Sega Add-On Compact Discs
On December 12th 1991 Sega Japan released an Add-On peripheral for the Megadrive console designed to make use of emerging media formats and also make sure their 16-bit system competed with NEC and Nintendo.
With a CD-ROM as it's storage and format the Mega-CD looked to give Sega fans games up to 320 times bigger than those on cartridge and allow them to experience new techniques like Full Motion Video (FMV). Unleashed on the North American market in October 1992 and in early 1993 for European gamers it never lived up to it's potential from a sales and userbase point of view.
Those who took a chance on this expensive piece of kit however found numerous exceptional games to play.