19" Rack Mount
Because of 19 Inch Rack Mounts origin as mounting systems for railroad signaling relays, they are still sometimes called relay racks, but the 19 inch rack format has remained a constant while the technology that is mounted within it has changed to completely different fields. This standard rack mount arrangement is widely used throughout the telecommunication, computing, audio, entertainment and other industries, though the Western Electric 23-inch standard, with holes on 1-inch centers, prevails in telecommunications.

19 inch rack mounts are most often used to house professional audio and video equipment, including amplifiers, effects units, interfaces, headphone amplifiers, and even small scale audio mixers. They are also widely used for computer server equipment, allowing for dense hardware configurations without occupying excessive floor space or requiring shelving. A third common use for rack-mounted equipment is industrial power, control, and automation hardware, typically in 46U racks.