Reel-to-reel systems use tape that is 1⁄4” (6.35 mm), 1⁄2", 1", or 2" in width and normally moves at 7.5 or 3.75 inches (19 or 9.5 cm) per second. This compares to 0.15 inches (3.81 mm) wide and 1.875 inches (4.75 cm) per second for a cassette (although some open reel machines support other speeds as per section below). By writing out the same audio signal across more tape, reel-to-reel systems offer much higher fidelity, at the cost of much larger tapes. In spite of the larger tapes, less convenient use and generally higher cost media, reel-to-reel systems remained popular in audiophile settings into the 1980s.
Reel-to-reel tape was also used in early tape drives for data storage on mainframe computers, video tape recorder (VTR) machines, and high quality analog audio recorders, which have been in use from the early 1940s, up until the present. Studer, Stellavox and Denon still produced reel to reel tape recorders in the 1990s, but as of 2017, only Mechlabor continues to manufacture analog reel-to-reel recorders.
The reel-to-reel format was used in the earliest tape recorders, including the pioneering German-British Blattnerphone (1928) machines of the late 1920s which used steel tape, and the German Magnetophon machines of the 1930s. Originally, this format had no name, since all forms of magnetic tape recorders used it. The name arose only with the need to distinguish it from the several kinds of tape cartridges or cassettes such as the endless loop cartridge developed for radio station commercials and spot announcements in 1954, the full size cassette, developed by RCA in 1958 for home use, as well as the compact cassette developed by Philips in 1962, originally for dictation.
The earliest machines produced distortion during the recording process which German engineers significantly reduced during the Nazi Germany era by applying a "bias" signal to the tape. In 1939 one machine was found to make consistently better recordings than other ostensibly identical models, and when it was taken apart a minor flaw was noticed. It was introducing an AC signal to the tape, and this was quickly adapted to new models using a high-frequency AC bias that has remained a part of audio tape recording to this day. The quality was so greatly improved that recordings surpassed the quality of most radio transmitters, and such recordings were used by Adolf Hitler to make broadcasts that appeared to be live while he was safely away in another city.
American audio engineer Jack Mullin was a member of the U.S. Army Signal Corps during World War II. His unit was assigned to investigate German radio and electronics activities, and in the course of his duties, a British Army counterpart mentioned the Magnetophons being used by the allied radio station in Bad Nauheim near Frankfurt. He acquired two Magnetophon recorders and 50 reels of I.G. Farben recording tape and shipped them home. Over the next two years, he worked to develop the machines for commercial use, hoping to interest the Hollywood film studios in using magnetic tape for movie soundtrack recording.