From an Internet Archive Blog Post:
Our online digital library is best known for its immense archive of web pages and websites in the Wayback Machines. Less well known are the million-plus recordings the site has stored digitally and made available to the general public, mostly from 78s, albums and CDs.
Highlighting the growing importance of music on archive.org is the debut this month of our new music player. While you can listen to only a sample of most modern songs, the new player now embeds Spotify and YouTube versions of the full song, so listeners are now able to click right from archive.org to those services and listen to the full track.
We’ve digitized at high resolution the album liner notes, including full CD booklets and the paper labels on the discs themselves. And at the bottom of each page are lists of related music tracks – covers, other versions of the same song done by the same artist and compilations where that song has been used.