A master reel is a single-track mono or two-track stereo reel-to-reel which stores the master recording of a professional record album. These tapes are archived in a cold room or a very cold safe. A backup copy of a master reel, known as a safety copy, is always made to ensure the recording will survive a failure of the master reel. Most modern studios use CDs or hard drives as their master format. The format of a master reel is outdated for most modern recording studios.