Not all MAME versions are created equal. Version 0.139u1 (released around 2011) represents a unique inflection point:
Key takeaway: If you own an Android device (especially Retroid Pocket, Anbernic, or even an old phone), MAME4droid 0.139u1 will give you the largest library of working games relative to hardware resources. mame4droid 0.139u1 roms archive.org
Here is the nuanced reality:
Ethical best practice: Use Archive.org’s MAME 0.139u1 ROMs as a preservation tool. If you love a game, support modern re-releases (e.g., Arcade1Up, Hamster’s Arcade Archives, Capcom Arcade Stadium). Not all MAME versions are created equal
The Internet Archive operates as a digital library. While many ROMs on Archive.org are abandonware or in legal gray areas, copyright law is clear: downloading full commercial ROM sets for games you do not own is copyright infringement in most jurisdictions. Key takeaway: If you own an Android device
A useful approach: Use the 0.139u1 set as a research and preservation tool. If you own the original arcade PCB, you have a legal right to a backup ROM. For most hobbyists, the ethical middle ground is to download only games that are: