Welcome to the free86 Project repository! free86 is a handcrafted open source operating system for the x86 architecture. This is a hobby project of mine; I primarily target my vintage PC (specs below), but all x86 CPUs after the 80286 should work fine. You can build a bootable floppy image of the system and try it in a VM or on physical hardware.

The system is tested on a vintage PC (1990) with the following specs:

• 30386SX CPU (1988, @16 MHz, 16 MiB address range)
• 640KiB low memory + 4MiB extended memory
• 1 Floppy Drive 3.5", 1.44MiB per disk
• IDE HDD 128MiB

• A 80286 CPU, since it is the first x86 CPU, that supports protected mode.
• The 640KiB onboard memory are enough at the moment.
• VGA support; we use the 640x480 planar mode with 16 active colors and a 256 color palette.

To build the bootable floppy (kickstart image), you first need to compile the custom toolchain.
A Makefile in the Tools directory automates this process. Increasing the number of parallel build jobs can drastically reduce the time needed to build the toolchain, so I highly recommend it. The GNU toolchain is not particularly small, and this tiny tweak can mean a difference between a cigarette break and a leisurely dinner. However, it is not strictly necessary.

# File: Tools/Makefile

# Configure the amount of parallel jobs here
export MAKEFLAGS += -j4

# For example:
# export MAKEFLAGS += -j12

To start building, fire up a terminal, switch to the Tools directory and run make.

cd Tools
make

This will take a while, so feel free to grab a coffee. After the toolchain is built, you can create and run the floppy image with QEMU from within the Source directory.

cd Source
make run-qemu

If you want to tinker with system yourself, I strongly recommended you give the handbook a try. It's not always 100% complete, but I do my best to keep it up to date.

• Special thanks to Damien Guard who generously allowed me to use some of his handmade bitmap fonts. Check out his website, where he provides lots of cool resources.
• David Siñuela Pastor and the other contributors of the MinUnit project, a simple C unit testing framework in a single header file.