The FC Twin has separate circuitry and cartridge slots for the NES and SNES. With the Super Game Boy adaptor, Nintendo Game Boy cartridges can also be used. It features a single-pole, double-throw power switch with open position; the switch can be thrown to 8-Bit (NES) or 16-Bit (SNES), or set to off.
The FC Twin console uses SNES compatible controllers and devices such as the Super Scope and Konami Justifier light guns, but cannot use NES compatible controllers and devices such as the NES Zapper peripheral for Duck Hunt. The Super Nintendo controller buttons otherwise map to the NES controller inputs (B maps to Y, A maps to B. A maps to turbo B, X maps to turbo A; L and R serve no function). When using any controllers besides the actual FC Twin ones, the A and X buttons do nothing during 1-player or 2-player NES play. Gauntlet II pauses when L or R is hit.
The FC Twin connects through an RCA connector, and can be hooked into a surround sound system. When using stereo and surround output from these systems, NES sounds and music may seem very different from their typical mono output. Using output modes that properly generate mono sound, either through a single center speaker or cloned to multiple speakers, the sound output sounds mostly identical to the original NES. The FC Twin does not produce some sounds faithfully, even with mono output; sound effects in the Super Mario Bros. series games will for example immediately seem different. Nevertheless, some later models of the console produce NES sound much more faithfully than units made closer to launch. Recent models produce sound with complete fidelity.
FC Twin with two games in itThe FC Twin uses a card slot reader rather than a ZIF connector. The second-generation NES also used a card slot reader, and featured no 10NES lock-out chip; however, unlike the top-loading NES 2, the FC Twin is completely compatible with the Galoob Game Genie without the use of an adaptor. Both the official NES 2 and the FC Twin capitalize on the card slot reader's greater reliability; games rarely suffer from bad connections as they did with the original ZIF socket. In the FC Twin, the NES cartridge still has to be reseated occasionally. The pins can misalign and short across each other or otherwise fail to connect properly, requiring users to maneuver the game cartridge until it works.
As tested by consumers, the following NES games are not compatible with the FC Twin
- After Burner
- Athletic World (cannot use Power Pad)
- Bandit Kings of Ancient China
- 'Captain Planet and the Planeteers'
- '''Castlevania III: Dracula's Curse'''
- '''Cheetahmen II'''