BCS Guruji

Chapter 1: Process Deadlocks

Chapter 2: File system management

Q. List any two file attributes.

Chapter 3: Disk scheduling

Q. List any two disk performance parameters.

Answer: Disk performance parameters are:

1.Seek Time: Time required to move disk arm to required track.

2.Rotational delay: It is a delay caused by rotational movement of the disk platter which is needed to bring the desired data in read/write head. 

3. Transfer time: It is time it takes to read or write data from disk after the head has been positioned over the track.

4. Access Time: Access Time= Seek Time + Rotational Delay + Transfer Rate

5. Disk response time: It is the average time spent by a request waiting to perform its I/O operation. It is average of all response time requests.

Chapter 4: Introduction to distributed operating systems and architecture

Q. Define distributed system.

Answer: A distributed computer system is a system that organizes the computers on a network and communicates and coordinates through message passing. It is a collection of autonomous computers that appear to user as a single computer system.

Chapter 5: Mobile operating system

 Q. What is claim edge?

- 

Q. What is reuqest edge?

Q. Write any two design goals of distributed systems.

Q.What is cluster computing.

Q. What is grid computing?

Q. What is size scalability in distributed system?

Q. What is kernel?

  Syllabus: Chapter 1, Chapter 2 and Chapter 3 half

CHAPTER 1: 

Q. Define Starvation?

- When a process waits for a long time for its resources, then the process is said to be in a situation of starvation.

Q. Explain the term 'select a victim and rollback' in the context of deadlock recovery.

- A. Select a victim: It is the process of selecting the process and resources for pre-emption. It is done based on three criterias- 

1. Priority- Resource of low priority processes will be preempted

2. Own Cost: Process that has completed very less of it's execution will be preempted.

3. Cost affecting other processes: How many maximum process can restart their execution if resources of a particular process P are pre-empted.

-B. Rollback: The process, from which the resources are preempted, will not be able to continue it's execution, such a process is said to be rolled back to some safe state.

Q. Wait for a graph is used for deadlock avoidance in the system. True/False

Q.What is deadlock? State different methods to handle a deadlock.

- Deadlock: A deadlock occurs when a process enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process.

Each process waits for an event that cannot occur, therefore this situation is called as a deadlock.

Q. Explain deadlock prevention strategies.

- There are 4 strategies for deadlock prevention:

1. Eliminate mutual exclusion condition: Mutual exclusion is a condition which says that several process cannot share a single resource at a time. We can eliminate this condition to prevent deadlock. But it cannot be used in all cases, like printers, which cannot print 2 outputs at a time, and hence can handle only one process at a time...

2. Eliminate hold and wait condition: Hold and wait is a condition where a process is holding a resource and also waiting for another requested resource which is being held by some other resource. We can eliminate this condition by either allocating all required resources to the process before it starts its execution, or we can eliminate by not allowing any process to request any more resource until it releases the holded resource.

3. Eliminate No Preemption condition: No preemption is a condition, where if one process is holding a resource then that resource cannot be taken away from that process until the process releases that resource voluntarily. But we can eliminate no preemption only when that resource's working state can be saved and later restored. 

4.Eliminating Circular wait condition:  A circular wait occurs when one or more processes wait in a circular order for the resources they require. It can be eliminated by assigning a priority number to each available resource, and process will be granted that resource only when the priority number of requested resource is higher than currently held resource.

Q. What is a wait-for-graph?

- Wait for graph is a variation of resource allocation graph. It shows the dependency of a process on another process for resource allocation. It only contains process and not the resources. 

Suppose P1->R1 and R1->P2, then there will be edge from P1->P2... 

To detect a deadlock, system needs to maintain a wait for graph and check of cycles in the graph.

As there is a cycle in P1->P2->P4->P1, this is a deadlock situation.

Q. Define request edge and claim edge.

- Request Edge: It is a directed edge from a process to a resource. Pi->Rj is called request edge.

- Claim Edge: It is a dashed line that indicates that process may request a resource in the future. Pi--->Rj

Q. State necessary conditions for deadlock to occur.

- Conditions for deadlock that must hold simultaneously: 

1. Mutual Exclusion: Mutual exclusion is a condition which says that several process cannot share a single resource at a time. Only one process at a time can use a non-shareable resource.

2.Hold and wait condition: Hold and wait is a condition where one resource is waiting to acquire additional resource held by other processes.

3. No-Preemption: Resources allocated to a process cannot be preempted until its completion or released voluntarily by the process holding it.

4. Circular wait condition: The process in a system form a circular list of chain, where each process waits for resource held by another process.

Q. Explain ways for deadlock recovery.

- There are 2 ways for deadlock recovery:

1. Process Termination: There are two methods for terminating processes:

A. Kill all deadlocked proccesses (more expensive method)

B. Kill one process at a time until deadlock is eliminated ( more overhead). The proccess are killed based on cost, priority, etc.

2. Resource Pre-emption: It is a process of pre-empting resources from the other processes one by one and allocate them to other process until deadlock is eliminated.

It has three decisions to be taken:

A. Selecting a process for preemption: A process is selected such that it has low priority, low cost (completed very less of its execution), and how many other process can start after preemption of this process.

B. Rollback: The process from which resources are preempted is said to be roll backed.

C. Prevent Starvation: A process is said to be starving when its waiting for its resources for long time, and this can be eliminated by making sure that a particular process is not selected again and again for preemption/

Numericals:

Q. What is content of need matrix, is the system in safe state? if yes, give the safe sequence.

Q. Is the system deadlocked, if so, which processes are involved.

CHAPTER 2: 

Q. Discuss the various techniques of free space management in file system. 

Q. Explain tree structured directories along with advantages and disadvantages.

Q. What are various dynamic allocation memory management methods.

Q. Give any two disk allocation methods.

: Allocation method is how files are stored in the disk blocks.

There are 3 methods:

1. Contiguous Allocation: 

2. Linked Allocation:

3. Indexed Allocation: 

Q. List any four file attributes.

- Following are file attributes:

1. Name: It is a string of characters.

2. Identifier: It is a tag(a number) that identifies the file in system.

3. Type: It specifies that type of file.

4. Location: It is a pointer to a device and location of file on that device.

5. Size: It is current size of files in bytes or blocks.

Q. Explain different methods for handling free space list in file system.

Q. Explain file operations in detail.

- Following are some file operations:

1. Create Operation: Find a space for new file in system, make an entry for new file in directory and create new file.

2. Write Operation: Perform system call to search file name in directory, find tis location, place the writer pointer to location and update when write occurs.

3. Reading Operation: Perform system call with file name, search in directory, place read pointer to location, update read pointer when read occurs.

4. Reposition or Seek Operation: Search file name in directory, current pointer position is repositioned to given value.

5. Delete Operation: Search file name in directory, release all file space, erase directory entry.

6. Truncate Operation: It is a process to erase contents of file and keep the attributes same expect for file length. So file length becomes zero, and file space is released but file isnt deleted.

7. Open Operation: Perform a system call with file name to open the file before performing any operation.

8. Close Operation: On closing it de-allocates internal descriptors that were created while opening the file.

9. Append Operation: Adds data to end of file.

10. Rename Operation: Used to rename  existing file.

Q. Define acyclic graph directoy.

Q. Define different file access methods.

Q. Newly created directory will have two entries in it. Comment.

Q. What is a bit vector?

Q. Write file access methods.

Answer: There are three file access mechanisms:

1. Sequential Access: Here information of file is processed in order, one record after the other. 

Read next reads next portion of file, write next appends to end of file , and pointer is advanced to new location. Rewinding will reset file pointer to the beginning.

It is simple. But time consuming.

2. Direct Access: Here records are accessed directly. Read n, where file pointer is placed at nth block and reads data of that block. Write n, where operations writes data into nth block.

We can randomly access records.

3. Indexed Access: Index is a seperate file from master file containing key of each record. It is fastest way to access a file. 

- Indexed Sequential: Master file is sorted according to key values. Index table contains only some keys of the records.

- Indexed Non-sequential:  Master file is not in any specified order. There is one entry in index for every record.

 - What is EVM?

Answer: EVM or Ethereum Virtual Machine acts as a computer or runtime environment on Ethereum Network. It's responsible for running and working of smart contracts. Smart contracts are small programs written in Ethereum's language. It helps to run applications on ethereum network.

- Describe EVM with the help of neat diagram.

1) EVM is a decentralized runtime environment that processes and executes smart contracts on the Ethereum blockchain.

2) Universal Computing: It functions like a virtual computer, providing a universal platform for executing code written in Ethereum's smart contract languages, such as Solidity.

3) Consistent Results: EVM ensures that smart contracts produce the same results for all participants across the Ethereum network, maintaining consensus on contract execution.

4) Deterministic Execution: Smart contracts on the EVM execute deterministically, meaning that the same input will always produce the same output, ensuring predictability and reliability.

5) Gas System: EVM uses a gas system to measure and allocate computational resources, preventing abuse and ensuring fair usage of the network by requiring users to pay for the computational work their contracts perform.

This describes a Peer-to-Peer (P2P) network.

 -What is Nonce?

 - Who published a white paper proposing Ethereum in 2013?

 - What is regEx? give example.

import re

# Regular Expression Example

pattern = re.compile(r'\b\d{3}-\d{2}-\d{4}\b')  # Matches social security numbers

text = "John's SSN is 123-45-6789."

match = pattern.search(text)

if match:

    print("SSN found:", match.group())

else:

    print("No SSN found.")

- What is user defined Module? Give example.

# User-Defined Module Example

# Save this code in a file named mymodule.py

def greet(name):

    return f"Hello, {name}!"

# In another script, you can use this module

import mymodule

message = mymodule.greet("Alice")

print(message)

 -What is the use of seek( ) & tell ( ) functions?

seek(offset, whence): Moves the file cursor to the specified offset position, relative to whence (0 for the beginning, 1 for the current position, and 2 for the end).

tell(): Returns the current position of the file cursor.

Write a short note on exception handling.

Exception Handling:

Exception handling in Python allows you to deal with errors or exceptions that may occur during the execution of a program. It involves the use of try, except, else, and finally blocks.

try:

    result = 10 / 0

except ZeroDivisionError:

    print("Cannot divide by zero!")

else:

    print(f"Result: {result}")

finally:

    print("This block always executes.")

 -What is a module? What is package? Explain with example.

Module: A module in Python is a file containing Python definitions and statements. It allows you to logically organize your Python code. For example:

# mymodule.py

def greet(name):

    return f"Hello, {name}!"

# main.py

import mymodule

print(mymodule.greet("Alice"))  # Output: Hello, Alice!

Package: A package is a way of organizing related modules into a single directory hierarchy. It helps in organizing the code and avoids naming conflicts. A package contains an __init__.py file and can have subpackages. Example:

mypackage/

├── __init__.py

├── module1.py

└── module2.py

 Explain any 2 functions in time module.

 --What are the types of file in Python?

- Write the use of seek & tell function.

- How to handle exception in Python?

Q. List out main differences between lists & tuple.

Mutability: Lists are mutable, meaning their elements can be modified after creation. Tuples are immutable, and once created, their elements cannot be changed.

Syntax: Lists are defined using square brackets [], while tuples use parentheses ().

Performance: Tuples generally have better performance than lists, especially in terms of iteration and memory usage.

Methods: Lists have more built-in methods compared to tuples because of their mutability.

Q.  Demonstrate set with example.

# Set Example

fruits = {"apple", "banana", "orange"}

print(fruits)

# Adding an element to the set

fruits.add("grape")

print(fruits)

# Removing an element from the set

fruits.remove("banana")

print(fruits)

- Python is case sensitive language. Comment.
Yes, Python is case-sensitive. Variable names variable and Variable are considered different.

- Write a python program to calculate XY.

# Python Program to Calculate XY

x = 2

y = 3

result = x ** y

print(result)

- Write a python program to accept a number and check whether it is

 perfect number or not.

# Python Program to Check Perfect Number

def is_perfect_number(num):

    divisors_sum = sum(i for i in range(1, num) if num % i == 0)

    return divisors_sum == num

number = int(input("Enter a number: "))

if is_perfect_number(number):

    print(f"{number} is a perfect number.")

else:

    print(f"{number} is not a perfect number.")

-Demonstrate list slicing.

# List Slicing Demonstration

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]

subset = numbers[2:7]  # Elements from index 2 to 6

print(subset)

 -A tuple is ordered collection of items. Comment.
Yes, a tuple is an ordered collection of items. The order of elements in a tuple is preserved.

 -Write a recursive function in Python to display addition of digits in

 single digit.

def sum_digits(n):

    # Base case: single-digit number

    if n < 10:

        return n

    else:

        return sum_digits(sum(map(int, str(n))))

result = sum_digits(12345)

print(f"Sum of digits in single digit: {result}")

 -Write a program in python to accept 'n' integers in a list, compute &

 display addition of all squares of these integers.

n = int(input("Enter the value of n: "))

numbers = [int(input(f"Enter integer {i + 1}: ")) for i in range(n)]

sum_squares = sum(x**2 for x in numbers)

print(f"Addition of squares: {sum_squares}")

- Explain the function enumerate( ).
The enumerate() function in Python is used to iterate over a sequence (such as a list) while keeping track of the index of the current item. It returns pairs of the form (index, value).

-- Explain the extend method of list.

- What are required arguments in function?

- Explain any 2 built-in list functions.

Write a Python program to find GCD of a number using recursion.

 -Give the purpose of selection statements in Python.

 What are the advantages of Python?

Readability and Simplicity: Python code is easy to read and write, making it accessible for beginners and reducing the cost of program maintenance.

Versatility: Python is a versatile language that can be used for web development, data science, artificial intelligence, machine learning, automation, and more.

Large Standard Library: Python comes with a vast standard library that includes modules and packages for a wide range of tasks, eliminating the need for additional downloads.

Object-Oriented Language: Python supports both procedural and object-oriented programming, promoting code reuse and modular design.

 Python is a scripting language. Comment.

Python's concise syntax, ease of use, and the ability to interact with other languages and systems make it well-suited for scripting tasks.

- What is dry run in Python?
A dry run in Python refers to the process of mentally or manually simulating the execution of code without actually running it on a computer. It helps developers understand the flow of the program, identify potential errors, and verify the logic before executing the code.

- Write a short note on datatypes in Python.

Python supports various data types, including:

Numeric Types: Integers, Floats, Complex Numbers

Sequence Types: Strings, Lists, Tuples

Mapping Type: Dictionary

Boolean Type: bool

What is the output of following code :

 def f(X) :

 def  f1(a, b) :

 print ("hello")

 if (b==0) :

   print ("NO")

   return

 return f(a, b)

 return f1

 @ f

 def f(a, b) :

 return a%b

 f(4, 0)

 X = 5

 def  f1( ):

 global X

 X = 4

 f2(a, b) :

 global X

 return a+b+X

f1()

 total = f2(1, 2)

 print (total)

- Define identifiers.

• Write a Python program to check if a given number is Armstrong.
• Write a Python program to check for Zero Division Error Exception.

 List the visualization libraries in python.

1)Matplotlib

2)Seaborn

3)Plotly

4)Bokeh

5)Pyplot

What is the purpose of data visualization?

Data visualization is used to represent data graphically, making complex patterns and trends more understandable. Its purposes include:

Communicating insights effectively

Identifying patterns and outliers

Supporting decision-making

Presenting data in a visually appealing manner.

-Write details notes on basic data visualization tools?

Matplotlib: A popular 2D plotting library for Python.

Seaborn: Built on Matplotlib, it provides a high-level interface for attractive and informative statistical graphics.

Tableau: A powerful and interactive data visualization tool.

-Write the tools used for geospatial data.

ArcGIS: A geographic information system for working with maps and geographic information.

QGIS (Quantum GIS): An open-source alternative for geospatial data analysis 

 - What is missing values?

 -Define standard deviation?