a peripheral for the Nintendo Family Computer console in Japan. It uses proprietary floppy disks (called "Disk Cards") for data storage. It was announced, but not released, for the North American/PAL Nintendo Entertainment System. Through its entire production span, 1986–2003, 4.44 million units were sold.
The device is connected to the Famicom deck by plugging a special cartridge known as the RAM Adapter into the system's cartridge port, and attaching that cartridge's cable to the disk drive.
Source: Wikipedia, "Family Computer Disk System", available under the CC-BY-SA License.