Virtual-Memory-Simulator

Written in Java, it is meant to be a helper in the process of learning how OS manages the memory of the computer.

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1. Project Overview

This Java-based tool simulates the translation of virtual addresses into physical addresses, demonstrating how modern hardware and software coordinate memory access.

Key Objectives:

• Visualize the translation flow from Virtual Addresses to Physical Addresses.
• Demonstrate the role of the TLB (Translation Lookaside Buffer) and Page Table.
• Simulate Page Fault handling and data retrieval from Secondary Storage (Disk).
• Implement and visualize the LRU (Least Recently Used) replacement algorithm for both RAM and TLB.

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2. Key Features

• Parameters of simulation at choice or default: the user can provide his own parameters, but they are verified to be powers of 2.

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• Interactive Address Decomposition: Decomposes user-input virtual addresses into Page Numbers and Offsets.

• Step-by-Step Execution: A "Next Step" mechanism allows users to follow the simulation at their own pace through a snapshot system.

• Real-time Visualization: Graphical displays show the current state of TLB, Page Tables, RAM, and Disk.

• Automated Testing: Features a "Demo Mode" for random or sequential page access sequences.

• Performance Metrics: Real-time monitoring of Hit and Miss rates.

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3. System Architecture

The simulator is built with a modular structure where each class represents a hardware or software entity:

• MemoryManager: Acts as the system controller, orchestrating the translation logic and page fault management.
• TLB: A fast associative cache mapping Page IDs to Frame IDs.
• PageTable: Maps virtual pages to physical frames and tracks state bits like Valid and Dirty.
• PhysicalMemory (RAM): Represents the main memory where active pages are stored in frames.
• Disk: Serves as secondary storage for pages not currently in RAM.
• Replacement: Implements the LRU algorithm to identify victim pages when memory is full.

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4. Technical Implementation

• Language: Java
• UI Framework: Swing (javax.swing)
• Data Structures: Uses Map<Page, Integer> for page tables and Map<Integer, String> for memory storage

Address Translation Logic:

• Page Number = Virtual Address / Page Size
• Offset = Virtual Address % Page Size

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5. Simulation Logic

1. Search TLB: Checks for an immediate mapping. A TLB Hit completes the translation.
2. Search Page Table: On a TLB Miss, the system checks the Page Table for a RAM Hit.
3. Handle Page Fault: If the page is not in RAM, it is fetched from Disk. If RAM is full, the LRU Algorithm selects a page to replace.
4. Update Structures: The TLB and Page Table are updated with the new mapping.
5. LRU Update: The lastTimeUsed timestamp is updated for every access to ensure correct replacement priority.

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6. Installation & Usage

1. Ensure you have the JDK installed.
2. Clone the repository