The first model Sega CD had a front tray-loaded CD drive, and connected to the original model Genesis on the underside of the unit. The second model was designed to attach sideways to the second model Genesis, and used a top-loading 'clamshell' style CD drive. Although each model Sega CD was designed to connect to a different model Genesis, they are cross-compatible (although not as asthetically pleasing)
Top Games Label
Vay Lunar: Silver Star Story & Eternal Blue Sonic CD Silpheed Snatcher Shining Force CD Popful Mail Earthworm Jim Ecco: Tides of Time Heart of the Alien: Out of this World Parts I & II The Space Adventure Mickey Mania: The Timeless Adventures of Mickey Mouse