While they don't host the files themselves, they provide the "checksums" (digital fingerprints) so you can verify that an ISO you found in an index is a 100% accurate, uncorrupted copy. Conclusion

In many jurisdictions, downloading an ISO of a game you do not physically own is considered copyright infringement. Conversely, creating a digital backup (ripping an ISO) from a physical retail disc that you legally bought and own generally falls under or personal backup provisions. The Role of Digital Preservation

Because physical media degrades over time—a phenomenon known as "disc rot"—centralized, non-profit institutions have taken over the bulk of safe game archiving. 1. The Internet Archive (Archive.org)

An (or disc image) is a single file that contains an exact sector-by-sector copy of an entire optical disc.