![]() in all cases to be a whole multiple of 1 3⁄ 4 inches". The height of the different panels will vary, . ![]() But in light of the rapid growth of the toll network, the engineering department of AT&T undertook a systematic redesign, resulting in a family of modular factory-assembled panels all "designed to mount on vertical supports spaced 19 1⁄ 2 inches between centers. Once serial production started, they were built into custom-made racks, one per repeater. The earliest repeaters from 1914 were installed in ad hoc fashion on shelves, in wooden boxes and cabinets. The 19-inch rack format with rack-units of 1.75 inches (44.45 mm) was established as a standard by AT&T around 1922 in order to reduce the space required for repeater and termination equipment in a telephone company central office. There is little evidence that the dimensions of these early racks were standardized. īy 1911, the term was also being used in railroad signaling. The term relay rack appeared first in the world of telephony. The industry-standard rack cabinet is 42U tall however, 45U racks are also common. ![]() The height of the electronic modules is also standardized as multiples of 1.75 inches (44.45 mm) or one rack unit or U (less commonly RU). ![]() Common uses include computer servers, telecommunications equipment and networking hardware, audiovisual production gear, music production equipment, and scientific equipment.Įquipment designed to be placed in a rack is typically described as rack-mount, rack-mount instrument, a rack-mounted system, a rack-mount chassis, subrack, rack cabinet, rack-mountable, or occasionally simply shelf. The 19 inch dimension includes the edges or ears that protrude from each side of the equipment, allowing the module to be fastened to the rack frame with screws or bolts. Each module has a front panel that is 19 inches (482.6 mm) wide. A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. ![]()
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