StringsOS

A bare-metal x86 OS with a hand-written bootloader and kernel, built around an interactive shell for exploring substring-search algorithms.

About

StringsOS is a minimal x86 operating system built from scratch — a 16-bit real-mode bootloader (FASM) that loads a freestanding C++ kernel, which brings up its own IDT/PIC/keyboard driver and runs an interactive shell. The theme of the shell is string processing: at boot you pick between two substring-search algorithms, then use the shell to try them out.

What it does

At boot, the bootloader prompts:

Enter algorithm (bm/std):

• bm — Boyer-Moore string search
• std — naive (brute-force) substring search

The chosen mode is passed to the kernel, which then boots into a shell:

Command	What it does
info	Author, OS, bootloader, compiler, and current search mode
template <text>	Load <text> into memory as the search pattern (also prints the Boyer-Moore shift table when in bm mode)
search <text>	Search <text> for the loaded template using the selected algorithm
upcase <text> / downcase <text> / titlize <text>	Case transforms, printed directly
shutdown	Power off (via ACPI)

Everything — the bootloader, protected-mode switch, GDT, IDT, PIC remapping, PS/2 keyboard scancode handling, VGA text-mode output, and the shell itself — is hand-written, no OS libraries or firmware services beyond BIOS interrupts in the boot sector.

Running it

Docker (recommended — no toolchain to install)

The only non-trivial part of containerizing this is that QEMU normally opens a native GUI window (-display sdl), which a container doesn't have. This setup instead runs QEMU with a VNC display and serves it to your browser via noVNC, so docker compose up is genuinely all you need — no X11/XQuartz setup on the host.

docker compose up --build

Then open http://localhost:6080/vnc.html?autoconnect=true&resize=scale in your browser. Click into the screen to focus it, then type as usual — keyboard and mouse are forwarded over VNC.

Notes:

• The bootloader/kernel toolchain includes FASM, which only ships as a 32-bit x86 binary (no arm64 build) — the image is built for linux/amd64 and runs under emulation on Apple Silicon / arm64 hosts. It's a tiny bare-metal build, so this has no noticeable performance impact.
• To stop: docker compose down.

Natively (Linux/macOS with the toolchain installed)

Requires fasm, a 32-bit-capable g++/ld (gcc-multilib/g++-multilib on Debian/Ubuntu), and qemu-system-i386.

./run.sh --build   # build and run
./run.sh           # run the last build again

This opens QEMU directly in a native SDL window.

Project layout

src/
  bootsect.asm   16-bit real-mode bootloader (FASM): mode prompt, A20, GDT, protected-mode switch, kernel load
  kernel.cpp     freestanding C++ kernel: IDT/PIC/keyboard driver, VGA output, shell, search algorithms
run.sh           native build/run script
Dockerfile       containerized build + QEMU/noVNC runtime
docker-compose.yml

Project status

This project is archived and no longer under active development. Published as-is for reference; issues and PRs may not be reviewed.

License

MIT License