Built into a cabinet that has a standard width of 19" or 24". All types of electronics and computing devices come in rack-mounted packages, including servers, test instruments, telecommunications components, tape drives and audio and video equipment. The units are bolted to the side frames. If equipment is not rack mountable, it can be placed on shelves. The height of a rack-mounted device is specified in a unit (U) measure or rack unit (RU). 1U (or 1RU) is 1.75" from top to bottom. See blade server
Rack Mount Cabinet
This is a sales brochure picture showing the variety of shelves available for 19" rack mount cabinets. Side and rear panels, doors, locks, fans and a host of other accessories are also offered. (Image courtesy of AMCO Engineering Company.)
One, Two and Three Rack Units
Each rack unit (U) is 1.75" thick from top to bottom.
A Rack of Betacams
In datacenters and professional studios around the world, equipment is routinely rack mounted. These Betacam videotape recorders are in a TV studio with rooms full of equipment. Each Betacam recorder takes 5U of vertical rack space.