Operating-System-Project

Comprehensive Documentation & Algorithm Guide and Simulation

Table of Contents

1. Project Overview
2. Process Management & Scheduling
3. Memory Management
4. Page Table Management
5. Disk Scheduling
6. Security System

---

1. Project Overview

Project Description

This C++ based Operating System simulation implements core OS concepts including:

• Process scheduling
• Memory allocation and management
• Page table operations
• Disk scheduling
• Security and authentication

System Architecture

graph TD
    A[User Interface] --> B[Security System]
    B --> C[Process Manager]
    B --> D[Memory Manager]
    B --> E[Page Table]
    B --> F[Disk Scheduler]
    C --> G[Round Robin Scheduler]
    D --> H[First Fit Allocator]
    E --> I[Page Allocation]
    F --> J[SCAN Algorithm]

Loading

---

2. Process Management & Scheduling

Round Robin Scheduling Algorithm

Concept

Round Robin is a preemptive scheduling algorithm that assigns a fixed time quantum to each process in a circular queue.

Visual Representation

stateDiagram-v2
    [*] --> Ready
    Ready --> Running: Process Selected
    Running --> Ready: Time Quantum Expired
    Running --> Terminated: Process Complete
    Terminated --> [*]

Loading

How It Works

1. Time Quantum: 2 units
2. Process States:
   • Ready: Waiting for CPU
   • Running: Currently executing
   • Terminated: Execution complete

Example Scenario

gantt
    title Round Robin Scheduling (Time Quantum = 2)
    dateFormat X
    axisFormat %s

    section Process 1
    CPU Burst :0, 2
    Waiting   :2, 4
    CPU Burst :4, 5

    section Process 2
    Waiting   :0, 2
    CPU Burst :2, 4
    CPU Burst :5, 6

    section Process 3
    Waiting   :0, 4
    CPU Burst :4, 5
    CPU Burst :6, 7

Loading

Implementation Highlights

void executeRoundRobin() {
    while (!readyQueue.empty()) {
        Process current = readyQueue.front();
        readyQueue.pop();
        
        // Execute for time quantum
        int executeTime = min(timeQuantum, current.remainingTime);
        current.remainingTime -= executeTime;
        
        // Requeue if not complete
        if (current.remainingTime > 0) {
            readyQueue.push(current);
        }
    }
}

---

3. Memory Management

First Fit Memory Allocation

Concept

First Fit searches from the beginning of memory and allocates the first block that's large enough to accommodate the request.

Visual Representation

graph TD
    subgraph Memory Blocks
        A[Free: 200MB] --> B[Allocated: 300MB]
        B --> C[Free: 400MB]
        C --> D[Allocated: 100MB]
    end

Loading

Memory Block States

stateDiagram-v2
    [*] --> Free
    Free --> Allocated: Memory Request
    Allocated --> Free: Deallocation
    Free --> Split: Large Block
    Split --> Allocated: Use First Part
    Split --> Free: Remaining Part

Loading

Memory Map Example

=== Memory Map ===
Start    Size     Status     Process
0        200MB    Free       N/A
200      300MB    Allocated  Process1
500      400MB    Free       N/A
900      100MB    Allocated  Process2

Implementation Highlights

int allocateMemory(int size, string processName) {
    for (auto& block : memoryBlocks) {
        if (!block.allocated && block.size >= size) {
            // Split if necessary
            if (block.size > size) {
                splitBlock(block, size);
            }
            block.allocated = true;
            block.processName = processName;
            return block.start;
        }
    }
    return -1;
}

---

4. Page Table Management

Virtual Memory Paging

Concept

Maps virtual page numbers to physical frame numbers, managing memory access and protection.

Visual Representation

graph LR
    subgraph Virtual Pages
        VP1[Page 0]
        VP2[Page 1]
        VP3[Page 2]
    end
    subgraph Page Table
        PT1[Entry 0]
        PT2[Entry 1]
        PT3[Entry 2]
    end
    subgraph Physical Frames
        PF1[Frame 0]
        PF2[Frame 1]
        PF3[Frame 2]
    end
    VP1 --> PT1 --> PF2
    VP2 --> PT2 --> PF1
    VP3 --> PT3 --> PF3

Loading

Page Table Entry Structure

struct PageTableEntry {
    int frameNumber;  // Physical frame number
    bool valid;       // Is page in memory?
    bool dirty;       // Has page been modified?
    bool referenced;  // Has page been accessed?
};

Implementation Example

bool allocatePage(int pageNumber) {
    if (freeFrames.empty()) return false;
    
    int frame = freeFrames.back();
    freeFrames.pop_back();
    
    pageTable[pageNumber] = {
        frame,  // frameNumber
        true,   // valid
        false,  // dirty
        false   // referenced
    };
    return true;
}

---

5. Disk Scheduling

SCAN (Elevator) Algorithm

Concept

The disk head moves in one direction servicing requests until it reaches the end, then reverses direction.

Visual Representation

graph TD
    subgraph Disk Track Layout
        T0[Track 0] --> T1[Track 20]
        T1 --> T2[Track 40]
        T2 --> T3[Track 60]
        T3 --> T4[Track 80]
        T4 --> T5[Track 100]
    end
    
    style T2 fill:#ff9999
    style T4 fill:#ff9999

Loading

Head Movement Example

xychart-beta
    title "Disk Head Movement (SCAN)"
    x-axis [0, 20, 40, 60, 80, 100]
    y-axis "Time" 0 --> 5
    line [50, 65, 80, 95, 80, 60, 45, 30]

Loading

Implementation Highlights

vector<int> executeSCAN(bool direction = true) {
    vector<int> sequence;
    vector<int> greater, lesser;
    
    // Sort requests by location
    for (int pos : requests) {
        if (pos >= currentPosition)
            greater.push_back(pos);
        else
            lesser.push_back(pos);
    }
    
    // Build sequence based on direction
    if (direction) {
        sequence = greater + reverse(lesser);
    } else {
        sequence = reverse(lesser) + greater;
    }
    return sequence;
}

---

6. Security System

Role-Based Access Control

Authentication Flow

sequenceDiagram
    participant User
    participant Security
    participant System
    
    User->>Security: Login Request
    Security->>Security: Verify Credentials
    alt Valid Credentials
        Security->>System: Grant Access
        System->>User: Show Menu
    else Invalid Credentials
        Security->>User: Error Message
    end

Loading

Access Levels

graph TD
    A[User Access Levels] --> B[Guest]
    A --> C[User]
    A --> D[Admin]
    B --> E[View Processes]
    C --> E
    C --> F[Basic Operations]
    D --> E
    D --> F
    D --> G[System Management]
    D --> H[User Management]

Loading

Implementation Example

struct User {
    string username;
    string password;
    UserRole role;
};

bool authenticate(string username, string password) {
    for (User& user : users) {
        if (user.username == username && 
            user.password == password) {
            currentUser = &user;
            return true;
        }
    }
    return false;
}

This comprehensive documentation covers all major algorithms and concepts implemented in the project. Each section includes:

• Theoretical explanation
• Visual representation
• Implementation details
• Example scenarios

Read this and enjoy the project.