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It-boots-but-that's-about-it OS

This is me learning a bit of assembly the hard way. I googled "how to write an operating system", found How to write a simple operating system by Mike Saunders et al and am now messing around.

Animated GIF of boots booting

Running boots in the browser with v86


The short answer is "William's computer". Just use my computer, and you'll be fine!

Long answer is probably some combination of these:

  • qemu-system-i386 aka qemu
  • fasm aka flat assembler
  • Windows Subsystem for Linux (bash)
    • some stuff in Ubuntu, like mkisofs, mkfs.msdos etc

Mike's original tutorial used nasm but I found the code worked with fasm just fine and they have a super active forum and is supposedly faster and has a cool macro language. And just generally seems more popular with OS developers, so I'm just following like a lemur lemming, whatever that metaphor is.

How to run (in qemu)


should open up qemu window and print something.

How to run (in Bochs)

Make a floppy image and boot from that in Bochs.


Raw compiled assembly code:


A 1.44Mb floppy disk image (used by the USB step later):


A bootable ISO (untested*):


* Rufus refused to make a USB drive emulating a CD-ROM drive emulating a floppy drive.

How to make a bootable USB flash drive

Safe and slow way

  • Download and run Rufus
  • Under "Device" select the USB flash drive
  • Under "Create a bootable disk using" choose "DD Image"
  • Click the drive icon next to DD Image and choose "myos.bin"
  • Click Start. That should do it.

Fast and scary way

  • Find the exact size of the flash drive in cat /proc/partitions.
  • Copy .env.example to .env and edit the SIZE value. This is a safety feature so I don't accidentally write over the wrong drive, which would be bad.
    ./     # run as Administrator

I've found on Windows you need to be running as root (Administrator) in order to write to the bootloader of a USB drive.


boots is short for "It boots, but that's about it"-OS



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