 The Sega CD received several variations during its lifetime , of which Sega constructed three . The original model utilized a front @-@ loading motorized disc tray and sat underneath the Genesis . Sega later released the second model of the Sega CD , which was redesigned to sit next to the Genesis console and featured a top @-@ loading disc tray in place of the motorized tray of the original model . In addition to the add @-@ on models , Sega also released the Genesis CDX ( Multi @-@ Mega in Europe ) . This console was a combination of the Genesis and Sega CD into one unit , and initially retailed at US $ 399 . Unique to this model was its additional functionality as a portable compact disc player . 
