Processors: Z80 8-bit CMOS 4.19 Mhz
Graphics Resolution: 160 x 144
Colours: 4 greys and Gameboy Color 56 on screen, 32,768 total
Sound: 4 channel
Media Format: Cartridge
Control and Input Methods: Built in digital two button gamepad
Nintendo's Gameboy is granddaddy of the handheld console world and in its original, Pocket and Color versions has sold more than any other console, handheld or not. With greyscale graphics and an often difficult to see screen the Gameboy seemed like a non-starter back in 1989 when compared to the colour, backlit and networkable Atari Lynx. But thanks to unbelievable battery life, a keen price and the killer move of bundling it with Tetris, the Gameboy's success was ensured.
Visual Boy Advance - A great Gameboy emulator which also handles the Gameboy Advance.
Official Nintendo Page - Now sadly only dealing with the Gameboy Micro.
Wikipedia Gameboy Page - Extensive info on the Gameboy and its children.