Day 3: Memory Management in Operating Systems

Date: January 15, 2025

Memory management is a fundamental function of operating systems, ensuring efficient allocation, usage, and protection of memory resources. Whether you're preparing for exams, interviews, or building expertise, understanding memory management is crucial.

Goals for the Day

1. Understand the purpose of memory management in an OS.

2. Learn how memory is allocated and managed.

3. Explore concepts like paging, segmentation, and virtual memory.

Topics to Cover

What is Memory Management?

Memory management is the process of controlling and coordinating a computer's memory, assigning portions to processes, and ensuring efficient utilization.

Why is it important?

1. Allows multiple processes to run simultaneously.

2. Optimizes system performance.

3. Prevents memory-related errors like segmentation faults.

Main Functions of Memory Management

1. Allocation and Deallocation:

Assigns memory to processes when needed and reclaims it when no longer in use.

1. Memory Protection:

Prevents processes from accessing memory allocated to others.

1. Memory Mapping:

Maps virtual addresses to physical addresses.

1. Swapping:

Temporarily moves processes between main memory and secondary storage to free up space.

Memory Management Techniques

1. Contiguous Memory Allocation

Memory is allocated in a single continuous block.

Advantages:

Simple implementation.
Disadvantages:

Leads to fragmentation.

1. Paging

Paging divides memory into fixed-sized blocks called pages (in logical memory) and frames (in physical memory).

How it works:

Processes are split into pages.

Pages are mapped to available frames in physical memory using a page table.

Advantages:

Eliminates external fragmentation.

Allows non-contiguous memory allocation.

Disadvantages:

Overhead due to page tables.

1. Segmentation

Memory is divided into segments based on logical divisions like code, data, and stack.

How it works:

Each segment has a base and a limit.

Processes are allocated memory in variable-sized segments.

Advantages:

Provides a logical view of memory.

Better for handling large programs.

Disadvantages:

Can lead to external fragmentation.

Virtual Memory

Virtual memory allows a system to execute processes that are larger than physical memory by using disk space as an extension of RAM.

Key concepts:

Demand Paging: Loads pages into memory only when required.

Page Replacement Algorithms: Determines which page to remove from memory when it's full (e.g., FIFO, LRU, Optimal).

Advantages:

Allows multitasking with limited memory.

Improves system performance by optimizing memory usage.

Disadvantages:

Slower than physical memory due to disk access.

Fragmentation

Fragmentation occurs when memory is inefficiently utilized:

External Fragmentation: Free memory is scattered across non-contiguous blocks.

Internal Fragmentation: Allocated memory exceeds the process requirement, wasting space.

Activities

1. Read/Watch

Read chapters on memory management from Operating System Concepts by Silberschatz or Modern Operating Systems by Tanenbaum.

Watch YouTube tutorials explaining paging, segmentation, and virtual memory.

1. Hands-On Practice

Use commands like free, top, or vmstat in Linux to analyze memory usage.

Experiment with simple paging and segmentation simulations in Java or Python.

Practical Task:

Write a program in C or Python that simulates paging.

Explore how virtual memory works by analyzing the swap space on your system.

Interview Preparation

Common Questions:

1. What is the difference between paging and segmentation?

Paging divides memory into fixed-size blocks, while segmentation divides it into logical sections of variable sizes.

1. Explain virtual memory and its advantages.

Virtual memory uses disk storage as an extension of physical memory, enabling larger processes to run.

1. What are page replacement algorithms?

Algorithms like FIFO and LRU manage memory when a page fault occurs.

Outcome

By the end of Day 3, you should:

1. Understand key memory management techniques like paging and segmentation.

2. Know how virtual memory works and its role in modern operating systems.

3. Be able to explain memory-related concepts in interviews with confidence.

This foundation prepares you for Day 4, where we’ll explore file system management, another critical aspect of operating systems. Let me know if you want further clarification or additional examples!