开发进行时...

U是一种表示服务器外部尺寸的单位，是unit的缩略语，详细的尺寸由作为业界团体的美国电子工业协会（EIA）所决定。

之所以要规定服务器的尺寸，是为了使服务器保持适当的尺寸以便放在铁质或铝质的机架上。机架上有固定服务器的螺孔，以便它能与服务器的螺孔对上号，再用螺丝加以固定好，以方便安装每一部服务器所需要的空间。

规定的尺寸是服务器的宽（48.26cm＝19英寸）与高（4.445cm的倍数）。由于宽为19英寸，所以有时也将满足这一规定的机架称为“19英寸机架”。厚度以4.445cm为基本单位。1U就是4.445cm，2U则是1U的2倍为8.89cm。

所谓“1U的PC服务器”，就是外形满足EIA规格、厚度为4.445cm的产品。设计为能放置到19英寸机柜的产品一般被称为机架服务器。

服务商按这个单位收钱.越大费用越多.

A typical section of rail server rack, showing rack unit distribution.

A rack unit is a unit of measure used to describe the height of a server, network switch or other similar device mounted in a 19-inch rack or a 23-inch rack (refers to width of rack). One rack unit is 44.45 mm (1.75 in ) high. One rack unit is 44.45 mm (1.75 in) high.

One rack unit is commonly designated as "1U"; similarly, 2 rack units are "2U" and so on. One rack unit is commonly designated as "1U"; similarly, 2 rack units are "2U" and so on. The size of a piece of rack mounted equipment is usually described as a number in "U". The size of a piece of rack-mounted equipment is usually described as a number in "U". One rack unit is also sometimes referred to as "1RU"; most racks have 42 U of height. One rack unit is also sometimes referred to as "1RU"; most racks have 42 U of height.

Professional audio and video gear often comes with rack mount options and use the same measurement specifications. Professional audio and video gear often comes with rack mount options and use the same measurement specifications.

Half-rack units typically describe units that fit in a certain number of rack units, but occupy only half the width of the rack (9.5 inches or 241 mm). Half-rack units typically describes units that fit in a certain number of rack units, but occupy only half the width of the rack (9.5 inches or 241 mm). For example, a "4U half-rack" DVCAM deck would occupy 4U (4 × 1.75 inches) height × 9.5 inches width. For example, a "half-4U rack DVCAM deck would occupy 4U (4 × 1.75 inches) height x 9.5 inches width. In theory, two half-rack decks could occupy the 4U space. In theory, two half-rack decks could occupy the space 4U.

A front panel or filler panel in a rack is not an exact multiple of 1.75-inches (44.45 mm). A front panel or filler panel in a rack is not an exact multiple of 1.75-inches (44.45 mm). To allow space between adjacent rack mounted components, a panel is 1 ⁄ 32 inch (0.031 inch or 0.79 mm) less in height than the full number of rack units would imply. To allow space between adjacent rack mounted components, a panel is 1 / 32 inch (0,031 inch or 0.79 mm) in height less than the full number of rack units would imply. Thus, a 1U front panel would be 1.719 inches (43.66 mm) high. Thus, a 1U front panel would be 1,719 inches (43.66 mm) high. If n is number of rack units, the formula for panel height is h = (1.750n 1.750n − 0.031) inch = (44.45n 44.45n − 0.79) mm. If n is number of rack units, the formula for panel height is h = (1.750n 1.750n - 0,031) = inch (44.45n 44.45n - 0.79) mm.

Coincidentally, a rack unit is equal to a vershok , which is an obsolete Russian length unit. Coincidentally, a rack unit is equal to a vershok, which is an obsolete Russian length unit.