ClassicOS

ClassicOS is a 32-bit Intel x86 operating system built from scratch using C, NASM, and GCC. Designed for 386, 486, and Pentium-class CPUs, it runs in protected mode, outputs to VGA text mode and serial ports, and supports floppy/HDD boot with basic FAT support.

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✨ Features

• MBR bootloader at 0x7C00
• Switch to protected mode with GDT
• A20 gate enabling
• Simple FAT12/FAT16 disk loader stub
• VGA text output (0xB8000)
• Serial COM1 support (0x3F8)
• Basic kernel (kmain) written in C
• Makefile-based build system
• Bootable floppy image for testing in QEMU

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⚙️ Requirements

You’ll need the following tools installed:

• nasm
• gcc (targeting i386)
• ld
• make
• qemu-system-i386

Optional:

• gdb
• vncviewer (TigerVNC or similar)

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🛠️ Building ClassicOS

Clone repository:

git clone https://github.com/gbowne1/ClassicOS.git
cd ClassicOS

Run configure script to build a cross-compiler toolchain for i386-elf:

./configure

Source the .build.env file to add the cross-compiler toolchain to your PATH:

source .build.env

Build the kernel:

make