The Famicom Disk System is a Japan-only add-on to the popular Nintendo Famicom unit. Colored red and black (to match the Famicom color scheme) the unit attached to the Famicom via the expansion port and allowed games stored on a disk to be played on the unit. Why did Nintendo pursue the use of disks while the rest of the world was limited to game paks? Well, the average Famicom game sold for ¥7000, but for the price of a blank disk and ¥500 gamers could insert a disk into a special unit at stores. This unit would copy the game data files to disk. Furthermore, if you wound up with a dud game on game pak, you were stuck with it unless you could pawn it off on someone else. With a Disk System you could pay another ¥500 and copy a better game over the bad one. Best of all, Disk System games had no need for passwords; your progress was saved right to the disk itself. Plus, oddly enough, the unit ran on C batteries instead of electric power.

As for the disks themselves, they came in two colors - yellow and blue - and measured in at 3" x 4". The orange disks were standard issue, but the five blue ones were meant to be inserted into a Disk Fax unit which would upload your high scores to Nintendo. Contests were frequently held in which the winner would receive special Disk System games that were not available in stores. Furthermore, because the disks did not have a protection mechanism to guard the magnetic film inside the plastic housing, wax paper slips were included with all disks to serve as protection. Disks were to be stored in these slips when not in use. Blank disks cost ¥2000, disks with games already on them cost ¥3000 and included a game manual and colorful game-specific packaging. Just look for Diskun, the system's mascot, when you want to have disk-related fun.

The Disk System was first released in 1985 along with The Legend of Zelda, a killer app which drove sales of the system to over two million within one year. Many classic Nintendo games were released in disk format as well as some rarities that were never converted to cartridge format for release overseas. As technology advanced over the years the 128K capacity of a disk (64K per side) was eclipsed by the storage space of a game pak, so you won't find later Famicom titles such as Super Mario Brothers 3 on the system. Nintendo stopped developing new disk titles and killed the system in 1988 when piracy incidents began to cut into the company's profits. They pulled the system from circulation after 180 titles had been released, although they did keep the disk writers in stores until 1993 and nowadays if you send a disk to Nintendo along with ¥500 and a request they will send you back a disk with your chosen game on it.

Here are titles developed for the system over the years (titles translated to English where possible)...

Do you notice a lack of classic game developers on that list? There's a reason. Nintendo demanded partial copyright over any game published for the Disk System, meaning that publishing a game for the unit caused the developer to lose part of their copyright to Nintendo. Many developers, such as Hudson Soft and Square, declined to work with the the system due to this stipulation and published only to game paks. As for playing games on the system today, they are not all that hard to come by in Japanese used game shops or on eBay. They are not rare in Japan, although overseas you would be hardpressed to find one "in the wild". Certain Nintendo Entertainment System emulators, such as Fwnes or Nesten, are capable of playing the games, but except in the cases of the disk exclusive games you could just track down a game pak of the game you're after. The Famicom Disk System would inspire the Satellaview and the 64DD in future gaming generations.


References:
http://www.planetnintendo.com/nindb/nes.shtml#fcds
http://darkwatcher.psxfanatics.com/console/fds.htm
http://www.atarihq.com/tsr/fds/fds.html
http://nesworld.parodius.com/acc/fdsglist.txt