C64 and NES are based on the 6502 processor, the Amstrad and ZX spectrum are based on the z80 processor, the Amiga is based on the 68000 processor. All three of

C64 and NES are based on the 6502 processor, the Amstrad and ZX spectrum are based on the z80 processor, the Amiga is based on the 68000 processor. All three of those processors have publicly available instruction set architectures [1][2][3]. IANAL, implementing the instruction sets and reverse engineering the firmware on those systems would be protected under fair use under copyright law [4]. You can be sued in civil court for copyright infringement, but you would have a valid legal defense that is supported by precedent in that case. You however could be sued if the hardware was protected by patents, but in the case of older hardware like you mentioned, patents would have been past the 20 year expiration for patent protection. You could be sued under trade secret, but the prosecution would have to show that you violated a non-disclosure agreement with them. If you never signed one, and reverse engineered the system, it would be an invalid case. The most likely explanation for why you cannot find commercial emulators is because open source ones exist. What incentive does a software developer have to compete with a free product? [1] https://masswerk.at/6502/6502_instruction_set.html https://masswerk.at/6502/6502_instruction_set.html [2] http://z80.info/z80oplist.txt http://z80.info/z80oplist.txt [3] http://wpage.unina.it/rcanonic/didattica/ce1/docs/68000.pdf http://wpage.unina.it/rcanonic/didattica/ce1/docs/68000.pdf [4] https://ngminusone.wordpress.com/2018/07/10/are-emulators-legal-a-look-at-the-legal-grey-area-of-video-game-emulation/ https://ngminusone.wordpress.com/2018/07/10/are-emulators-le...