Notes, summaries, assignments, exams, and problems for Computers

Operating System Fundamentals

The Operating System (OS) serves several critical roles:

• It acts as a resource manager, controlling access to the hardware.
• It provides an abstraction layer, allowing user processes to call functions that access hardware via system calls.

User Mode vs. Supervisor Mode (Kernel Mode)

The CPU enforces separation between user processes and the OS kernel:

• User Mode: Prohibits privileged instructions.
• Kernel Mode (Supervisor Mode): Allows access to all hardware and privileged operations.

Program Status Word (PSW)

The PSW is a special register holding vital information, such as:

• Access privilege mode.
• Runtime execution conditions (e.g., condition codes).
• Program Counter (PC) and Stack Pointer (SP).

Simplified Interrupt Handling Flow

1. A

Processor & Memory Interface

Processor & Memory Interface: The maximum size of the memory that can be used in any computer is determined by the addressing scheme. For example, a computer that generates 16-bit addresses is capable of addressing up to 2¹⁶ = 65,536 (≈ 64K) memory locations. Machines whose instructions generate 32-bit addresses can utilize a memory that contains up to 2³² = 4,294,967,296 (≈ 4G) locations, whereas machines with 64-bit addresses can access up to 2⁶⁴ ≈ 1.84 × 10¹⁹ locations. The number of locations represents the size of the address space of the computer.

The connection between the processor and its memory consists of address, data, and control lines. The processor uses the address lines to specify the... Continue reading "Processor and Memory Interface: CPU Datapath, Registers & ALU" »

Classes (الصفوف)

• A class consists of variables (fields) and methods.
• Variables are data members of a class.
• Methods are functions that define the class's behavior.

Variables (المتغيرات)

• Declared with a data type and a name.
• Can be public or private.
• Examples: int age, String name.

Methods (الأساليب)

• Functions that perform specific tasks.
• Can have parameters and return values.
• Types:
  • Void methods: Don't return a value.
  • Return type methods: Return a value.
  • Static methods: Can be called without creating an object.
  • Instance methods: Require an object to be called.
  • Abstract methods: Declared without a body; used in abstract classes.
  • Overloaded methods: Multiple methods with the same name but different parameters.

Constructors (البناؤون)

1. Vector Databases — High-Dimensional Embeddings

Store and search high-dimensional vector embeddings. Used in semantic search, similarity search, and RAG pipelines.

Indexing Techniques

• Flat Index (Brute Force) → accurate but slow.
• Approximate Nearest Neighbor (ANN) → fast and scalable.
  • Algorithms: HNSW, FAISS, Annoy.
  • 

3. Retrieval-Augmented Generation (RAG)

Overview

Enhances LLM output by integrating retrieved external knowledge.

• Reduces hallucination and outdated responses.
• Improves factual grounding.

RAG Workflow

1. Indexing: Convert raw data (PDF, HTML, Word) → embeddings.
2. Retrieval: Retrieve relevant document chunks using similarity search.
3. Generation: LLM synthesizes results with the query to produce the final answer.

Retrieval Types

1. Span of Array

Problem Statement:
Find the span of an array (the difference between the maximum and minimum elements).

Example:
Input: [3, 4, 7, 10, 1]
Output: 9 (since 10 - 1 = 9)

Approach:

• Initialize max = -∞ and min = +∞.
• Traverse the array once:
  • Update max if the current element is greater than max.
  • Update min if the current element is less than min.
• Return max - min.

Time Complexity: O(n)
Space Complexity: O(1)

2. Second Largest Element

Problem Statement:
Find the second largest element in an array without sorting it.

Example:
Input: [20, 42, 99, 10, 88, 6]
Output: 88

Approach:

• Initialize two variables: max1 (largest) and max2 (second largest).
• Compare the first two elements to set initial values for max1 and max2.
• From the third element onward, iterate:

1. Why Study Programming Language Concepts?

• Expressiveness: Leverage diverse language features

• Selection: Match language to task (e.g., LISP for AI, PHP for web)

• Learning: Foundations ease uptake of new languages

• Efficiency: Choose constructs (recursion vs. iteration) for performance

• Maintenance: Better code reuse and understanding

2. Programming Domains and Typical Languages

3. Language Categories

• Imperative: Variables + assignment + iteration (C, Java, Python, Perl)

• Functional: Computation

When to Use For Loops vs. While Loops

A for loop and a while loop are both used for iteration in programming, but they serve different purposes and are used in different scenarios. Here are three key points to consider when deciding which loop to use:

• Known vs. Unknown Iterations

  For Loop: Use a for loop when the number of iterations is known beforehand. For example, iterating over a fixed range of numbers or elements in a collection (like an array or list).

  While Loop: Use a while loop when the number of iterations is not known in advance and depends on a condition being met. This is useful for scenarios where you need to continue looping until a specific condition changes (e.g., reading input until a user decides to stop).

• Control Structure Differences

  For

Core OOP Definitions

Class and Object

• Class: A user-defined data structure that binds data members and operations (methods) into a single unit.
• Object: An instance of a class. Objects are used to perform actions or allow interactions based on the class definition.

Variables and Attributes

• Method: An action performed using the object's attributes.
• Attributes: Characteristics or properties of a class. Also known as instance variables (declared outside methods, belonging to one object). They are accessible through static and public methods.
• Class Variable: Declared using the static keyword; shared among all objects of the class.
• Local Variables: Declared inside methods, constructors, or blocks; they exist only while the method runs. They cannot be accessed

PHP Core Concepts: Quick Answers

PHP Array Types

• Indexed Array: A normal array with numeric keys.
• Associative Array: An array with named keys (strings).
• Multidimensional Array: An array containing one or more other arrays.

PHP Arithmetic Operators

• + (Addition): Adds two operands.
• - (Subtraction): Subtracts the second operand from the first.
• * (Multiplication): Multiplies two operands.
• / (Division): Divides the first operand by the second.
• % (Modulus): Returns the remainder of a division.

Understanding PHP Abstract Classes

An abstract class in PHP is a class that cannot be directly instantiated. It may contain abstract methods that must be defined (implemented) in any child classes that inherit from it.

What is a Sticky Form?

A sticky form is a web form that... Continue reading "PHP & Web Development Essentials: Core Concepts" »

Recursive Binary Tree Traversals

Inorder Traversal:

void inorder(struct node *root)
{
  if(root != NULL)
  {
    inorder(root->left);
    printf("%d\t", root->data);
    inorder(root->right);
  }
}

Preorder Traversal:

void preorder(struct node *root)
{
  if(root != NULL)
  {
    printf("%d\t", root->data);
    preorder(root->left);
    preorder(root->right);
  }
}

Postorder Traversal:

void postorder(struct node *root)
{
  if(root != NULL)
  {
    postorder(root->left);
    postorder(root->right);
    printf("%d\t", root->data);
  }
}

Linked List Operations

Search

void search(struct node *head,int key)
{
  struct node *temp = head;
  while(temp != NULL)
  {
    if(temp->data == key)
      printf("key found");
    temp =