Sonic the Hedgehog CD is a 1993 platform game developed and published by Sega for the Sega CD. As Sonic the Hedgehog, the player attempts to protect an extraterrestrial body, Little Planet, from Doctor Robotnik. Like other Sonic games, Sonic runs through themed levels while collecting rings and defeating robots. Sonic CD introduces time travel as a game mechanic. By traveling through time, players can access different versions of stages, featuring alternative layouts, music, and graphics.
Sonic CD director Naoto Ohshima at the 2018 Game Developers Conference
Sonic CD was originally released for the Sega CD (seen here attached below the Genesis).
The Sega CD, known as Mega-CD in most regions outside North America and Brazil, is a CD-ROM accessory for the Sega Genesis produced by Sega as part of the fourth generation of video game consoles. It was released on December 12, 1991, in Japan, October 15, 1992, in North America, and April 2, 1993, in Europe. The Sega CD plays CD games and adds hardware functionality such as a faster CPU and graphic enhancements such as sprite scaling and rotation. It can also play audio CDs and CD+G discs.
Image: Sega CD Model 1 Set
Image: Sega CD Model 2 Set
A model 1 Sega CD without a Genesis attached. The steel joining plate was included to act as RF shielding between the CD and console hardware.
The motherboard and CD laser assembly to a model 2 Sega CD