CatOS 🐱

A hardcore, minimalist 16-bit real-mode operating system bootloader written completely from scratch in x86 Assembly.

       /\_/\
      ( o.o )
       > ^ <   [ Meow! CatOS is booting... ]

📝 Description

CatOS is an independent bootloader that takes full control of the CPU immediately after the BIOS POST screen. It does not rely on heavy modern loaders like GRUB or any third-party kernels.

Technical Details:

• 🛠️ Pure Assembly: Written 100% in 16-bit x86 Real Mode NASM.
• ⚡ BIOS Interruption Free: Renders text cleanly without risking typical hardware-specific screen clearing conflicts on custom motherboards.
• 🛑 Safe Halting: Implements a strict cli + hlt loop. It completely disables hardware interrupts, safely freezing the CPU into a absolute zero-power saving state, preventing toxic boot loops.
• 💾 512-Byte Hard Limit: Perfectly optimized to fit into the master boot record (Sector 1) with the mandatory 0xAA55 boot signature.

📁 Project Files

CatOS/
├── .github/
│   └── workflows/
│       └── build.yml       # CI/CD Automated Cloud Build
├── src/
│   ├── api/
│   │   └── io.asm          # I/O functions with conditional inclusion
│   ├── boot.asm            # MBR Bootloader Code (Sector 1)
│   └── kernel.asm          # Main Operating System Kernel Code
├── .gitignore              # Hides compilation binaries & venv
├── LICENSE                 # Project License Terms
├── build.bat               # Windows Universal Lazy Script
├── build.sh                # Linux Universal Lazy Script
└── README.md               # Documentation

⚙️ Installation & Testing

Option 1: Test in Emulator (QEMU)

Make sure NASM and QEMU are added to your System PATH variables, then simply run the universal lazy script:

• Windows: Double-click build.bat
• Linux/macOS: Run ./build.sh

Option 2: Flash onto real hardware (Bare Metal)

1. Go to [Releases] to download the compiled os.img.
2. Open Rufus, select your USB flash drive.
3. Choose os.img (switch filter to "All Files .").
4. Set Partition Scheme to MBR and Target System to BIOS (or UEFI-CSM).
5. Click START, reboot your PC, mash F11 and select the USB drive.

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👤 Author

• FelineFantasy
• License: MIT