Sonic Jam
"Sonic Jam" is a compilation which contains the four main "Sonic the Hedgehog" games released on the Sega Genesis: "Sonic the Hedgehog", "Sonic the Hedgehog 2", "Sonic the Hedgehog 3", and "Sonic & Knuckles". Unlike future "Sonic" collections, "Sonic Jam" does not use a Genesis emulator; the games are proper ports, and all are nearly identical to the original Sega Genesis releases, with the exception of minor bug fixes. "Sonic Jam" emulates "Sonic & Knuckles" "lock-on technology"—a special feature that allows the player to merge elements of "Sonic & Knuckles" into previous games, resulting in changes to the level design as well as the choice to play as Knuckles the Echidna in "Sonic the Hedgehog 2" and Tails in "Sonic & Knuckles".
Sonic Mega Collection
"Mega Collection" was developed by Sonic Team, the studio behind most games in the "Sonic" series. According to director Yojiro Ogawa, Sonic Team's goal with the compilation was to introduce children to older games in the series and showcase what made "Sonic" successful. Sonic Team chose to focus on including all the Genesis "Sonic" games. Rather than porting them from the Genesis, they collaborated with VR-1 Japan to develop an emulator to run the games' ROM images. Series co-creator Yuji Naka, who served as producer, said the team intended to include the 1993 Sega CD game "Sonic CD", but storage constraints prevented this. Sonic Team also considered including BlueSky Software's "Vectorman" (1995), and "Sonic R" (1997) and "Sonic Shuffle" (2000) were expected to appear in "Mega Collection" at one point. "CD", "Vectorman", and "R" later appeared in "Sonic Gems Collection" (2005), a successor to "Mega Collection" focusing on rare "Sonic" games. Sonic Team had trouble gathering materials for the compilation because it had been a decade since they made the games and "Sega's not that good about keeping history." For instance, Naka wanted to include the original prototype of the first game but Sonic Team could not find its ROM image.