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In December 1988 NEC began to release video games on CD-ROM for its PC Engine console. These CD-ROM² systems, beginning with the appropriately titled CD-ROM² would take a number of forms over the coming years, complementing the base system and its range of games on HuCard.
The complex nature of the CD-ROM² line has led to NEC Retro grouping all CD-based PC Engine variants under the same umbrella term. In reality there are three CD-ROM² formats; "CD-ROM²" (シーディーロムロム), "Super CD-ROM²" (スーパーシーディーロムロム) and "Arcade CD-ROM²" (アーケードシーディーロムロム). Theoretically all CD-ROM² systems can run software of all three formats, however some require "system cards" to enable this functionality.
Unlike HuCards, PC Engine CD-ROMs are not region locked, and therefore will function on their TurboGrafx-16 equivalent units and vice versa. The system cards however, are region locked, and so may require extra adapters to function.
Despite the stylising of the name, "CD-ROM²" is officially pronounced "CD-ROM ROM", as opposed to "CD-ROM squared" or "CD-ROM two".
The original CD-ROM² standard debuted alongside the CD-ROM² hardware in December 1988. All CD-ROM² systems can run CD-ROM² games natively.
In North America this format was simply marketed as games for the TurboGrafx-CD (or occasionally "Turbo CD games"), as at the time only one format existed. However, after the release of the Turbo Duo, TTI reverted to the "CD-ROM² System" branding used in Japan.
The Super CD-ROM² debuted in December 1991 (with the Super CD-ROM² unit), and quickly became the de facto standard for CD-based PC Engine games moving forward. Initially all PC Engine hardware required the Super System Card to access the Super CD-ROM² library - the contents of the card were later built into the PC Engine Duo and its derivatives.
This format also made it to North America, however a change in distributors and the low key nature of the TurboGrafx-16 library made the situation less clear cut. While the Super System Card was still an option for TurboGrafx-16 users, games were often simply marketed as "DuoSoft" or "Duo CDs", i.e. built specifically for that console, rather than a TurboGrafx-16 + TurboGrafx-CD combo. Standard CD-ROM² games released in North America after the Turbo Duo were also labeled as such to try and alleviate some confusion.
A third format, the Arcade CD-ROM² debuted in March 1994, towards the end of the PC Engine's life. Unlike the Super CD-ROM² format, Arcade CD-ROM² technology was never built into hardware, so always requires the use of an Arcade Card Pro (for older hardware) or Arcade Card Duo (for systems with Super CD-ROM² support built-in (typically a PC Engine Duo, hence its name)).
Arcade CD-ROM² games were only officially released in Japan, although with the correct setup, will also function on North American systems.
In addition, several Super CD-ROM² games can be enhanced by the Arcade card, but will work fine with Super CD-ROM²-compatible hardware:
Some titles built to the Super CD-ROM² standard, particularly unlicensed games, require the use of the HuCard slot in order to bypass security features(?). As no PC Engine derivative contains more than one slot, this effectively writes off the use of a Super System Card, and therefore makes these games incompatible with older PC Engine hardware. Systems such as the PC Engine Duo and TurboDuo have Super CD-ROM² support built-in without the need for system cards, meaning a small number of titles are only compatible with these Duo systems.
The LD-ROM² format is a similar format to the above but is this time distributed on LaserDisc, specifically for use with the LaserActive by Pioneer using the NEC PAC (PAC-N10/PAC-N1) add-on.
Only a small handful of games were released in this format; fewer than the other format supported by the LaserActive, Mega LD, which does a similar thing with the Sega Mega Drive.
The PC Engine and TurboGrafx-16 on their own have no means of saving game data, meaning every game written for the platform prior to late 1988 had to rely on password saves (or ditch any form of saving altogether). With the CD-ROM², that changed - every unit has 2kB of built in memory (recognised as 2,000 blocks) which can be accessed by software both on CD-ROM or HuCard.
However, like many of NEC's memory solutions, the system is not ideal, as save data is kept alive by a supercapacitor, rather than a traditional battery back-up or solid state saving system. The supercapacitors in use in CD-ROM² hardware can retain their charge for a couple of weeks if the PC Engine is not turned on, after which all save data will be erased. NEC used this supercapacitor solution in all of their CD-ROM² systems, up to and including the PC Engine Duo-RX in 1994.
Two options exist for longer-term saving, both introduced some years after the CD-ROM²; the Ten no Koe Bank and Memory Base 128. Other options exist for HuCard games, but their use of the rear expansion port means a CD-ROM² system cannot be plugged in simultaneously.
|CD-ROM² (1988) | Super CD-ROM² (1991) | Arcade CD-ROM² (1994)|
|CD-ROM² (Interface Unit | RAU-30) (1988) | TurboGrafx-CD (1989) | PC Engine Duo (1991) | Super CD-ROM² (Super CD-ROM² Adaptor) (1991) | TurboDuo (1992) | PC Engine Duo-R (1993) | LaserActive (1993)|
|System Card | Super System Card | Arcade Card Pro | Arcade Card Duo|