Hydra OS 🐍

A minimal x86 operating system built from scratch, featuring a custom bootloader pipeline, protected mode initialization, keyboard and framebuffer drivers, interrupt handling, and a built‑in Snake game.

Hydra OS began as a three‑day low‑level programming challenge. The project follows the learning structure from (The Little Book About OS Development) and expands it into a functional monolithic kernel. The long‑term goal is to evolve Hydra OS into a fully usable experimental system. Developers interested in contributing are welcome to fork the repository and open pull requests.

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Overview

Hydra OS is a monolithic kernel written in x86 Assembly and C. It implements the core components required for a minimal operating system:

• Multiboot‑compatible kernel image (ELF)
• GRUB bootloader integration
• Protected mode setup and stack initialization
• Global Descriptor Table (GDT)
• Interrupt Descriptor Table (IDT)
• Keyboard driver (IRQ1)
• Framebuffer text mode driver using VGA memory (0xB8000)
• PIC remapping and interrupt handling
• A minimal interactive shell
• Embedded Snake game rendered directly through the framebuffer

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Features

Bootloader & Initialization

• GRUB loads a compliant multiboot kernel.
• Early Assembly code configures protected mode and stack setup.
• The kernel transitions cleanly into C execution.

Kernel Core

• Monolithic design for simplicity and full hardware control.
• Custom linker script defining memory layout.
• Global Descriptor Table implementation.
• IDT with interrupt stubs and common interrupt handler.

Drivers

• Framebuffer driver: basic character output, cursor positioning, screen clearing, direct memory writes.
• Keyboard driver: scan code reading, character translation, and input dispatching.
• PIC controller: remapping and acknowledgment handling.
• Port I/O utilities: inb, outb for working with hardware ports.

Shell

A simple terminal that supports:

• help – list commands
• clear – reset framebuffer
• echo – print text
• about – kernel/build information
• play – launch Snake game

Snake Game

A framebuffer‑rendered implementation of the classic Snake game:

• Movement with W, A, S, D
• Exit with Q
• Collision detection and game reset

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Project Structure

loader.s                 # Bootloader entry (Multiboot), protected mode setup
link.ld                  # Linker script controlling kernel memory layout
kmain.c                  # Kernel main entry point

fb.c / fb.h              # Framebuffer driver (text mode, VGA memory)
idt.c / idt.h            # Interrupt Descriptor Table setup
idt_asm.s                # Low-level interrupt stubs

gdt.c / gdt.h            # Global Descriptor Table
gdt_asm.s                # Assembly GDT loader

io.s / io.h              # I/O port utilities (inb, outb)
keyboard.c / keyboard.h  # PS/2 keyboard driver
serial.c / serial.h      # Serial COM debugging output

shell.c / shell.h        # Minimal interactive shell
snake.c / snake.h        # Snake game implementation

images/                  # Repository images (banner, assets)
iso/                     # Generated bootable ISO structure
iso/boot/grub/           # GRUB menu configuration (menu.lst)

Makefile                 # Build rules for compiling kernel & ISO
bochsrc.txt              # Bochs emulator configuration
bochslog.txt             # Bochs emulator logs
com1.out                 # Serial console output logs

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Building and Running

Requirements

• GCC with i386 target (or cross‑compiler)
• NASM
• GRUB tools
• xorriso
• Bochs (recommended for testing)

Build

make

Run in Bochs

make run

A bootable ISO file (hydra.iso) will be generated automatically.

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Roadmap

Hydra OS was created in three days as an educational exercise, but the project is intended to grow. Planned additions:

• Complete memory manager
• Basic scheduler and multitasking
• File system support
• Improved terminal and input
• Enhanced framebuffer rendering
• Additional system utilities
• More complete C runtime environment

Contributions are encouraged. The repository is structured to allow incremental improvements.

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Contributing

Contributions of any kind are welcome. If you would like to participate:

1. Fork the repository
2. Create a feature branch
3. Submit a pull request

The aim is to collaboratively build a small but functional operating system grounded in low‑level, educational design.

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Acknowledgements

Hydra OS was developed using concepts and guidance from:

The Little Book About OS Development – https://bit.ly/48JIdWp

This resource provides an excellent foundation for anyone exploring operating system internals.

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Hydra OS is an ongoing experimental project. Further development will continue as time permits, and community contributions are welcomed.