[MR MAGN3TIC]

How do these ROM download sites manage to get the game off of the cartridge in the first place? For example, if I wanted to rip a ROM from one of my Super Nintendo cartridges to play on an emulator, how would I do it? And would it be illegal?

[KingMike]

Over the years, people dumped all their cartridges and illegally uploaded them to the Internet.
Someone else made a program to catalog all known ROMs.
Someone else used that program to collect every known ROM and shove them into one big zip file.
Some ROM site guy downloaded that big zip file and split it into individual ROM zip files and uploaded them to their site.

There's a number of devices to rip almost any SNES cartridge to a ROM file easily. It's only legal as long as it is used for backup purposes: you don't give the ROM to anyone else, and you delete the ROM if you sell/give away the cart.

[Nightcrawler]

Any device that can read/write the cartridge pins can potentially dump a ROM from the cart. There are a number of devices designed to do just that.