 Each volume was issued on either compact disc, cassette or (with volumes issued prior to 1991) vinyl record.Individual volumes generally contained anywhere between 18 and 22 tracks, and represented the highlighted time period's most popular and noteworthy tracks.Also included was a booklet, containing liner notes written by some of the most respected historians of the genre, photographs of the artists, and information on the songs (writers, performers and peak position on "Billboard magazine"'s Billboard Hot 100 chart).