19-inch rack
A 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules. Each module has a front panel that is 19 inches (482.6 mm) wide. The 19-inch dimension includes the edges or ears that protrude on each side which allow the module to be fastened to the rack frame with screws.
Overview and history
Equipment 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 mountable, or occasionally simply shelf. The height of the electronic modules is also standardized as multiples of 1.752 inches (44.50 mm) or one rack unit or U (less commonly RU). The industry standard rack cabinet is 42U tall.
The term relay rack appeared first in the world of telephony. By 1911, the term was also being used in railroad signaling. There is little evidence that the dimensions of these early racks were standardized. The 19-inch rack format with rack-units of 1.75 inches and holes tapped for 12-24 screws with alternating spacings of 1.25 inches and 0.5 inch was an established standard by 1934. The EIA standard was revised again in 1992 to comply with the 1988 public law 100-418, setting the standard U as 44.5 mm (15.9 mm + 15.9 mm + 12.7 mm), making each "U" officially 1.752 inches.
