The concept of U:
The reason to specify the size of the server is to keep the server in a proper size for placing on an iron or aluminum rack. There are screw holes for fixing the server on the rack, so that it can match the screw holes of the server, and then fix them with screws, so as to facilitate the space required for installing each server.
The specified size is a multiple of the server’s width (48.26cm (19 inches)) and height (1.75inches (4.445cm)). Since the width is 19 inches, sometimes the rack meeting this requirement is called “19 inch rack”. The basic unit of thickness is 4.445cm. 1 u is 4.445cm, 2U is 2 times of 1U, 8.89cm.
The so-called “1U PC server” is a product whose shape meets EIA specifications and thickness is 4.445cm. Products designed to fit into 19 inch cabinets are generally referred to as rack servers.
So what is a 1U server? The so-called 1U server is a low-cost server platform with high availability and high density, which is specially designed for special application industries and high-density computer environment. They can start their own operating system through the local hard disk, such as Windows NT / 2000 / 2003, Linux, Solaris, etc., similar to a separate server. In this mode, each motherboard runs its own system, serves different user groups and has no relationship with each other. However, we can still use the system software to assemble these motherboards into a server cluster.