Milton Bradley Microvision

Every earlier game here could only play what was built into it. Milton Bradley's Microvision, released in November 1979 for $49.99, changed that: each game came on a faceplate cartridge that snapped over the screen and carried its own processor, like the Block Buster one fitted here. Engineer Jay Smith, who went on to design the Vectrex, built it around a tiny 16 by 16 LCD grid and a paddle knob at the bottom, making it the first handheld with interchangeable cartridges.