OS from Scratch

This is the branch that pulls the whole atlas together. Building even a tiny OS forces you to use the machine model, C, pointers, assembly, the toolchain, and systems concepts at the same time — there's no runtime to hide behind, because you are writing the runtime. The project is structured as milestones from boot to a working shell.

Tooling decision (fixed): target is x86-64, built with an x86_64-elf cross-compiler and run under QEMU. This is host-agnostic — the same OS boots on an Intel Mac today and on Apple Silicon tomorrow. Every tooling note assumes cross-compiler + QEMU, not ARM bare metal.

Planned milestones

• Setup: an x86_64-elf cross-compiler and QEMU
• The boot process: from BIOS/UEFI to your code
• A minimal bootloader
• Real mode → protected mode → long mode
• A freestanding kernel and the freestanding environment
• Writing to the screen (VGA text / framebuffer)
• The Global Descriptor Table (GDT)
• Interrupts and the Interrupt Descriptor Table (IDT)
• The PIC/APIC and timer interrupts
• Physical memory management
• Paging and virtual memory
• A simple scheduler and task switching
• A simple device driver (keyboard)
• A basic shell

Core sources

• OSDev Wiki — the hub for everything here, including the GCC Cross-Compiler and Bare Bones guides. wiki.osdev.org
• xv6 (MIT) + the xv6 book — the most readable teaching kernel. pdos.csail.mit.edu/6.828/2023/xv6.html
• OSTEP — Operating Systems: Three Easy Pieces (free) — the best OS theory. ostep.org
• Helin & Renberg — The little book about OS development (free) and *Operating Systems: From 0 to 1* (free).
• nanobyte OS (YouTube) — a modern from-scratch series; Intel SDM for protected/long mode; QEMU docs.
• ⚠️ The James Molloy kernel tutorial has known bugs — cite it only with that warning.

Connects to: Systems Programming · Pointers & Memory · Assembly & Compiler Output · Toolchain & Linking