Dreamcast Visual Memory Unit
Being able to save game progress or character stats had a significant impact on game design. It meant games no longer needed to be completed in a single sitting, instead they could involve complex stories that unfolded after days, weeks or even months of play.
As the Dreamcast used read-only optical discs as its primary distribution media, some form of writable memory was required; SEGA’s solution was the Visual Memory Unit (VMU). But the VMU’s ability to save game progress or character stats was not its most interesting feature. The VMU included a monochrome liquid crystal display (LCD), sound capabilities, a D-Pad, and A and B buttons; making it capable of so much more.
For one it could act as a second screen. In games such as Dino Crisis the VMU showed data about the player’s health. While in multiplayer games, another capability of the VMU was physical linking, such as the NFL 2K series the VMU allowed players to select plays without their opponent seeing.
But more impressively it could independently run mini-games. Sonic Adventure’s Chao Adventure allowed players to transfer eggs to the VMU where they could be hatched and trained, to be stronger and faster, before being introduced back into the Dreamcast game.