The shape of the rack-mounted servers do not appear to the computer, such as switches, there are 1U (1U = 1.75 inches = 4.45CM), 2U, 4U and other specifications. Rack-mounted servers installed in a standard 19 in. rack inside. This structure is mostly functional server. For information services companies (such as ISP / ICP / ISV / IDC), select the server must first consider the size, power consumption, heat and other physical parameters of the server because the information services companies typically use large dedicated room unified deployment and management of a large number of server resources, the room is usually equipped with tight security measures, a good cooling system, multiple backup power supply system, the engine room of the cost is quite expensive. To the cost of the service to deploy more servers directly related to the limited space usually use mechanical dimensions conform to the 19-inch industry-standard rack-mounted servers. Rack-mounted servers also have a variety of specifications, such as 1U (4.45cm high), 2U, 4U, 6U, 8U. Usually a 1U rack-mountable servers save space, but the performance and scalability is poor for some of the business is relatively fixed field of use. More than 4U high performance, scalability, and general support for more than four high-performance processor and a large number of standard hot-swappable components. Management is also very convenient, manufacturers usually provide the appropriate management and monitoring tools for critical applications for visits, but the larger the space utilization is not high.