Kasmon OS — 6.5 KB 32-bit Assembly OS with GUI and Multitasking

[dgt2024]

Hi everyone,

I’m 13 and I’ve been working on Kasmon OS for the past 2 months. It’s a 32-bit operating system written entirely in x86 assembly — no C, no macros, no external frameworks. The kernel is currently 6.5 KB (~1,850 lines).

Some of the features I’ve implemented so far:
- BIOS boot (HDD/FDD, can run on 1 MB drives)
- PS/2 keyboard and mouse drivers
- Preemptive multitasking, even able to interrupt infinite loops (`jmp $`)
- Custom file system (KFS) with folders and a compact file format
- GUI at 1024×768, 8-bit color
- Modular monolithic kernel design

I built everything from scratch to understand how computers really work, and it’s been an incredible learning experience.

GitHub: https://github.com/dgt2024/kadmon
Demo / Updates: https://www.youtube.com/@kasmonos

I’d love any feedback, suggestions, or discussion about design, optimizations, or anything else related to OS development.

[Octocontrabass]

I tried it and it immediately triple faulted. Are you sure you shared the right files?

[ct]

Same here. The supplied boot.bin does not work. Installed fasm and assembled and doesn't work in qemu.

If you try it on real hardware using usb stick then the BIOS might write some data in the boot sector called "BIOS Parameter Block".

That one got me for a while when debugging. Safe is to leave some space for that.

see line 77 and on-wards in https://github.com/calint/pczero/blob/main/src/osca.S for the fix.

Kind regards

[dgt2024]

My apologies

The github unfortunately is outdated, mostly because I'm fixing bugs for the new feature, pre-emptive multitasking.
But I'll update here and on youtube when I finish fixing bugs

Thank you for giving me feedback!

[dgt2024]

If you try it on real hardware using usb stick then the BIOS might write some data in the boot sector called "BIOS Parameter Block".

I checked it out and it's because I'm not using FAT32 or any FAT-like file system, I'm using my own file system, or well, if I have any errors you can tell me.

[ct]

If you try it on hardware with a USB stick the BIOS might write over code in the boot sector located in the specified area.

I am just saying that it got me for a while because I assumed that boot sector is not written to by BIOS after boot - but it does.

Can be a hard to find bug if you try your OS on hardware.

Kind regards