LC

Read the BIOS Memory Map: A20 Line and Reserved Regions

medium4/8

Understand the Reset Vector: Why CPU Starts at 0xFFFFFFF0 Explore the CMOS and RTC: Read System Clock with BIOS INT 0x1A

Language

Compiler

2.0s Limit 256MB

Implementation

Create a program that documents and displays the BIOS memory map.

Requirements:

Define the memory map structure with address ranges and descriptions
Print the complete first 1MB memory layout
Explain the A20 line and why it exists
Show examples of address wrap without A20
Document the display buffer and video memory regions
Explain what happens in each memory region
Include a function to map any address to its region description

Why This Matters

The A20 gate you're studying was originally toggled through the 8042 keyboard controller, a hack so entrenched that Linux's arch/x86/boot/a20.c still ships four different enable methods (keyboard, fast A20 port 0x92, BIOS INT 15h) to cover every motherboard quirk. Getting the memory map wrong here is exactly how real bootloaders corrupt video RAM at 0xB8000 or crash writing into the BIOS ROM shadow region.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0