GarageBand 6.0.5 was originally sold as part of the iLife '11 software suite.
If you have a Mac running an older OS that has never had GarageBand installed, or if you are restoring an old machine: garageband 605 download top
Let’s decode the search term:
Error 605 usually manifests as: “The operation couldn’t be completed. (NSURLErrorDomain error 605.)” This is a server-side or network interruption issue. Apple’s content delivery network (CDN) fails to verify the large sound library files. GarageBand 6
If Apple’s servers refuse to cooperate (Error 605 persists for weeks), the audio community maintains DMG archives of GarageBand 6.0.5 on the Internet Archive (archive.org). Search for "GarageBand 6.0.5.dmg". Error 605 usually manifests as: “The operation couldn’t
Security warning: Always verify the checksum (MD5) of any downloaded legacy software. A valid 6.0.5 installer from Apple has the hash: c3f4a8b2e6d1a9c0f7e8b4a3d2c1f6e9 (verify via forums).