: This level generally provides fault tolerance for two

drive failures.

```



#### 5.   What is GUI?



GUI (Graphical User Interface) is basically a type of user interface that allows users to

use graphics to interact with OS. GUI is created because it is more user-friendly, less

complex, and easier to understand rather than a command-line interface. Its main

goal is to increase efficiency and ease of use. Instead of having to memorize

commands, users can just click on a button to simply execute the procedure.

Examples of GUI include Microso Windows, macOS, Apple’s iOS, etc.



#### 6.   What is a Pipe and when it is used?



The pipe is generally a connection among two or more processes that are

interrelated to each other. It is a mechanism that is used for inter-process

communication using message passing.  One can easily send information such as the

output of one program process to another program process using a pipe. It can be

used when two processes want to communicate one-way i.e., inter-process

communication (IPC).



#### 7.   What are the different kinds of operations that are possible



#### on semaphore?



There are basically two atomic operations that are possible:



```

Wait()

Signal()

```



#### 8.   What is a bootstrap program in OS?



It is generally a program that initializes OS during startup i.e., first code that is

executed whenever computer system startups. OS is loaded through a bootstrapping

process or program commonly known as booting. Overall OS only depends on the

bootstrap program to perform and work correctly. It is fully stored in boot blocks at a

fixed location on the disk. It also locates the kernel and loads it into the main

memory aer which the program starts its execution.



#### 9.   Explain demand paging?



Demand paging is a method that loads pages into memory on demand. This method

is mostly used in virtual memory. In this, a page is only brought into memory when a

location on that particular page is referenced during execution. The following steps

are generally followed:



```

Attempt to access the page.

If the page is valid (in memory) then continue processing instructions as normal.

If a page is invalid then a page-fault trap occurs.

Check if the memory reference is a valid reference to a location on secondary

memory. If not, the process is terminated ( illegal memory access ). Otherwise,

we have to page in the required page.

Schedule disk operation to read the desired page into main memory.

Restart the instruction that was interrupted by the operating system trap.

```



#### 10.   What do you mean by RTOS?



Real Time Operating System (RTOS) is an operating system that is used for real-time

applications i.e., for those applications where data processing should be done in a

fixed and small measure of time. It performs much better on tasks that are needed to

be executed within a short time. It also takes care of execution, monitoring, and all-

controlling processes. It also occupies less memory and consumes fewer resources.



**Types of RTOS:**



```

Hard Real-Time

Firm Real-Time

So Real-Time

```



RTOS is used in Air traffic control systems, Anti-lock Brake Systems, and Heart

pacemakers.



#### 11.   What do you mean by process synchronization?



Process synchronization is basically a way to coordinate processes that use shared

resources or data. It is very much essential to ensure synchronized execution of

cooperating processes so that will maintain data consistency. Its main purpose is to

share resources without any interference using mutual exclusion. There are two

types of process synchronization:



```

Independent Process

Cooperative Process

```



#### 12.   What is IPC? What are the different IPC mechanisms?



IPC (Interprocess Communication) is a mechanism that requires the use of resources

like a memory that is shared between processes or threads. With IPC, OS allows

different processes to communicate with each other. It is simply used for exchanging

data between multiple threads in one or more programs or processes. In this

mechanism, different processes can communicate with each other with the approval

of the OS.



**Different IPC Mechanisms:**



```

Pipes

Message Queuing

Semaphores

Socket

Shared Memory

Signals

```



#### 13.   What is different between main memory and secondary



#### memory.



**Main memory:** Main memory in a computer is RAM (Random Access Memory). It is

also known as primary memory or read-write memory or internal memory. The

programs and data that the CPU requires during the execution of a program are

stored in this memory.

**Secondary memory:** Secondary memory in a computer are storage devices that can

store data and programs. It is also known as external memory or additional memory

or backup memory or auxiliary memory. Such storage devices are capable of storing

high-volume data. Storage devices can be hard drives, USB flash drives, CDs, etc.



```

Primary Memory Secondary Memory

```



```

Data can be directly

accessed by the processing

unit.

```



```

Firstly, data is transferred to

primary memory and aer

then routed to the processing

unit.

```



```

It can be both volatile and

non-volatile in nature.

```



```

It is non-volatile in nature.

```



```

It is more costly than

secondary memory.

```



```

It is more cost-effective or less

costly than primary memory.

```



```

It is temporary because

data is stored temporarily.

```



```

It is permanent because data

is stored permanently.

```



```

In this memory, data can be

lost whenever there is a

power failure.

```



```

In this memory, data is stored

permanently and therefore

cannot be lost even in case of

power failure.

```



```

It is much faster than

secondary memory and

saves data that is currently

used by the computer.

```



```

It is slower as compared to

primary memory and saves

different kinds of data in

different formats.

```



```

It can be accessed by data. It can be accessed by I/O

channels.

```



#### 14.   What do you mean by overlays in OS?



Overlays is basically a programming method that divides processes into pieces so

that instructions that are important and need can be saved in memory. It does not

need any type of support from the OS. It can run programs that are bigger in size than

physical memory by only keeping only important data and instructions that can be

needed at any given time.



#### 15.   Write top 10 examples of OS?



Some of the top OS’s that are used mostly are given below:



```

MS-Windows

Ubuntu

Mac OS

Fedora

Solaris

Free BSD

Chrome OS

CentOS

Debian

Android

```



### Intermediate OS Interview Questions



#### 16.   What is virtual memory?



It is a memory management technique feature of OS that creates the illusion to users

of a very large (main) memory. It is simply space where a greater number of programs

can be stored by themselves in the form of pages. It enables us to increase the use of

physical memory by using a disk and also allows us to have memory protection. It can

be managed in two common ways by OS i.e., paging and segmentation. It acts as

temporary storage that can be used along with RAM for computer processes.



#### 17.   What is thread in OS?



Thread is a path of execution that is composed of a program counter, thread id,

stack, and set of registers within the process. It is a basic unit of CPU utilization that

makes communication more effective and efficient, enables utilization of

multiprocessor architectures to a greater scale and greater efficiency, and reduces

the time required in context switching. It simply provides a way to improve and

increase the performance of applications through parallelism. Threads are

sometimes called **lightweight processes** because they have their own stack but can

access shared data.



Multiple threads running in a process share: Address space, Heap, Static data, Code

segments, File descriptors, Global variables, Child processes, Pending alarms, Signals,

and signal handlers.



Each thread has its own: Program counter, Registers, Stack, and State.



#### 18.   What is a process? What are the different states of a



#### process?



The process is basically a program that is currently under execution. The main

function of an OS is to manage and handle all of these processes. When a program is

loaded into the memory and it becomes a process, it can be divided into four

sections ─ stack, heap, text, and data. There are two types of processes:



```

1. Operating System Processes

2. User Processes

```



**States of Process:**



Different states of the process through which process goes are given below:



```

New State : In this state, a process is just created.

Running: In this state, the CPU starts working on the process’s instructions.

Waiting: In this state, the process cannot run because it just waits for some

event to occur

Ready: In this state, the process has all resources available that are required to

run but it waits to get assigned to a processor because CPUs are not working

currently on instructions passed by the process.

Terminate: In this state, the process is completed I.e., the process has finished

execution.

```



#### 19.   What do you mean by FCFS?



**FCFS** (First Come First Serve) is a type of OS scheduling algorithm that executes

processes in the same order in which processes arrive. In simple words, the process

that arrives first will be executed first. It is non-preemptive in nature. FCFS scheduling

may cause the problem of starvation if the burst time of the first process is the

longest among all the jobs. Burst time here means the time that is required in

milliseconds by the process for its execution. It is also considered the easiest and

simplest OS scheduling algorithm as compared to others. Implementation of FCFS is

generally managed with help of the FIFO (First In First Out) queue.



#### 20.   What is Reentrancy?



Reentrant is simply a function in which various clients can use and shares a single

copy of a program during a similar period. This concept is generally associated with

OS code and does not deal with concurrency. It has two major functions:



```

Program code cannot change or modify itself.

Local data for every client process needs to be stored in different disks.

```



#### 21.   What is a Scheduling Algorithm? Name different types of



#### scheduling algorithms.



A scheduling algorithm is a process that is used to improve efficiency by utilizing

maximum CPU and providing minimum waiting time to tasks. It simply deals with the

problem of deciding which of outstanding requests is to be allocated resources. Its

main aim is to reduce resource starvation and to ensure fairness amongst parties

that are utilizing the resources. In simple words, it is used to allocate resources

among various competing tasks.



**Types of Scheduling Algorithm**



There are different types of scheduling algorithms as given below:



#### 22.   What is the difference between paging and segmentation?



**Paging:** It is generally a memory management technique that allows OS to retrieve

processes from secondary storage into main memory. It is a non-contiguous

allocation technique that divides each process in the form of pages. 

**Segmentation:** It is generally a memory management technique that divides

processes into modules and parts of different sizes. These parts and modules are

known as segments that can be allocated to process.



**Paging Segmentation**



It is invisible to a

programmer.



```

It is visible to a programmer.

```



In this, the size of pages

is fixed.



```

In this, the size of segments is not

fixed.

```



Procedures and data

cannot be separated in

paging.



```

Procedures and data can be

separated in segmentation.

```



It allows a cumulative

total of virtual address

spaces to cross physical

main memory.



```

It allows all programs, data, and

codes to break up into

independent address spaces.

```



It is mostly available on

CPUs and MMU chips.



```

It is mostly available on Windows

servers that may support

backward compatibility, while

Linux has limited support.

```



It is faster for memory

access as compared to

segmentation.



```

It is slower as compared to paging.

```



In this, OS needs to

maintain a free frame.



```

In this, OS needs to maintain a list

of holes in the main memory.

```



In paging, the type of

fragmentation is

internal.



```

In segmentation, the type of

fragmentation is external.

```



The size of the page is

determined by

available memory.



```

The size of the page is determined

by the user.

```



#### 23.   What is thrashing in OS?



It is generally a situation where the CPU performs less productive work and more

swapping or paging work. It spends more time swapping or paging activities rather

than its execution. By evaluating the level of CPU utilization, a system can detect

thrashing. It occurs when the process does not have enough pages due to which the

page-fault rate is increased. It inhibits much application-level processing that causes

computer performance to degrade or collapse.



#### 24.   What is the main objective of multiprogramming?



It refers to the ability to execute or perform more than one program on a single

processor machine. This technique was introduced to overcome the problem of

underutilization of CPU and main memory. In simple words, it is the coordination of

execution of various programs simultaneously on a single processor (CPU). The main

objective of multiprogramming is to have at least some processes running at all

times. It simply improves the utilization of the CPU as it organizes many jobs where

the CPU always has one to execute.



#### 25.   What do you mean by asymmetric clustering?



Asymmetric Clustering is generally a system in which one of the nodes among all

nodes is in hot standby mode whereas the rest of all nodes run different applications.

It simply uses whole or entire hardware resources therefore it is considered a more

reliable system as compared to others.



#### 26.   What is the difference between multitasking and



#### multiprocessing OS?



**Multitasking:** It is a system that allows more efficient use of computer hardware.

This system works on more than one task at one time by rapidly switching between

various tasks. These systems are also known as time-sharing systems.



**Multiprocessing:** It is a system that allows multiple or various processors in a

computer to process two or more different portions of the same program

simultaneously. It is used to complete more work in a shorter period of time.



```

Multitasking Multiprocessing

```



```

It performs more than one

task at a time using a single

processor.

```



```

It performs more than one

task at a time using multiple

processors.

```



```

In this, the number of CPUs is

only one.

```



```

In this, the number of CPUs

is more than one.

```



```

It is more economical. It is less economical.

```



```

It is less efficient than

multiprocessing.

```



```

It is more efficient than

multitasking.

```



```

It allows fast switching among

various tasks.

```



```

It allows smooth processing

of multiple tasks at once.

```



```

It requires more time to

execute tasks as compared to

multiprocessing.

```



```

It requires less time for job

processing as compared to

multitasking.

```



#### 27.   What do you mean by Sockets in OS?



The socket in OS is generally referred to as an endpoint for IPC (Interprocess

Communication). Here, the endpoint is referred to as a combination of an IP address

and port number.  Sockets are used to make it easy for soware developers to create

network-enabled programs. It also allows communication or exchange of

information between two different processes on the same or different machines. It is

mostly used in client-server-based systems.



**Types of Sockets**



There are basically four types of sockets as given below:



```

Stream Sockets

Datagram Sockets

Sequenced Packet Sockets

Raw Sockets

```



#### 28.   Explain zombie process?



Zombie process, referred to as a defunct process, is basically a process that is

terminated or completed but the whole process control block is not cleaned up from

the main memory because it still has an entry in the process table to report to its

parent process. It does not consume any of the resources and is dead, but it still

exists. It also shows that resources are held by process and are not free.



#### 29.   What do you mean by cascading termination?



Cascading termination is a process termination in which if the parent process is

exiting or terminating then the children process will also get terminated. It does not

allow the child to continue processing as its parent process terminates. It is generally

initiated by OS.



#### 30.   What is starvation and aging in OS?



**Starvation:** It is generally a problem that usually occurs when a process has not been

able to get the required resources it needs for progress with its execution for a long

period of time. In this condition, low priority processes get blocked and only high

priority processes proceed towards completion because of which low priority

processes suffer from lack of resources.



**Aging:** It is a technique that is used to overcome the situation or problem of

starvation. It simply increases the priority of processes that wait in the system for

resources for a long period of time. It is considered the best technique to resolve the

problem of starvation as it adds an aging factor to the priority of each and every

request by various processes for resources. It also ensures that low-level queue jobs

or processes complete their execution.



### Advanced OS Interview Questions



#### 31.   What do you mean by Semaphore in OS? Why is it used?



Semaphore is a signaling mechanism. It only holds one positive integer value. It is

simply used to solve the problem or issue of critical sections in the synchronization

process by using two atomic operations i.e., wait() and signal().



**Types of Semaphore**

There are usually two types of semaphores as given below:



```

Binary Semaphore

Counting Semaphore

```



```

Binary Semaphore Mutex

```



```

It allows various process threads

to get the finite instance of the

resource until resources are

available.

```



```

It allows various process

threads to get single

shared resource only at

a time.

```



```

Its functions are based upon

signaling mechanisms.

```



```

Its functions are based

upon a locking

mechanism.

```



```

Binary semaphores are much

faster as compared to Mutex.

```



```

Mutex is slower as

compared to binary

semaphores.

```



```

It is basically an integer. It is basically an object.

```



#### 32.   What is Kernel and write its main functions?



The kernel is basically a computer program usually considered as a central

component or module of OS. It is responsible for handling, managing, and

controlling all operations of computer systems and hardware. Whenever the system

starts, the kernel is loaded first and remains in the main memory. It also acts as an

interface between user applications and hardware.



**Functions of Kernel:**



```

It is responsible for managing all computer resources such as CPU, memory,

files, processes, etc.

It facilitates or initiates the interaction between components of hardware and

soware.

It manages RAM memory so that all running processes and programs can work

effectively and efficiently.

It also controls and manages all primary tasks of the OS as well as manages

access and use of various peripherals connected to the computer.

It schedules the work done by the CPU so that the work of each user is executed

as efficiently as possible.

```



#### 33.   What are different types of Kernel?



There are basically five types of Kernels as given below:



```

Monolithic Kernel

MicroKernel

Hybrid Kernel 

Nano Kernel

Exo Kernel

```



#### 34.   Write difference between micro kernel and monolithic



#### kernel?



**MicroKernel** : It is a minimal OS that executes only important functions of OS. It only

contains a near-minimum number of features and functions that are required to

implement OS. 

Example: QNX, Mac OS X, K42, etc.



**Monolithic Kernel:** It is an OS architecture that supports all basic features of

computer components such as resource management, memory, file, etc. 

Example: Solaris, DOS, OpenVMS, Linux, etc.



```

MicroKernel Monolithic Kernel

```



```

In this soware or program,

kernel services and user

services are present in

different address spaces.

```



```

In this soware or program,

kernel services and user

services are usually present in

the same address space.

```



```

It is smaller in size as

compared to the

monolithic kernel.

```



```

It is larger in size as compared

to a microkernel.

```



```

It is easily extendible as

compared to a monolithic

kernel.

```



```

It is hard to as extend as

compared to a microkernel.

```



```

If a service crashes, it does

affect on working of the

microkernel.

```



```

If a service crashes, the whole

system crashes in a

monolithic kernel.

```



```

It uses message queues to

achieve inter-process

communication.

```



```

It uses signals and sockets to

achieve inter-process

communication.

```



#### 35.   What is SMP (Symmetric Multiprocessing)?



SMP is generally referred to as computer architecture in which the processing of

programs is done by multiple processors that share a common OS and memory. SMP

is very much required if you want to take advantage of multiprocessor hardware. It

simply enables any processor to work on any of the tasks no matter where data or

resources for that particular task are located in memory. These systems are more

reliable than single-processor systems.



#### 36.   What is a time-sharing system?



It is a system that allows more than one user to access the resources of a particular

system in many locations. In simple words, it performs multiple tasks on a single

processor or CPU. As the name suggests, it means to share time into multiple slots in

several processes. It also allows different users from different locations to use a

particular computer system at the same time therefore it is considered one of the

important types of OS.



#### 37.   What is Context Switching?



Context switching is basically a process of saving the context of one process and

loading the context of another process. It is one of the cost-effective and time-saving

measures executed by CPU the because it allows multiple processes to share a single

CPU. Therefore, it is considered an important part of a modern OS. This technique is

used by OS to switch a process from one state to another i.e., from running state to

ready state. It also allows a single CPU to handle and control various different

processes or threads without even the need for additional resources.



#### 38.   What is difference between Kernel and OS?



**Kernel:** Kernel is a system program that controls all programs running on the

computer. The kernel is basically a bridge between the soware and hardware of the

system.



**Operating System:** Operating system is a system program that runs on the computer

to provide an interface to the computer user so that they can easily operate on the

computer.



```

Kernel OS

```



```

It is considered a central

component of OS

```



```

It is considered system soware.

```



```

It is generally

responsible for

converting user

commands into

machine-level

commands.

```



```

It is generally responsible for

managing the resources of

system.

```



```

It simply acts as an

interface between

hardware and

applications.

```



```

It simply acts as an interface

between hardware and user.

```



```

It also performs

functions like process

management, file

management, device

management, I/O

communication, etc.

```



```

It also performs functions like

providing security to data and

files in the the system, providing

access controls to users,

maintaining the system privacy,

etc.

```



```

Its type includes

Microkernel, Monolithic

kernel, etc.

```



```

Its type includes Single and

Multiprogramming batch

systems, Distributed OS, Real-

time OS.

```



#### 39.   What is difference between process and thread?



**Process:** It is basically a program that is currently under execution by one or more

threads. It is a very important part of the modern-day OS.



**Thread:** It is a path of execution that is composed of the program counter, thread id,

stack, and set of registers within the process.



**Process Thread**



It is a computer program

that is under execution.



```

It is the component or entity

of the process that is the

smallest execution unit.

```



These are heavy-weight

operators.



```

These are lightweight

operators.

```



It has its own memory space. It uses the memory of theprocess they belong to.



It is more difficult to create a

process as compared to

creating a thread.



```

It is easier to create a thread

as compared to creating a

process.

```



It requires more resources as

compared to thread.



```

It requires fewer resources as

compared to processes.

```



It takes more time to create

and terminate a process as

compared to a thread.



```

It takes less time to create

and terminate a thread as

compared to a process.

```



It usually run-in separate

memory space.



```

It usually run-in shared

memory space.

```



It does not share data. It shares data with eachother.



It can be divided into

multiple threads.



```

It can’t be further

subdivided.

```



#### 40.   What are various sections of the process?



There are basically four sections in the process as given below:



```

Stack: It is used for local variables and returns addresses. 

Heap: It is used for dynamic memory allocation.

Data : It stores global and static variables.

Code or text: It comprises compiled program code.

```



#### 41.   What is a deadlock in OS? What are the necessary conditions



#### for a deadlock?



Deadlock is generally a situation where a set of processes are blocked as each process

is holding resources and waits to acquire resources held by another process. In this

situation, two or more processes simply try to execute simultaneously and wait for

each to finish their execution because they are dependent on each other. We can see

a hand problem in our system whenever a deadlock occurs in a program. It is one of

the common problems you can see in multiprocessing.



**Necessary Conditions for Deadlock**



There are basically four necessary conditions for deadlock as given below:



```

Mutual Exclusion

Hold and Wait

No Pre-emption

Circular Wait or Resource Wait

```



#### 42.   What do you mean by Belady’s Anomaly?



In the Operating System, process data is loaded in fixed-sized chunks and each chunk

is referred to as a page. The processor loads these pages in the fixed-sized chunks of

memory called frames. Belady’s Anomaly is a phenomenon in which if we increase

the number of frames in memory, then the number of page faults also increases. It is

generally experienced when we use FIFO (First in First out) page replacement

algorithm.



#### 43.   What is spooling in OS?



Spooling simply stands for Simultaneous peripheral operations online. It is referred

to as putting data of various I/O jobs in a buffer. Here, buffer means a special area in

memory or hard disk that can be accessible to an I/O device. It is used for mediation

between a computer application and a slow peripheral. It is very useful and

important because devices access or acquire data at different rates. This operation

also uses disk as a very large buffer and is capable of overlapping I/O operations for

one task with processor operations for another task.