It has been assumed that certain design choices for the NES were influenced by the potential to add a disk system to the unit. The expansion port on the bottom of the NES was one indication that a Disk System was planned, but how would it have looked and worked?
Physically, the disk system would have had to come in two pieces. The first would have been a RAM adapter, which would look like a typical NES Game Pak and function just like the Famicom version (with a lockout chip of course). Perhaps it would have used a black shell. The user would be required to insert this Game Pak into his NES whenever he wanted to use a game on the Disk System. Otherwise the Disk Drive would be inert.
The second would have been the Disk Drive Unit, which would have had to attach to the expansion port underneath the NES. The user would have to snip the plastic cover off and press the Control Deck to the Disk Drive Unit firmly together. How the drive unit would have remained secure except for the friction connection is a matter of conjecture. I would think that the slots that held in the tabs of the expansion port cover may have been involved as well as the T-shaped groove cut into the bottom of the Control Deck. While I suppose it is feasible that Nintendo could have supplied long screws and instructed the user to replace the screws holding the Control Deck together with the longer screws, Nintendo was never enthusiastic about users opening its consoles.
Asthetically, I would imagine that the Disk Drive unit would have added several inches to the height of the NES Control Deck. The NES Control Deck has a trapezoidal shape with the lower half sloping inward, I would think that the Disk Drive Unit would be flush with the lower edge of the Control Deck. The resulting shape may have looked like a mushroom, not altogether an unfitting image for a Nintendo console. Otherwise, it may have resulted in a much more boxy look like the Gamecube. I also would think that the Disk Drive would be off-center and centered underneath the cartridge slot. Color-wise, I would suggest that the Disk Drive Unit would have been totally black or matched the gray on the lower part of the Control Deck with a black stripe of plastic on the right side.
The expansion port on the NES just does not have the signals necessary to implement the RAM adapter without a radical redesign. Additionally, it would look ugly for a thick cable to protrude from the top of a Game Pak to snake around the system to connect to the Disk Unit and keep the door from closing. The Famicom Disk System's RAM Adapter's cable uses 9 pins on the 12 pin connector to connect to the Disk Drive. That is where the 10 otherwise unused pins on the NES connector would have come into play. However, audio is also generated in the cartridge, and that requires a pin to send to the expansion port for mixing with the internal audio. Thus all 10 pins are used.
I would think that the NES could have powered itself and the Disk System using the NES-002 Power Adapter. The NES's AC Step Down Converter is rated for 9VAC, 1.3A output. The NES-001 Control Deck is rated for 9VDC, 850mA. That would leave about 450mA left to play with. The Famicom Disk System is rated for 9VDC, 400mA, so there should be sufficient milliamps for both a Control Deck and the Disk System to function without a need for an extra AC adapter or batteries. Also consider the Sharp Twin Famicom, which combines a Famicom and a Famicom Disk System and uses an Adapter providing 7.6VDC and 1.250A.
The Famicom Disk System's RAM Adapter had an expansion port covered with a shutter that was never used. It functions as a bidirectional 7-bit I/O port and is accessed by registers at $4026 & $4033. It was never used by any commercial product. I cannot fathom how Nintendo would have implemented this port given the cartridge door and push down design of the NES or if they even would have bothered. Perhaps they would have multiplexed these signals with the necessary RAM adapter signals on the cartridge connector and had the port on the Disk Drive Unit.
Physically, the disk system would have had to come in two pieces. The first would have been a RAM adapter, which would look like a typical NES Game Pak and function just like the Famicom version (with a lockout chip of course). Perhaps it would have used a black shell. The user would be required to insert this Game Pak into his NES whenever he wanted to use a game on the Disk System. Otherwise the Disk Drive would be inert.
The second would have been the Disk Drive Unit, which would have had to attach to the expansion port underneath the NES. The user would have to snip the plastic cover off and press the Control Deck to the Disk Drive Unit firmly together. How the drive unit would have remained secure except for the friction connection is a matter of conjecture. I would think that the slots that held in the tabs of the expansion port cover may have been involved as well as the T-shaped groove cut into the bottom of the Control Deck. While I suppose it is feasible that Nintendo could have supplied long screws and instructed the user to replace the screws holding the Control Deck together with the longer screws, Nintendo was never enthusiastic about users opening its consoles.
Asthetically, I would imagine that the Disk Drive unit would have added several inches to the height of the NES Control Deck. The NES Control Deck has a trapezoidal shape with the lower half sloping inward, I would think that the Disk Drive Unit would be flush with the lower edge of the Control Deck. The resulting shape may have looked like a mushroom, not altogether an unfitting image for a Nintendo console. Otherwise, it may have resulted in a much more boxy look like the Gamecube. I also would think that the Disk Drive would be off-center and centered underneath the cartridge slot. Color-wise, I would suggest that the Disk Drive Unit would have been totally black or matched the gray on the lower part of the Control Deck with a black stripe of plastic on the right side.
The expansion port on the NES just does not have the signals necessary to implement the RAM adapter without a radical redesign. Additionally, it would look ugly for a thick cable to protrude from the top of a Game Pak to snake around the system to connect to the Disk Unit and keep the door from closing. The Famicom Disk System's RAM Adapter's cable uses 9 pins on the 12 pin connector to connect to the Disk Drive. That is where the 10 otherwise unused pins on the NES connector would have come into play. However, audio is also generated in the cartridge, and that requires a pin to send to the expansion port for mixing with the internal audio. Thus all 10 pins are used.
I would think that the NES could have powered itself and the Disk System using the NES-002 Power Adapter. The NES's AC Step Down Converter is rated for 9VAC, 1.3A output. The NES-001 Control Deck is rated for 9VDC, 850mA. That would leave about 450mA left to play with. The Famicom Disk System is rated for 9VDC, 400mA, so there should be sufficient milliamps for both a Control Deck and the Disk System to function without a need for an extra AC adapter or batteries. Also consider the Sharp Twin Famicom, which combines a Famicom and a Famicom Disk System and uses an Adapter providing 7.6VDC and 1.250A.
The Famicom Disk System's RAM Adapter had an expansion port covered with a shutter that was never used. It functions as a bidirectional 7-bit I/O port and is accessed by registers at $4026 & $4033. It was never used by any commercial product. I cannot fathom how Nintendo would have implemented this port given the cartridge door and push down design of the NES or if they even would have bothered. Perhaps they would have multiplexed these signals with the necessary RAM adapter signals on the cartridge connector and had the port on the Disk Drive Unit.