The Microvision was the first handheld video-game system with interchangeable cartridges.
Milton Bradley released the Microvision in 1979. Its unusual design placed a small monochrome display in the center of the unit, while each game cartridge included both software and part of the control layout. Players selected games by sliding cartridges into the top of the handheld.
The system predates Nintendo's Game Boy by a decade, but it was much less successful. Only a small number of games were released, and the display and controls were technologically limited. The Microvision is sometimes confused with the Game Boy because both are portable cartridge-based systems, but the Game Boy was a later, more commercially successful product.
Its historical importance comes from combining portability and replaceable games in one device. Later handhelds refined that idea with better screens, stronger processors, and larger libraries.