When were four track reel to recorders available?

Four-track reel-to-reel recorders first appeared in the 1950s. Ampex released the Model 350 in 1956, which was the first commercially available four-track recorder. It was soon followed by other models from companies such as Scully, Magnecord, and Presto. Four-track recorders quickly became popular for recording music and sound effects, as they offered a higher degree of fidelity and flexibility than mono or two-track recorders.