ValcOS

A simple x86 operating system built from scratch for learning and experimentation.

Features

✨ Custom Bootloader - Loads kernel and switches to protected mode
🖥️ VGA Text Mode - 80x25 color display with scrolling
⌨️ Keyboard Driver - Interrupt-driven PS/2 keyboard input
💻 Interactive Shell - Command-line interface with built-in commands
🎨 Color Support - 16-color text output

Prerequisites

• NASM - Netwide Assembler for x86 assembly
• GCC - GNU Compiler Collection (with 32-bit support)
• LD - GNU Linker
• Make - Build automation tool
• QEMU - x86 emulator for testing

Installing Prerequisites on Windows

# Install NASM
winget install nasm.nasm

# Install MinGW (includes GCC, LD, Make)
winget install -e --id GnuWin32.Make

# Install QEMU
winget install -e --id SoftwareFreedomConservancy.QEMU

Quick Start

Building ValcOS

# Clone the repository
cd ValcOS

# Build the OS
make

# Or use the build script
scripts\build.bat

This will create build/ValcOS.img - a bootable 1.44MB disk image.

Running in QEMU

# Run with make
make run

# Or use the run script
scripts\run.bat

# Or manually
qemu-system-x86_64 -drive format=raw,file=build/ValcOS.img

Project Structure

ValcOS/
├── boot/              # Bootloader
│   └── boot.asm       # 16-bit bootloader with protected mode switch
├── kernel/            # Kernel source
│   ├── kernel.c       # Main kernel entry point
│   ├── kernel_entry.asm  # Assembly kernel entry
│   ├── idt.c          # Interrupt descriptor table
│   ├── shell.c        # Command shell
│   └── string.c       # String utilities
├── drivers/           # Device drivers
│   ├── vga.c          # VGA text mode driver
│   └── keyboard.c     # PS/2 keyboard driver
├── include/           # Header files
├── build/             # Compiled binaries
├── scripts/           # Build and run scripts
├── docs/              # Documentation
│   └── ARCHITECTURE.md  # Technical documentation
├── Makefile           # Build system
└── linker.ld          # Linker script

Shell Commands

Once ValcOS boots, you can use these commands:

Command	Description
help	Display available commands
clear	Clear the screen
about	Show OS information
echo <text>	Print text to screen

How It Works

1. BIOS loads the bootloader from the first sector into memory at 0x7C00
2. Bootloader loads the kernel from disk and switches to 32-bit protected mode
3. Kernel initializes VGA display, sets up interrupt handling, and enables the keyboard
4. Shell provides an interactive command-line interface

See ARCHITECTURE.md for detailed technical documentation.

Development

Building Individual Components

# Clean build artifacts
make clean

# Build only
make all

# Build and run
make run

Debugging

To debug with GDB:

# Terminal 1: Start QEMU with GDB server
qemu-system-x86_64 -drive format=raw,file=build/ValcOS.img -s -S

# Terminal 2: Connect GDB
gdb
(gdb) target remote localhost:1234
(gdb) break kernel_main
(gdb) continue

Roadmap

• Bootloader with protected mode
• VGA text mode driver
• Keyboard input
• Basic shell
• Timer/PIT driver
• Memory management (paging, heap)
• Filesystem support (FAT12)
• Multitasking
• System calls
• User mode

Contributing

Contributions are welcome! Feel free to:

• Report bugs
• Suggest features
• Submit pull requests
• Improve documentation

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

Built with passion as a learning project to understand operating system fundamentals.

Resources

• OSDev Wiki - Comprehensive OS development resource
• Intel x86 Manual - Official processor documentation
• NASM Documentation - Assembler reference

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Made with ❤️ for learning and exploration