Daniel Etzold, 2016. Boot-sector.
TetrOS is a small Tetris clone written in assembly language. Its code is 446 bytes long: the most a drive’s master boot record allows for the first stage of a boot loader. That makes the whole game fit inside a disk’s 512-byte boot sector.
The PC runs it while starting up, at the point where an operating system would normally begin to load. TetrOS doesn’t need one. Its author points out that this makes TetrOS an operating system itself, which is where the “OS” in its name comes from.
Fitting in so little space meant leaving things out. There are no scores, no intro, no game-over message, no preview of the next brick, and the game never speeds up. To play again, you restart the machine. What remains still has care in it: every brick shape has its own colour, the cursor is hidden, and the next brick is picked at random by a linear congruential generator.