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Family Computer Disk System

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Title Screen

Family Computer Disk System

Also known as: Twin Famicom (Sharp), Famicom Disk System, FDS
Developer: Nintendo R&D2
Publishers: Nintendo (standalone), Sharp (Twin Famicom)
Released in JP: February 21, 1986 (standalone), July 1, 1986 (Twin Famicom)

CopyrightIcon.png This console has hidden developer credits.
DebugIcon.png This console has debugging material.
Carts.png This console has revisional differences.

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The Famicom Disk System was an add-on for the Famicom that utilized distinctive-looking floppy disks (primarily yellow, though sometimes blue) as its media. A number of its games were later ported to the Famicom and/or NES cartridge format, and a number of early Famicom/NES carts were later released (or were planned to be released) in the FDS disk format.

The Twin Famicom, meanwhile, combined the Famicom and FDS into a single unit that supported both formats as well as the Famicom's other peripherals.

One notable aspect of the BIOS itself, which later made cameos in Paper Mario: The Thousand-Year Door and Tetris DS, is the "PLEASE SET DISK CARD" screen: While waiting for the player to insert a disk, Mario and Luigi (using slightly-altered versions of their Mario Bros. sprites) change the color scheme and chase each other around. The FDS' mascot, Diskun, has similarly made cameos in various games.

RAM Check


Hold Start + Select during the boot screen and press Reset. If no problems are detected, the screen will display "PRAM CRAM OK"; if an error occurs, the address of the first memory cell where the error was detected will be displayed.

Programmer Credit

Older Standalone Newer Standalone/Twin Famicom
Fds bios copyright-older.png Fds bios copyright.png

Use the RAM Check code above, but before the text appears on-screen release Start + Select then hold Right + A to see the programmer credit of Takao Sawano. This works on both the standalone unit and the Twin Famicom, the latter of which otherwise makes no reference to Nintendo.

The original version of the standalone BIOS only includes the programmer credit. The newer revision features some space-saving code optimizations (including the removal of the code responsible for adding a drop shadow to the font, seen below) that allowed Sawano to add both the name of the ASIC and the team responsible for FDS development, Nintendo R&D2.

Revisional Differences

Older Standalone Newer Standalone Twin Famicom
Family Computer Disk System-oldertitle.png What system is this, anyway? Who made this, anyway?

Three versions of the FDS BIOS exist. The ones used on the standalone unit display the Nintendo logo, whereas the Twin Famicom uses the "FAMICOM" logo also used on the physical console.

The later revision of the standalone BIOS removed the heavy shading on the bottom edges of the Nintendo logo and the drop shadow behind the alphanumeric character set.