"The original Game Boy was first released in Japan on April 21 1989. Based around a Z80 processor, it has a black and green reflective LCD screen, an eight-way directional pad, two action buttons (A and B), and Start and Select buttons. It plays games from ROM-based media contained in small plastic detachable units called cartridges (sometimes called carts or GamePaks).

The killer game that pushed the Game Boy into the upper reaches of success was Tetris. Tetris was widely popular, and on the handheld format could be played anywhere. It came packaged with the Game Boy, and broadened its reach; adults and kids alike were buying Game Boys in order to play Tetris. Releasing Tetris on the Game Boy was selected as #4 on GameSpy's "25 Smartest Moments in Gaming".

The original Game Boy was the first cartridge-based system that supported more than four players at one time (via the link port). In fact, it has been shown that the system could support 16 simultaneous players at once. However, this feature was only supported in Faceball 2000." (Wikipedia)