Archival sound recordings at the BBC are held within the Information & Archives department which manages the central radio, television, music, image, written archives and the heritage collection of artworks and artefacts.The BBC began making sound recordings in 1931 for production and broadcasting purposes. Most broadcasts were live and never recorded, but a process for selecting and cataloguing some recordings developed from the late 1930s. All national ('network') radio has been captured and held since November 2008. Other categories of recordings include selected unedited material, sound effects and accent, dialect and traditional folk music of the British Isles. There are more than 350,000 hours of radio and other audio recordings on most physical legacy formats (coarse groove and vinyl discs; 1/4" analogue tape; audiocassettes, etc). Extensive preservation and digitisation programmes have transferred approximately 40% of sound recordings to .wav and .bwav files. Supporting recorded sounds, the Written Archives Centre at Caversham, Berkshire provides academic and professional researcher access to the BBC's historic business papers and production documents and hold essential primary sources on the history of BBC radio.