|SANYO DENKI --- 1U Rack Server
A rack server, also referred to as a rack-mount server, is the standard size server used for mounting inside a datacenter server cabinet or rack frame infrastructure. The EIA (Electronic Industries Alliance) standard server rack has a width of 19 inches (482.6 mm). One rack unit is 1.75 inches (44.5 mm) high.
The size of a piece of rack-mounted equipment is frequently described by a number and "U". For example, one rack unit is often referred to as "1U", two rack units as "2U" and so on. A typical full size rack is 42U, which means it can hold just over six feet (1.8 m) of closely stacked equipment.