The thread-starter asked me to chime in, here we go:
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Since I realize we have a lot of newer members who haven't heard previous discussions on the legality of "teh ROMs", here you go:
(1) Unless the copyright owner of the game has explicitly released the rights to the game (very, very rare), downloaded ROMs are by-and-large illegal. As you will see in the next few points, when talking about video games on forums like these, that almost always means illegal.
(2) that "back-up" copy exception is read so narrowly that about the only people that get away with it are entites like libraries trying to protect their collection
(3) "Abandonware" without written intent is a myth. You have to explicitly release the copyright, and be in a position to do so.
(4) The legal reason behind keeping copyrights in place is that the owner has the monoply of rights to exploit the work: in the early years or ROM-whoring, the whores blathered on that they were never going to use them again. Then all the arcade collections, games-in-a-joystick, paid-online legal ROM services, XBox arcade and Wii arcade started coming out.
(5) Any, let me repeat, any use of copyright-protected material to make a new (what we call "derivative") work makes the new work illegal.
(6) is it possible to make a new program/device/system that works completely independently of the copyrighted material, but that interacts with it? Yes: that was the lawsuit over the original Game Genie . Galoob won. Still, it's very difficult to do and Galoob spent a lot of engineering R&D dollars and still had to go through years of litigation to prove their case. Most individuals cannot afford that.
I'm sure I forgot something, but that should help for now.