An album is a recording originally issued in gramophone format, followed by the vinyl format, and has then been issued in other formats such as compact cassette, compact disc, and increasingly in digital formats such as mp3, aac, alac, or flac. audio albums in physical form are often provided with decorative covers (cover art) and liner notes and inserts about the music and recording, giving background information and analysis of the recording, lyrics and librettos, images of the performers, and other images and text, as well as thanking contributors. when supplied with compact discs they are known as cd booklets. historically, the term "album" was applied to a collection of various items housed in a "book" format, and in musical usage the word was used for collections of short pieces of printed music from the early nineteenth century. later, collections of related 78rpm records were bundled in book-like albums (one side of a 78 rpm record could hold only about 3.5 minutes of sound). when long-playing records were introduced, a collection of pieces on a single record was called an album; the word was extended to other recording media such as compact disc, minidisc, compact audio cassette, and digital or mp3 albums, as they were introduced. the introduction of cds to radio caused a bit of a crisis for a generation of djs, who didn't know whether an album of music on a cd should still be called an album, as they had all grown up with 33-rpm lps, which they considered synonymous with albums.