Family Computer Disk System

The Family Computer Disk System (also called the Famicom Disk System) is an accessory for the Family Computer. It allowed the Family Computer to play certain games on a proprietary floppy disk format called "Disk Cards" rather than ROM cartridges. Disk Cards had the advantages of being cheaper and allowing for higher data capacity than cartridges at the time. Besides that, the disks were rewritable, making saving easier. Nintendo sought to make Disk Cards a permanent standard for all of their future games at that point, though this plan was abandoned a few years later, due to various issues. Sharp Corporation, a Japanese Electronics and Domestic Appliance company, created the, a Family Computer combined with the Disk System into one piece of hardware, but it was also only released in Japan.

Issues
The main reason why Family Computer Disk System was not released outside Japan and why it eventually lost developer support altogether is believed to be due to a lack of success caused by various issues with the system:
 * The games were easier to pirate, due to the low amount of copy protection (i.e. recognizing legitimate Disk Cards by an empty space on the bottom).
 * The games were easier to damage; Disk Cards, being a form of magnetic media, were sensitive to magnetic wavelengths, and unlike regular 3.5-inch floppy disks, most Disk Cards did not include a shutter to protect the window that exposed the magnetic disk inside (shutters were only included on blue competition cards and gold prize cards). In the latter case, the disk could get scratched, dirty, or even grow mold in severe cases.
 * The system itself was more fragile than the base Famicom, due to the large number of moving parts needed for the disk drive; in particular, the rubber belt that the system used was prone to wearing down much faster than that of a standard floppy disk drive.
 * Because of the enhanced sound qualities, audio was hard to convert when the games were ported to cartridges in the west.
 * The games had lengthy loading times at various points (often when swapping sides, or when entering an area that cannot be processed easily), as magnetic disk drives obtain data by seeking it on the disk rather than instantly pulling it from the memory as a cartridge would.
 * Most games required the player to eject the Disk Card at various points, flip them over, and re-insert them (often after the title screen and on the game's final stretch), similarly to how various PlayStation games require the player to eject and swap optical discs at certain points.
 * The jewel cases that contained the games were smaller than cartridge boxes, and were therefore easier to overlook in stores or lose in homes. The cases were also required to fully protect the Disk Card, whereas cartridges could be stored, standalone, on shelves.
 * The technological superiority of the Disk Card format was short-lived, with higher-capacity cartridges becoming cheaper to produce just a few years later. Combined with the higher rate of piracy that Disk Cards suffered from, this deprived the format of the practicality that served as its primary selling point for developers.

The piracy issue was an especially big problem for Nintendo, and is believed to be the source of their stringent policies regarding copyright protection. It is also widely believed that the Disk System's high piracy rate is what convinced Nintendo to use cartridges for the Nintendo 64 rather than the technologically superior optical discs seen in their rivals, the Sega Saturn and Sony PlayStation.

In 1986, Nintendo sought to counter Disk System piracy by installing special Disk Writer kiosks that would allow consumers to download games onto Disk Card for ¥500 as opposed to the retail price of ¥2,600; some Disk System games were even exclusive to these kiosks. The service was very popular, remaining in place until the Family Computer line's discontinuation in 2003, 9 years after the discontinuation of the Disk System itself.

Trivia

 * Mario and Luigi also appear in the Disk System's BIOS, seen when the Disk System is started. The BIOS also makes a cameo appearance in Paper Mario: The Thousand-Year Door, on Sir Grodus's computer. His computer accepts Data Disks that looks like a Disk Card.
 * When sped up about 16 times, the GameCube menu ambience is revealed to be a slowed-down version of the startup tune for the Disk System BIOS.