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Famicom Disk System
The Family Computer Disk System (HVC-022), abbreviated as FDS, Disk System, or Famicom Disk System, is a floppy disk unit peripheral for the Nintendo Family Computer game console, released on February 21, 1986 in Japan.
The Disk System is capable of running on six C-cell batteries or the supplied AC adapter, which is 9V DC, 400mA, with center negative polarity.
RAM Adapter
RAM Adapter
The disk system attaches to the Famicom using a modified cartridge known as the RAM Adapter (HVC-023). The RAM Adapter plugs into the cartridge slot and connects to the FDS through a supplied cable.
The RAM Adapter contains 32KB of RAM for temporary program storage, 8KB 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 primitive wavetable synthesis and FM synthesis capabilities.
RAM Adapter - Bottom
RAM Adapter - Top
Reliability
The FDS and disk cards are notorious for reliability issues, with the most notable being the proprietary drive belt size and absence of shutters on the disk cards (except for a few games that later included them), causing disks to get dirty and data to be corrupted. 
Since Nintendo discontinued servicing FDS drives in the early 2000s, replacing drive belts and calibrating drives is left to those who still want to load games using the disk system. There are only a few guides available that explain how to properly perform a belt replacement, but those usually don’t explain how to correctly calibrate the drive once the new belt has been attached if the user is experiencing disk loading problems. Check out the Belt Replacement and Adjustment Tutorial if you need to replace the belt in your disk system.
Error Codes
When a disk is unable to be correctly read by the system, frustratingly simple and ill-explained error messages are displayed on-screen, leaving the user unsure of the exact problem.
Here’s a list of the FDS Error Codes, which are also used by the MGD1 copier:
Err. 01 = No disk card
Err. 02 = No disk power supply
Err. 03 = Disk card is write protected
Err. 04 = Disk card not authenticated (game maker ID)
Err. 05 = Disk card not authenticated (game name ID)
Err. 06 = Disk card not compatible (version ID)
Err. 07 = Wrong side of disk card set in drive
Err. 08 = Disk card #1 wrong
Err. 09 = Disk card #2 wrong
Err. 10 = Disk card #3 wrong
Err. 20 = Screen data wrong
Err. 21 = Disk card header block (Nintendo-HVC) wrong
Err. 22 = Disk card header block #$01 unrecognized
Err. 23 = Disk card header block #$02 unrecognized
Err. 24 = Disk card header block #$03 unrecognized
Err. 25 = Disk card header block #$04 unrecognized
Err. 26 = Unable to write to disk card
Err. 27 = Block end mark seen but ends prematurely
Err. 28 = File ends prematurely during read
Err. 29 = File ends prematurely during write
Err. 30 = No space left on disk card (full)
Err. 31 = File count in header and number of files on disk card do not match
Nintendo Disk Writer
Disk Writers were available in many toy shops, department stores, and even some convenience stores across Japan until their dismantling in 1993. In most cases, the consumer didn’t actually use these “vending machines.” Instead, you would give your disk to the clerk behind the counter who would operate the machine and give you your disk with a new game written onto it.
Disks and games were available several ways in Disk System land. First, you could buy a blank three-inch disk for 2000 yen and have the game of your choice written onto it for an extra 500 yen. You could use the same disk again and again, writing in different games each time. A game-swap cost only 500 yen, compared for the 5000 yen prices for cartridge-based games of the time. Even after cart technology surpassed the disks, the Disk System remained popular merely for this price factor.
Another way was to buy a disk with the game you wanted already written, complete with manual, for anywhere from 2600 to 3500 yen. These were referred to as “brand new” disks. These disks came in clear hard-plastic cases, and were sold with a manual in another, softer plastic case with a sticker sealing the case shut. If the seal was undamaged, then the disk was considered never used.
Ninety-five percent of games fall into one of these categories. Certain games, mostly 1988-89 era Disk System ports of old Nintendo or Konami-made cartridge games, were available on disk solely via the Disk Writer and could not be purchased on disk separately.
Certain other games, like Topple Zip and Hikaru GENJI: Roller Panic, were sold only by themselves; you couldn’t write them via the Disk Writer. Most of these independent games had cooler packaging than regular cartridge games, and some came with little toys or figures (Roller Panic came in a CD case with a ton of freebies inside). Nintendo was apparently a little more lax in their Disk System packaging guidelines than on regular Famicom cart packaging.
P0rno games were also not sold via the Nintendo-owned Disk Writers. Most titles were sold in record album-style flat cases, but one or two were sold in the traditional Hacker International-style VHS cassette sized plastic case. Hacker reverse-engineered the disk format circa 1988, long before they started releasing Famicom cartridge games of their own. [Source]
What This Site Is
This website is an information repository for those looking to copy, rewrite, or dump FDS games. I decided to create FamicomDiskSystem.com since there is no single English-language reference site dedicated to information about FDS copying, dumping, and writing. Additionally, since Nintendo no longer supports the rewriting or selling of disk cards, the magnetic disk media will slowly degrade and lose magnetic charge over time, rendering the FDS disks unplayable. The information on this site will allow you to successfully copy, dump, and rewrite your games onto FDS disks to enjoy them for decades to come.
What This Site Is Not
This site is not a piracy or warez website, and the information presented here is not to be used for game piracy.
Furthermore, I am not able to assist you with every question. Please use my resources to find what you are looking for.
About the Author
I have been an avid Famicom enthusiast and collector since 2006. I write nearly all of my tutorials and information and take the majority of pictures and screenshots you see on the site. Proper credit is given to collaborators and other credit-worthy individuals who have helped me along the way.
