The Family Computer Disk System (Romanji: Famiri Konpyuta Disuku Shisutemu), Abbrieviated as the Famicom Disk System, FDS, or FCD, was released on February 21, 1986 by Nintendo as a peripheral for the Japanese Nintendo Entertainment System, the Family Computer console in Japan. It uses proprietary floppy disks (called 'Disk Cards') for data storage. It was announced, but never released, for the American and European/Australian Nintendo Entertainment System. Through it's entire production span, 1986-2003, 4.44 million units were sold.
The device is connected to the Famicom deck by plugging in a special cartridge known as the RAM Adapter into the systems cartridge port, and attaching that cartridge's cable to the disk drive. The RAM adapter contains 32 kilobytes (KB) of RAM for temporary program storage, 8 KB of RAM for tile and sprite data storage, and an ASIC known as the 2C33. The ASIC acts as a disk controller for the floppy drive, and also includes additional sound hardware featuring a single-cylce wavetable-lookup synthesizer. Finally, embedded in the 2C33 is an 8KB BIOS ROM. The Disk Cards used are double-sided, with a total capacity of 112 KB per disk. Many games span both sides of a disk, requiring the user to switch sides at some point during gameplay. A few games use two full disks. The Disk System is capable of running on six C-cell batteries or the supplied AC adapter. Batteries usually last five months with daily gameplay. The battery option is due to the likelihood of a standard set of AC plugs already being occupied by a Famicom and a television.