What are 1U, 2U, 4U servers, and 42U cabinets?
May 22, 2023
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When it comes to servers, we often mention 2U servers or 42U servers. So what does "U" mean in servers?
Before answering this question, let's briefly introduce servers.
I. Servers
A server refers to a network device that can provide certain services. The main services provided include data reception and transmission, data storage, and data processing.
In simple terms, we can think of a server as a special computer without a monitor.
Can my personal computer be used as a server?
In theory, a personal computer can be used as a server. However, servers are generally used in specific scenarios, such as financial enterprises, online shopping platforms, etc. Only data centers consisting of thousands of servers can store and process massive amounts of data. Therefore, personal computers cannot meet the special requirements in terms of performance, bandwidth, and data processing capabilities.
Servers can be classified based on their external form:
Tower servers: The most common type of server, similar to a computer's main unit. These servers are large in size, have strong independence, and are not convenient for system management during collaborative work. They are mainly used for small businesses.
Rack servers: They have a standardized appearance and are measured in units of "U" for their height. These servers take up less space, are easy to manage, and are mainly used by enterprises with high server demands. They are also the most commonly used type of server.
Blade servers: They are rack-mounted chassis with a standard height and can accommodate multiple card-like server units. They are mainly used in large-scale data centers or fields that require massive computing power, such as banking and the financial industry.
II. What is "U"?
In server classification, we learned that the height of rack servers is measured in units of "U." So what exactly is "U"?
"U" (abbreviation for "unit") is a unit of measurement for the height dimension of rack-mounted servers. The detailed dimensions of "U" were established by the Electronic Industries Alliance (EIA) in the United States. 1U is equal to 4.445 centimeters, 2U is equal to 4.445 * 2 = 8.89 centimeters, and so on.
"U" is not exclusive to servers but was originally used in rack structures for communication exchanges and later referenced in server racks. It is currently used as an informal standard for server rack structures, including specifications for screw sizes, hole spacing, slide rails, and more.
By specifying server dimensions in "U," servers can maintain appropriate sizes for installation on iron or aluminum racks. The rack is pre-drilled with screw holes according to different server sizes, allowing it to align with the server's screw holes and be securely fastened.
The dimensions specified by "U" are the width (48.26 centimeters = 19 inches) and height (multiples of 4.445 centimeters) of the server. The height of the server is measured in basic units of "U," where 1U = 4.445 centimeters. Since the width is 19 inches, racks that meet this specification are sometimes referred to as "19-inch racks."
III. 1U servers, 2U servers, 4U servers
In rack-mounted servers, the most common servers are:
1U server: Server height is 4.445 centimeters.
2U server: Server height is 4.445 * 2 = 8.89 centimeters.
4U server: Server height is 4.445 * 4 = 17.78 centimeters.
The appearance of rack-mounted servers doesn't resemble computers but rather switches. Rack-mounted servers are installed in standard 19-inch cabinets. This type of structure is mostly used for functional servers.
In practical use, 1U or 2U servers are the most commonly used servers.
Since service providers calculate costs based on server space usage, using 1U servers is the most space-saving and cost-effective option. 1U servers have less scalability compared to 2U servers, with a maximum of 4 hard drives and 2 PCI slots. On the other hand, 2U servers offer better scalability than 1U servers, supporting up to 8 hard drives and up to 6 PCI slots.
IV. 19-inch cabinets
In daily use, our personal computers are placed on the floor or desk, but servers are housed in specialized cabinets called "server racks" or "server enclosures". Cabinets come in different sizes, but the most common ones are 19-inch standard cabinets.
A 19-inch standard cabinet is designed to accommodate 19-inch rack-mounted servers. 19 inches is equivalent to 48.26 centimeters and refers to the width of the server, specifically the distance between the two mounting ears of rack-mounted equipment. This is the current structural standard for most rack-mounted equipment.
When installing equipment in a 19-inch standard cabinet, the height of the equipment is represented by the unit "U," where 1U = 4.445 centimeters.
Devices designed for 19-inch standard cabinets have their front panels manufactured according to specifications in nU (n represents integers starting from 1). For non-standard devices, they can generally be fitted into a 19-inch chassis and secured using additional adapter brackets.
Due to the 19-inch width of many industrial-grade devices, 19-inch cabinets are the most commonly used standard cabinets.
V. 42U cabinets
In addition to the 19-inch standard cabinets, another common type of standard cabinet is the 42U cabinet.
The classification of 42U cabinets includes:
Based on width and depth: 42U cabinets with widths of 600mm and 800mm, and depths of 600mm, 800mm, 900mm, 960mm, 1000mm, 1100mm, 1200mm, etc.
Based on actual requirements: Besides the actual size of 42U, the width and depth can be customized according to specific needs.
According to the theory above, we can infer that a 42U cabinet should be able to accommodate 42 1U servers. However, in reality, the number of servers that can be placed in a 42U cabinet depends on the specific equipment.
This is because a 42U cabinet needs to reserve space for heat dissipation, movement, cabling, and other devices such as switches, firewalls, monitors, etc.
VI. Summary
Finally, let's summarize the new knowledge we have acquired today:
There are three types of servers: tower servers, rack-mounted servers, and blade servers.
Servers are typically represented using "U," where 1U = 4.445 centimeters.
Common rack-mounted servers include 1U, 2U, and 4U.
Common standard cabinets include 19-inch cabinets and 42U cabinets.
Servers are frequently placed in standard 19-inch cabinets.
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