osdev-boot-sequence

What problem does it solve?

Provides a concise, reliable reference for taking an x86 or x86-64 machine from power-on through firmware handoff into a running kernel, removing guesswork about mode transitions, memory layout, and bootloader expectations.

Core Features & Use Cases

• Firmware-to-kernel flow: Clear BIOS (MBR) and UEFI boot sequences and their differences so you can choose the appropriate strategy.
• Multiboot and headers: Exact Multiboot v1/v2 header placement, checksum rules, and verifier guidance for GRUB-compatible kernels.
• Mode transitions and paging: Step-by-step real→protected→long mode transitions, A20 handling, GDT setup, and higher-half kernel paging/linker layout.
• Use case: Assemble a Multiboot-compliant kernel image, verify header placement, enable A20, set up page tables and GDT, then jump into kernel_main with a correct stack and memory map.

Quick Start

Prepare a kernel binary with a multiboot header in the first 8 KiB, ensure A20 is enabled, load and identity-map low memory, enable protected/long mode as required, and then transfer control to your kernel entry.