How large is the server 1U size?

U is a unit representing the external dimensions of the server and is an abbreviation of unit. The detailed size is determined by the American Electronic Industry Association (EIA) as an industry group.

The reason for specifying the server size is to keep the server in the proper size for placement on an iron or aluminum rack. The rack has a screw hole for the fixed server so that it can be aligned with the screw hole of the server and fixed with screws to facilitate the space required to install each server.

The specified size is the width of the server (48.26cm = 19 inches) and the height (multiple of 4.445cm). Since the width is 19 inches, the rack that satisfies this requirement is sometimes referred to as a "19-inch rack". The thickness is 4.445 cm as the basic unit. The 1U size is 4.445cm, and the 2U size is 1U doubled to 8.89cm.

The so-called "1U PC server" is a product that meets the EIA specifications and has a thickness of 4.445 cm. Products designed to fit into a 19-inch rack are generally referred to as rack servers.