LogFAQs > #962151976

They program the game and then upload it to the cartridge using a special USB-A to Cartridge adapter. In the old days, they used other types of ports besides USB-A, but you get the idea. Once that initial cartridge is made, it's known as the "mold cartridge". These sell for top dollar on ebay if you can find them. Once the game is uploaded to the mold cartridge, they put it into a special copier made by Xerox (yes, that Xerox), and punch in the number of copies they want to release. So for example, let's say they're doing a limited edition release based on preorders, maybe they just punch in 1000 and it produces 1000 copies. It takes a while to copy the mold cartridge, and sometimes they run out of materials, so that's usually what causes the delays. The actual game programming itself usually only takes about 6 months, and then the copying is where the real time comes in.

Same sort of deal for compact discs except they use a microscope to write the code onto the disc using microscopic tools (very slow manual process, adds about 6 more months to the release time frame) but once it's there, they just use the same type of Xerox copier to copy the games.