Simple Operating System

This project is a simple operating system written in assembly. It includes a bootloader, a protected mode kernel, and a transition to long mode with basic paging. The OS displays "HELLO WORLD" in protected mode and a blue screen in long mode.

Features

• A bootloader that loads the kernel into memory.
• Transition to protected mode and long mode.
• Basic paging setup for identity mapping.
• CPUID and long mode detection.
• Displays "HELLO WORLD" in protected mode.
• Displays a blue screen in long mode.

Requirements

• Assembler: nasm (Netwide Assembler)
• Emulator: qemu-system-x86_64

Install them on Linux:

sudo apt install nasm qemu-system-x86

Project Structure

OS/
├── Makefile                # Build automation
├── build_and_run.sh        # Script to build and run the OS
├── Sector1/                # Bootloader and utility functions
│   ├── bootloader.asm      # Bootloader code
│   ├── DiskRead.asm        # Disk reading function
│   └── print.asm           # Print function for debug messages
├── Sector2+/               # Kernel and supporting files
│   ├── ExtendedProgram.asm # Main kernel code
│   ├── gdt.asm             # Global Descriptor Table setup
│   ├── CPUID.asm           # CPUID and long mode detection
│   └── SimplePaging.asm    # Paging setup for long mode

How to Build and Run

Using the Makefile

1. Build the OS:

   make

2. Run the OS in QEMU:

   make run

3. Clean up build files:

   make clean

Using the Script

1. Run the build and execution script:

   ./build_and_run.sh

Execution Flow

1. Bootloader:

   • Loads the kernel (Extended Program) into memory.
   • Jumps to the kernel at 0x7e00.

2. Kernel:

   • Detects CPUID and long mode support.
   • Transitions to protected mode and sets up the GDT.
   • Sets up paging and transitions to long mode.
   • Displays "HELLO WORLD" in protected mode.
   • Displays a blue screen in long mode.

Debugging

To debug the OS, run QEMU with GDB support:

qemu-system-x86_64 -drive format=raw,file=os-img.bin -boot c -S -gdb tcp::1234

Then connect with GDB:

gdb
target remote localhost:1234

License

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