TheOS was my attempt at writing a tiny, portable operating system (before I worked on the real thing at Microsoft).
It was a 32-bit protected mode OS written in C and assembly language.
I’d been fascinated with OS design since my teens, having read many books and papers. I was inspired by microkernel systems like QNX, MicroC/OS II and Amoeba. (I thought Linux had a very crude design; oh well.)
Writing a toy OS falls into the “Ultimately useless, but fun and educational” category.
Watching my laptop boot, then typing words on the screen and seeing them echo across a serial cable to another computer, was pretty neat.
I learned a lot writing TheOS:
- x86 assembly language
- boot loaders
- handle-based resource management
- interrupt service routines
- timers, serial ports, disks, keyboards, displays
- memory management
- data structures
The fun thing about bringing up bare metal (besides making the lights blink) is that you get to do a little bit of everything.
Need printf()? Write it. Need hash tables or a memory manager? Write them. Finally, the chance to use a few chapters from The Art of Computer Programming.
I got as far as booting and launching a couple tasks, basic I/O (keyboard, display, serial port), and was writing the IPC code. I had to stop after joining Microsoft.
