I Built a 64-Bit OS from Scratch: BIOS/UEFI, GUI, Networking, a Browser, and DOOM

AdrianBolt — Thu, 10 Sep 2026 02:29:39 +0000

BoltOS: a from-scratch 64-bit operating system

I built BoltOS as a 64-bit operating system in C and x86-64 assembly, starting with the boot chain rather than an existing kernel or bootloader. It supports both legacy BIOS and UEFI boot paths—no GRUB, no Multiboot, and no external OS libraries.

This is an active project with roughly 41,000 lines of first-party code. I am sharing it to get feedback from people interested in operating systems, systems programming, and bare-metal development.

What is implemented

A custom BIOS MBR and UEFI boot chain that enters a 64-bit higher-half kernel
ACPI, APIC, SMP, preemptive scheduling, ring-3 userland, ELF loading, and syscalls
Physical and virtual memory management, ASLR, SMAP/SMEP, swap, and stack canaries
A graphical desktop with a compositor, window manager, TrueType rendering, clipboard, file manager, IDE, task manager, and 24 apps
Persistent storage through a VFS and block layer, with ATA, AHCI SATA, NVMe, EXT2, and FAT32 support
An in-kernel network stack with DHCP, TCP/UDP, DNS, HTTP, TLS 1.2/1.3, and X.509 verification
A browser engine with a DOM, CSS cascade, box/flex/grid layout, and a from-scratch JavaScript interpreter
A playable DOOM port, audio support, USB HID, and a PE32+ loader for Windows x86-64 console executables

Try it

The first source release is available at BoltOS v0.1.0 — Initial Public Preview.

git clone https://github.com/adriantips/boltossource.git
cd boltossource
bash build.sh
bash run.sh

The repository includes QEMU launchers and a separate UEFI path:

bash run-uefi.sh

I would love feedback on

The boot and kernel architecture
Drivers and hardware coverage
The browser, networking, and userland design
Build reproducibility and documentation

Source and screenshots: https://github.com/adriantips/boltossource

BoltOS: The new era of challenging hobby OS development. (FULL DOOM PORT AND DRIVERS!)

AdrianBolt — Tue, 28 Jul 2026 19:53:06 +0000

Building an operating system from scratch is one of the ultimate challenges for a software engineer. Recently, I came across BoltOS (hosted on GitHub at adriantips/boltossource), a fascinating 64-bit higher-half hobby operating system written entirely in C and Assembly.
Instead of just recycling legacy tutorials, BoltOS aims for a modern environment—skipping old limitations to support advanced hardware and even running Windows binaries natively.
Here is a quick breakdown of what makes this project so cool:
🚀 Technical Highlights
Dual Bootloaders: Supports both a custom legacy BIOS bootloader (entering long mode via unreal mode) and a UEFI bootloader (BOOTX64.EFI) handling GOP and memory maps, mapping the kernel to 0xFFFFFFFF80100000.
Modern Storage Stack: Features a generic block layer with functional drivers for ATA/IDE PIO, AHCI (SATA), and crucially, NVMe (featuring hardware MSI/MSI-X interrupts with polling fallback).
VFS & Persistent Storage: Includes a native RAM file system (BoltFS), read-only EXT2, and read-write FAT32 support where files and user accounts actually survive reboots.
Native PE32+ Executable Loader: One of the wilder features—the kernel can parse PE32+ headers, bind import tables against an in-kernel kernel32 shim, and run real Windows x86-64 console .exe files directly inside the OS!
GUI & TrueType Font Rasterizer: Features a custom windowed GUI powered by a from-scratch TrueType (.ttf) rasterizer that parses bezier outlines, alongside PCI display controller probing (Bochs DISPI/VBE).
Networking & Web Browsing: Packs a network stack, a custom browser engine, and a port of NetSurf.
Of Course... DOOM: It wouldn't be a proper OS project without it. BoltOS successfully runs a port of doomgeneric using a tiny in-house freestanding libc shim.
Check it out
If you are into low-level systems programming, OS dev, or just want to dig into how a hobbyist implements NVMe drivers and Windows binary translation from scratch, check out the repository:
🔗 GitHub: https://github.com/adriantips/boltossource