The history of General Computer Corporation's[0] arcade enhancement boards is an interesting example of this kind of "derivative" work. GCC made an enhancement

The history of General Computer Corporation's[0] arcade enhancement boards is an interesting example of this kind of "derivative" work. GCC made an enhancement board for Missile Command and later for Pac Man ("Crazy Otto", which became "Ms. Pac Man"). Rather than employing simple "ROM hacks" as other enhancement board manufacturers did, GCC specifically built their enhancement hardware not to contain any code copied from the original game ROM. Their hardware patched the existing ROM only by overlaying their code onto the original ROMs, not by copying any of the original code[1]. There's some neat detail in the background slides here[2]. I'd love to hear that talk but I'm not immediately a recording of it. [0] https://en.wikipedia.org/wiki/General_Computer_Corporation https://en.wikipedia.org/wiki/General_Computer_Corporation [1] https://web.stanford.edu/class/sts145/Notes/3_game_business/html/legal_issues_notes.htm https://web.stanford.edu/class/sts145/Notes/3_game_business/... [2] https://trilobyte.com/pdf/golson_ReplayFX_2015.pdf https://trilobyte.com/pdf/golson_ReplayFX_2015.pdf