This teeny-tiny article needs some work. You can help us by expanding it.
The CD-ROM² (シーディーロムロム, officially pronounced "CD-ROM-ROM") is an add-on for the PC Engine allowing the console to run games from CD-ROMs. It was originally released in Japan in December 1988, with its Western equivalent being the TurboGrafx-CD.
Unlike most of its competitors, particularly the Sega Mega-CD (from 1991) and the likes of the Neo Geo CD (1994) or Atari Jaguar CD (1995), the CD-ROM² is by default, a regular a CD-ROM player. Plugged into the mains and a pair of speakers or headphones, the CD-ROM² functions as an entirely separate device and theoretically does not need to be concerned with video games at all (which is not dissimilar to earlier home computers reliant on compact cassettes).
For the CD-ROM² to become a PC Engine accessory, it requires an Interface Unit (originally sold separately, later bundled with the CD-ROM²), which makes use of a special expansion port on the back of the device to communicate with the PC Engine console. Playing games, however, requires the use of a System Card, which will provide the combined unit with instructions on how to interact with itself, and allow it access to more ROM and RAM.
CD-ROM² units are were also an option for the PC-8801 MC. The units which shipped with PC-8801 MCs are identical to their PC Engine counterparts, albeit with the "²" removed.
As time moved on, there became less of a need for a stand-alone CD-ROM². The Super CD-ROM² offers more functionality and products such as the PC Engine Duo or LaserActive have the data found on system cards built-in.
|CD-ROM² (1988) | Super CD-ROM² (1991) | Arcade CD-ROM² (1994)|
|CD-ROM² (Interface Unit | ROM² Adaptor) (1988) | TurboGrafx-CD (1989) | PC Engine Duo (1991) | Super CD-ROM² (Super ROM² Adaptor) (1991) | TurboDuo (1992) | PC Engine Duo-R (1993) | LaserActive (1993)|
|System Card | Super System Card | Arcade Card Pro | Arcade Card Duo|