Page Tables in Operating Systems: Mapping Virtual Addresses to Physical Addresses in Virtual Memory

Learn about page tables and their essential role in managing virtual memory. This tutorial explains how page tables map logical addresses to physical addresses, the process of address translation using the MMU, and the importance of page tables for efficient memory management in operating systems.

Page Tables in Operating Systems

What is a Page Table?

A page table is a crucial data structure used by operating systems to manage virtual memory. It acts as a translator, mapping logical addresses (used by programs) to physical addresses (actual locations in RAM).

Think of it like a phone book: The CPU uses logical addresses (like names in the phone book), and the page table helps it find the corresponding physical address (like phone numbers).

Logical vs. Physical Addresses

• Logical Address: The address used by a program to access data. It's a virtual address, meaning it might not directly correspond to a physical memory location.
• Physical Address: The actual address in RAM where the data is stored. This is what the hardware uses.

Address Translation and the MMU

The CPU generates logical addresses; however, RAM only understands physical addresses. This is where the Memory Management Unit (MMU) comes in. The MMU uses the page table to translate logical addresses into physical addresses.

The logical address is typically split into two parts: a page number and an offset. The page table contains entries that map page numbers to frame numbers in RAM. The offset remains the same in both the logical and physical addresses.

The MMU uses the page number from the logical address to look up the corresponding frame number in the page table. It then combines this frame number with the offset to create the physical address that the RAM uses.

C Code Example: Declaring a Character Variable

char ch = 'a';

Example Output

She said "Hello!" to me.

Next Topic: Mapping from Page Table to Main Memory