PAL PC-ENGINE, modding to make multi regional???

[Papercut]

System Card 1.0
System Card 2.0 (Super System) - more memory, plays Super CD games
System Card 2.1 (Super System) - adds Karaoke
System Card 3.0 (Arcade Pro) - more memory, plays Arcade CD games

something like that, anyway.

The Arcade Duo is a version of the Arcade Pro with less memory aimed at Duo versions of the PC Engine (those with built in CD drives), which already have the extra memory of the Super System card (v2.x) built in.

[MD]

System Cards (ignoring American one...)

V1.0 - CD-ROM2 Card, 128K (1 Megabit) (Note: Altered Beast will only work with this card.)

V2.0 - CD-ROM2, 256K (2 Megabits), most games would use the extra memory and would load faster.

V2.1 - CD-ROM2, 256K (2 Megabits), add CD+G abilities.

V3.0 - Super CD-ROM2, 512K (4 Megabits). Allowed Super CD-ROM games to work. Although a lot of Super CD-ROM games would work on a V2.1 card but would take longer to load. Was built in on the Super CD-ROM system and Duos.

Arcade Card Pro - Super CD-ROM2, 2 Megabytes (16 Megabits). Had no extra hardware, just had a lot more ram and a V3.0 BIOS. Allowed Arcade CD-ROM games to use the extra memory to store sprites, CG animations, etc. Required for the PC Engine CD-ROM system (although does work on the Duo...).

Arcade Card Duo - As Arcade Card Pro but without the BIOS, so works on Duo and Super CD-ROM2 systems.

Games Express CD Card - Games Express who made adult hentai games made their own CD-ROMs and made a BIOS card and RAM card to run the few CD-ROM games they did make. It's unofficial and won't run PC Engine CD-ROM2 or Super CD-ROM2 games (the Games Express games won't work on any System Card).