BIOS Files, Copyright, and the Law: The Real Rules Behind Emulation
Emulator software and the copyrighted files it needs to run are two separate legal questions with two separate answers — and conflating them is where most confusion about 'is emulation legal' comes from.
“Is emulation legal?” is really two separate questions wearing one trench coat: is writing and distributing emulator software legal, and is obtaining and using the copyrighted files (BIOS images, game ROMs) that software needs to actually run something legal. The two questions have different, independently-settled answers, and most confusion about emulation’s legal status comes from conflating them.
Writing an emulator: settled by Sony v. Connectix
Sony Computer Entertainment, Inc. v. Connectix Corp., decided by the Ninth Circuit Court of Appeals in 2000, is the case most directly on point. Connectix built Virtual Game Station, a PlayStation emulator, which required repeatedly copying Sony’s copyrighted PlayStation BIOS during reverse engineering — the process of studying how the original hardware worked in order to reproduce its behavior independently, without copying Sony’s actual code into the finished product. The Ninth Circuit ruled that this intermediate copying, done for the purpose of understanding an interface well enough to build independent, interoperable software, was protected as fair use — reversing a lower court’s injunction against Connectix. The court also rejected Sony’s trademark tarnishment claim over the product. The ruling didn’t hinge on emulation being some special exception; it applied established fair-use reasoning about reverse engineering for interoperability to this specific case, with the emulator itself containing none of Sony’s copyrighted material in its final, shipped form.
That ruling does not cover ROM or BIOS distribution
This is the part that gets lost in casual summaries: Sony v. Connectix is about the legality of building an emulator through reverse engineering — it says nothing about the separate act of copying and distributing an actual copyrighted BIOS image or game ROM file to someone else. Distributing a copyrighted work you don’t own the rights to remains ordinary copyright infringement, entirely untouched by this precedent, regardless of whether the recipient intends to use it with an emulator. The clearest illustration of the practical consequences here is Nintendo’s 2018 lawsuit against the operators of the ROM sites LoveROMS and LoveRETRO, which Nintendo described as “built almost entirely” on unauthorized distribution of its copyrighted games — the sites went offline immediately after the complaint, and the operators ultimately agreed to a $12,230,000 judgment along with a permanent injunction and surrendering the domains to Nintendo. Nothing about that case involved the legality of emulator software; it was squarely about unauthorized distribution of copyrighted game files.
A narrow, specific exemption for institutional preservation
Separately, the U.S. Library of Congress’s triennial DMCA rulemaking has recognized a narrow exemption relevant to preservation specifically: as of the exemption finalized on October 26, 2018, eligible libraries, archives, and museums may circumvent access controls to preserve video games that are no longer supported (for example, games that depended on a since-shuttered authentication server), strictly for preservation purposes. That exemption comes with real limits — no commercial purpose, and the preserved game may only be made available on the physical premises of the qualifying institution, not distributed publicly — so it addresses a specific institutional preservation scenario, not general public distribution or use.
The practical rule this adds up to
Building or using emulator software to run games you legitimately own is on solid legal ground, resting on the same reverse-engineering-for-interoperability reasoning Sony v. Connectix established. Obtaining copyrighted BIOS files or ROMs you have no rights to — even to use with a perfectly legal emulator — is a separate act that ordinary copyright law still governs, and the emulator’s own legality doesn’t extend to cover it. Dumping a cartridge or disc you personally own, as covered in ROM dumping and preservation, is the practical way this distinction plays out for an individual: the software is legal, and the file is legitimately yours because you created it yourself from hardware you own — a materially different situation from downloading someone else’s copy of the same file.
Sources: Sony Computer Entertainment, Inc. v. Connectix Corp. — Wikipedia, Sony Computer Entertainment, Inc. v. Connectix Corp., 203 F.3d 596 (9th Cir. 2000) — Justia, U.S. Copyright Office fair use summary — Sony v. Connectix, Nintendo Wins $12.2 Million in Lawsuit Against ROM Site Owners — Variety, The Expanded DMCA Exemption for Video Game Preservation — Electronic Frontier Foundation