16 and 20" discs — Although 12" was the largest disc diameter used in consumer products, broadcasting studios made use of 16" and 20"-diameter 78 rpm acetate "transcriptions," used for time-delaying programs and for prerecording broadcasts. These could provide up to 20 minutes of unbroken program material with very good fidelity (indistinguishable from live to casual, but not to critical listeners). Early classical LP recordings were in fact initially recorded on 20" 78-rpm acetates for later transfer to LP. 16" turntables are still seen in professional broadcast equipment, although it is probably very rare that any disk larger than 12" is ever played on them. Quote taken from Wikipedia, the free encyclopedia.