TetRAM

TetRAM is a small, memory-resident (TSR) Tetris game: working around the single-tasking nature of DOS, it loads itself into RAM and can be started later at any time. The first commercial Tetris had already included such a feature, but this version achieves other goals: a tiny memory footprint (4KB plus change), and the ability to play without suspending the background program.

When invoked (from a 80x25 text-mode screen), the program greys out the current background, and starts a Tetris game on top of it. The familiar rules apply: falling blocks can be moved, rotated and arranged to create solid horizontal lines across the pit; full lines are eliminated, and the pile must be kept from growing all the way to the top.

The game keeps count of completed lines, and the more you score - the faster it gets. Meanwhile the background program continues to run, and can even receive input, except for the four cursor keys used by the game.