As you know, server rack many professional rack-mounted network devices are based on the structure of (mostly flat, like a drawer), such as switches, routers, hardware firewall such. The reason why these devices have such a structure type, because they are designed according to international standard rack, so everyone on the basic unity of the plane size can be put together in a large installation of vertical standard cabinet. The advantages are obvious: on the one hand can make the device takes up minimal space, on the other hand to facilitate connections with other network equipment and management, while the engine room will look clean and beautiful.
　　Server rack width is 19 inches in height in units of U (1U = 1.75 inch = 44.45 mm), usually 1U, 2U, 3U, 4U, 5U, 7U several standard server. Cabinet size is the use of common industry standard, usually ranging from 22U to 42U; U rack height by sliding a removable trailer, according to their own server, the user can flexibly adjust the height of the elevation to storage servers, hubs , the disk array cabinets and other network devices. Server is placed well, it's all I / O lines all leads from the rear of the cabinet (rack servers are behind all the interfaces), a unified cabinet trays placed in the general label affixed, easy to manage.
　　Now many of the Internet web server is actually hosted by a unified professional organization, and the website is in fact only a web page maintenance, hardware and network connection to the host agency, so the trustee will be managed according to the height of the server to collect cost, 1U server in hosting fees when a lot cheaper than 2U, which is why the structure of the server now widely used in Internet business.
　　Another point to say that because the server rack server space much smaller than the tower, so this type of server scalability and cooling issues subject to certain restrictions, accessories is also subject to certain screening, are generally too full of equipment can not be achieved expansion, so the stand-alone performance is more limited, more limited scope of application, can only focus on one aspect of the application, such as remote storage and Web services, etc., but a lot of accessories that can not use ordinary tower server model, The advantages of their own have little space, so the rack-mounted server is generally the same configuration than the 20-30% of your tower server. As for the expansion of space caused by small problems, is not without a solution, the use of rack-mounted way, so add a host more in the cabinet is a very easy thing to do, and then through the server handle clustering technology can be achieved capabilities, the use of an external enclosure if it is the way to achieve large-scale expansion, but due to the limited performance of stand-alone rack-mounted server, so the expansion is the unilateral ability to get after the doubling, so only one type of server kind of application is relatively good, we put it classified as a function of the server, this server is highly targeted, generally can not be moved to do it with.