Sega CD or Mega-CD is an add-onn accessory to Sega Genesis that allowed the use of CD-ROMs and gave a total boost to the console.
Useful info:
Release date: 12 December 1991 in Japan, 15 October 1992 in North America, 2 April 1993 in Europe.
Sega CD can also play audio CDs and CD+G discs
Other enhancements: faster central processing unit, graphic enhancements, greater storage (nearly 320 times larger than Genesis cartridges), support of full motion video (FMV) games
Discontinue date: 1996
Units sold: 2.24 million