 The 100 Series released mainly instrumental jazz LPs and the 400 Series featured vocalists.The album catalog numbers were often denoted by the prefix "LP" on the album cover and "ALS" or "ALR" on the record label.Atlantic commenced releasing 12 inch LP records with the establishment of their 1200 Series in 1949 with an album consisting of three 78 RPM records of Walter Benton's poetry.