Although this was a peripheral, Sharp released the Twin Famicom (ツインファミコン Tsuinfamikon), a Famicom model that features a built-in Disk System.
- The device was connected to the Famicom deck by plugging a modified cartridge known as the RAM Adapter into the system's cartridge port, which attached via a supplied cable to the disk drive. The RAM adapter contained 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 acted as a disk controller for the floppy drive, and also included additional sound hardware featuring primitive wavetable synthesis and FM synthesis capabilities.
- The Disk System's Disk Cards were somewhat proprietary 2.8 in × 3 in (71 mm × 76 mm) 56K-per-side double-sided floppy. The Disk Cards used were double-sided, with a total capacity of 112 KB per disk. Many games spanned both sides of a disk, requiring the user to switch sides at some point during gameplay. A few games used two full disks (four sides).
- These "Disk Cards," as they are officially called, were a slight modification of Mitsumi's "Quick Disk" 2.8 in (71 mm) square disk format which was used in a handful of Japanese computers and various synthesizer keyboards, along with a few word processors. Some of the QuickDisk drives even made it into devices in Europe and North America, though they were somewhat rare. Mitsumi already had close relations with Nintendo, as it manufactured the Famicom and NES consoles, and possibly other Nintendo hardware.
- The Disk System was capable of running on six C-cell batteries or the supplied AC adapter. Batteries would usually last five months with daily game play. The battery option was included due to the likelihood of a standard set of AC plugs already being occupied by a Famicom and a television.
While the Disk System was years ahead of its time in terms of a disk-format game console, the system and games both have reliability issues. The drive belt in the drive is a proprietary size, since standard floppy drive belts are too large. Until 2004, Japanese residents were able to send their systems to Nintendo directly for repairs/belt replacements, but Nintendo of America and the PAL regions do not service them (as the system was not released in those regions). Due to a flaw in manufacturing, the old belts had a tendency to break, decompose or melt on occasion.
In an effort to save money on production, Nintendo opted to not use disk shutters (a feature seen on 3.5 in (89 mm) floppy disks) to keep dirt out, instead opting to include wax paper sleeves as with the older 5.25 in (133 mm) disks. The only exception to this were certain games that were specially released on blue disks (which did have shutters).
Also, error messages received when attempting to load a disk are unusually simple, to the point where it is difficult to know what the exact problem is. Most in-game error messages during loading are often displayed as 'Err. ##', with ## being the designated number for the type of error message; the most common ones are Err. 02 (the Disk System's batteries being low on power or with no batteries put in altogether), Err. 07 (Side A and B reversed when trying to load the disk), and Err. 27 ('Disk trouble', usually involving the disk surface itself). However, the error messages themselves consist of little explanation (Err. 27, for example, only give the accompanying message 'Disk trouble') and in most cases within gameplay itself, such as Zelda 2, the error message is not given at all, with only the number code shown.