The Sega Genesis was a toy computer that plugged into the wall for power, the home television for video, and headphones for audio.
Sonic the Hedgehog is a super fast hedgehog that broke sales records and spun himself off into a franchise that outlived the computer that birthed him and his friends.
Sonic collects rings and stops Dr. Eggman from gathering all the Chaos Emeralds, for who knows what end! When Sonic has all seven chaos emeralds he becomes Super Sonic and gains invulnerability and can go even faster, but he spends the precious rings which guard him. If Sonic runs out of rings and he gets hit just once, he dies.
The Sega Genesis had no memory and couldn't save the state of any games to itself. For Sonic and Tails, this meant any time power was cut to the Genesis, they ceased to exist entirely— from a mathematical computer perspective. The code that will Genesis them again, is stored on the game cartridge itself. When power is restored Sonic and Tails are birthed anew.
This was true for both games Sonic and Sonic 2.
Sonic 2 was the introduction of Super Sonic, with the seven chaos emeralds. The first Sonic game stopped at six and they only served as a 100% completion indicator.
Sonic 3 begins with Super Sonic flying alongside Tails in the Tornado— an airplane Tails designed and engineered— to Angel Island. Shortly after landing on the beach, Knuckles knocks Sonic out of the super state and steals the seven emeralds for Dr. Eggman. But why?
Knuckles is the guardian of the Master Emerald and is the last of the Echidna, the guardian people of the Master Emerald.
As you can see, a handful of pixels of toy characters on a screen controlled by kids using a few molds of plastic and cheap circuit boards, in a game with no dialogue is able to build an immersive world— such that, restricting the lives of our characters to only existing when power is drawn to the Sega Genesis is... artificially constraining.
So Sonic 3 introduced the Master Emerald both in the lore and in the cartridge, effectively becoming an offline computer independent of any given Sega Genesis.
This metaphorical Master Emerald in Sonic 3 has the ability to save game state. Knuckles being from Angel Island has a different story and adventure from Sonic and Tails, which is continued in a fourth and final cartridge designed for the Sega Genesis, the video game and super computer Sonic and Knuckles.
What's a super computer?
Sonic and Knuckles was bottom half ordinary cartridge, top half video game console.
Plugged into a Sega Genesis as usual, this was just one more Sonic game in the franchise. However, with Sonic 3 and the Master Emerald plugged into it, a final chapter in the saga of the emeralds unfolds.
In the Hidden Palace, the sacred chamber with the Master Emerald, the seven Chaos Emeralds charge the Super Emeralds that grant Super Sonic abilities. By merging state between Sonic 3 and Sonic and Knuckles, Sonic may now complete the game as Hyper Sonic— but that's not the final ending.
Remember when Knuckles punched the Chaos Emeralds out of Super Sonic at the beginning of Sonic 3? He was tricked into doing that by Dr. Eggman. To stop him from stealing the Master Emerald for good, Knuckles needs to collect the seven chaos emeralds, use the master emerald to charge the super emeralds, collect the seven super emeralds, become hyper knuckles, defeat Sonic Robotnik powered by the stolen Master Emerald and steal the multiversal terminal Dr. Eggman used to get from earth into the computer in the first place.
Hello. I'm Tyler Childs, Sillyz.Computer entreprenuer. I'm the engineer that's been teamed up with Sonic and his pals ever since we sprung each other from the clutches of Dr. Eggman and his Sega Genesis.