在托管、购买服务器或者租用、使用机柜的时候，有时会听到1U、2U、4U或者42U等类似这样子的名词。而这些名词又代表什么意思呢?跟着快网小编一起来了解一下吧!

　　When hosting, purchasing servers, or renting or using server cabinets, sometimes we hear terms like 1U, 2U, 4U, or 42U. And what do these nouns represent? Follow the Quick Net editor to learn more!

　　关于“U”的单位U是一种表示服务器外部尺寸的单位，是unit的缩略语。规定了服务器的尺寸，可以使服务器以一定的尺寸放在机架上。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，这样子可以方便安装每一部服务器所需要的空间。

　　Regarding the unit of 'U', U is a unit that represents the external dimensions of a server and is an abbreviation for 'unit'. The size of the server is specified, which allows the server to be placed on the rack with a certain size. There are screw holes on the rack to fix the server, so that it can match the screw holes of the server, and then be fixed with screws to facilitate the installation of the required space for each server.

　　1U 2U 4U 服务器服务器规定的尺寸是服务器的宽(48.26cm=19英寸)与高(4.445cm的倍数)，厚度(高度))以4.445cm为基本单位。在机架式服务器尺寸当中，常见的就是1U服务器、2U服务器、4U服务器，这些服务器的尺寸是：1U=4.445厘米，2U=4.445*2=8.89厘米，4U=4.445*4=17.78厘米。在实际使用当中，1U或者2U服务器是经常使用的。因为服务商是根据服务器占用空间来计算费用的，所以采用1U服务器是节省空间的和的，但是1U服务器的扩展性不如2U服务器的好。1U的硬盘数多可以插4个3.5寸，2U可以插8个3.5寸甚更多，另外PCI的插槽数目也不同，1U多2个，2U的可以到6个。

　　The dimensions specified for a 1U 2U 4U server are the width (48.26cm=19 inches) and height (multiples of 4.445cm) of the server, with thickness (height) measured in units of 4.445cm. The common sizes of rack mounted servers are 1U servers, 2U servers, and 4U servers. The dimensions of these servers are: 1U=4.445 centimeters, 2U=4.445 * 2=8.89 centimeters, and 4U=4.445 * 4=17.78 centimeters. In practical use, 1U or 2U servers are the most commonly used. Because service providers calculate fees based on server space occupancy, using a 1U server is the most space saving and cost-effective option. However, the scalability of a 1U server is not as good as that of a 2U server. A 1U hard drive can accommodate up to 4 3.5-inch hard drives, while a 2U can accommodate 8 3.5-inch or even more. Additionally, the number of PCI slots varies, with a maximum of 2 for 1U and up to 6 for 2U.

　　42U机柜42U机柜一般的分类是：1)按宽度分：600mm和800mm宽的42U机柜，深度有：600mm,800mm,900mm,960mm,1000mm,1100mm,1200mm等;2)按实际需求分：除了实际使用尺寸是42U之外，宽度和深度可以按照实际需求定制。一个机柜所放的服务器是有限的，42U高度的机柜并不代表着实际能够放42个1U服务器。放了服务器之后还要留散热和挪动的空间，一些走线的空间，还有放交换机、防火墙、显示器等其他设备的空间。所以一个42U机柜能放多少服务器，需要根据具体的设备来计算。那么问题来了，一个机柜一般部署多少台服务器设备?一个机柜部署的服务器数量，要考虑很多参数，比如服务器的体积、功耗、发热量等物理参数，还需要考虑机柜的供电、冷却、承重等参数，如何确定能部署多少台服务器，做决定时可以参考一下关键参数：1)预留：每个设备间预留1U以便散热，预留交换机位置，考虑PDU位置;2)一般提供冗余10KW电源，静态承载能力不小于1200kg(根据机房建设参数确定)3)不超电的前提下，一个机柜累计设备U数，一般不超过26U一个机柜，全1U设备部署数量一般不超过16台，全2U设备一般不超过12台，全4U设备一般4到7台。

　　The general classification of 42U cabinets is: 1) Divided by width: 600mm and 800mm wide 42U cabinets, with depths of 600mm, 800mm, 900mm, 960mm, 1000mm, 1100mm, 1200mm, etc; 2) According to actual needs: In addition to the actual size of 42U, the width and depth can be customized according to actual needs. The number of servers that can be placed in one cabinet is limited, and a cabinet with a height of 42U does not necessarily mean that 42 1U servers can actually be placed. After installing the server, there should be space for heat dissipation and relocation, some wiring space, and space for other devices such as switches, firewalls, and displays. So how many servers can be placed in a 42U cabinet needs to be calculated based on the specific equipment. So the question is, how many server devices are usually deployed in one cabinet? The number of servers deployed in a cabinet needs to consider many parameters, such as physical parameters such as server volume, power consumption, heat generation, as well as parameters such as power supply, cooling, and load-bearing capacity of the cabinet. When deciding how many servers can be deployed, key parameters can be referred to: 1) Reservation: Reserve 1U between each device for heat dissipation, reserve switch positions, and consider PDU positions; 2) Generally, a redundant 10KW power supply is provided, with a static carrying capacity of not less than 1200kg (determined according to the construction parameters of the computer room). 3) Under the premise of not exceeding the power limit, the cumulative number of equipment U in a cabinet generally does not exceed 26U per cabinet. The deployment of all 1U equipment generally does not exceed 16 units, all 2U equipment generally does not exceed 12 units, and all 4U equipment generally ranges from 4 to 7 units.

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