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

Operating System Memory Management Fundamentals

The Operating System (OS) is responsible for crucial memory decisions: determining which programs reside in memory, where they are placed, how memory is protected, and what actions to take when memory resources are exhausted.

Parkinson's Law Applied to Computing

Parkinson’s Law states that programs expand to fill the memory available to hold them.

Models for Organizing Memory

Three primary models exist for structuring memory:

• Model A (User on Top, RAM on Bottom):
  • Pros: Fast execution.
  • Cons: No protection (e.g., used in MS-DOS).
• Model B (ROM on Top, User on Bottom):
  • Pros: OS protected.
  • Cons: Slow and not flexible.
• Model C (Drivers at Top, User in Middle, RAM at Bottom):
  • Pros: Fast and secure.
  • Cons: Complex

Software Engineering and Processes

Agile Manifesto

• Individuals/Interactions over Processes
• Working software over documentation
• Collaboration over negotiation
• Responding to change over following a plan

Requirements Engineering

Descriptions of the services that a system should provide and the constraints on its operation.

Functional

What the system should do.

Non-functional

Not directly concerned with the specific services delivered by the system to its users.

Quality Attributes

A scenario describing quality attributes typically involves these elements:

1. Source: Origin of the stimulus.
2. Stimulus: The event arriving.
3. Artifact: Where the event arrives.
4. Environment: Conditions in which the scenario takes place.
5. Response: The result of the event.
6. Response Measure: Must

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