Right. To be clear, when I mentioned the idea for a USB CD-ROM interface I was speaking merely from the perspective of a PC-Engine Core + IFU-30 + CD-ROM setup. The reason being, PCE-Core and IFU units are very easy to find in a working state. CD-ROM units are not. This also means that if one were to produce an adapter, it would be a simpler job since the CD-ROM unit is bare-bones. Another pro to using this setup as a base is that PCE-Core and IFU-30 components are modular. So you can swap them in and out as needed when one goes bad.
I'm not so sure that replacing the CD-ROM unit alone would be any easier than replacing the whole IFU+CDROM combination.
One reason is the connector - this is much more difficult to find than something which could fit on the back of a white PC-Engine. The other main reason is the lack of technical information on the interface to the CDROM unit.
I understand that the overall interface to CDROM is basically SCSI... Back in 1989 or so, I also saw an NEC CDROM interface to a PC, which used a SCSI card and had a different interface unit (but the same CDROM drive as the PC Engine).... but who says that the SCSI brains are in the CDROM unit, and not the interface unit (leaving a lower-level interface between IFU and CDROM) ?
I could much more easily see somebody coming up with an FPGA implementation of IFU+CDROM on a SDCard, than simply CDROM replacement. I could also see this being something which wouldn't necessarily be restricted to PC Engine backplanes, but also as a modification to Duo machines.
-Dave
