Video games are on carts and CDs - True. They were programed on computers - True. Programs can be made to emulate the console and play the games on a computer rather than a cart - True. People distribute classic Nintendo, Sega, and Arcade games on the internet - True!
Emulators are programs that simulate consoles and allow you to play video games ROMs on your computer for free. This may sound illegal, and it is, but you can still play them if you promise to only evaluate them and delete them after a day. Else your a fugative, even though there is practically no way to track you, or people obsessed enough to track download records of over a thousand emulator sites ^_^
If you're sick of looking everywhere for those Japanese import games of you favorite animes, you can stop looking here!