What is U size in Server Rack?

You’re likely to hear such phrases as a “1U switch” or a “2U server” during conversations of specialists in an IT sphere. What does the U mean in server racks? This is what we deal with in our article.

What is U in server rack?

Server cabinets and racks are used for accommodating high-precision hardware that controls business tasks. However, the question is how to determine an optimal size of these furniture pieces. For this purpose, a special value was chosen.

A “U” rack dimension stands for a rack unit and means the height of a server furniture piece. This measurement denotes the height of a device accommodated in the server furniture. The “U” in rack size equals to 1,75 inches (or 44.45 mm.). This size is taken to fit all the hardware.

For large hardware that is bigger than 1U, such values as 2U, 6U, 12U are taken. They provide storage for multiple devices or one big piece of equipment.

What is the origin of the server rack U meaning as a standard?

The U meaning can be traced back to the concept of rack units, which emerged as a standard within the server rack industry. This standardization was spearheaded by the Electronic Industries Association (EIA) to streamline compatibility between equipment and server furniture pieces. Without such standards, you might encounter a rail with inconsistent hole spacing, making it incompatible.

The adoption of these standards simplifies the user experience, as it ensures that their existing equipment can seamlessly integrate with any future purchases. Absent these standards, manufacturers might be more inclined to develop proprietary systems, locking customers into their specific product ecosystems.

Although the EIA-310 document can be purchased on the IHS market, you can also refer to manufacturers’ dimensional documents for measurement details. The popular EIA-310-D version, which dates back to 1992, makes it challenging to pinpoint the exact origins of the term ‘rack unit’. However, its widespread use illustrates its significance as a standard in the industry.

Popular Sizes

Common Sizes: 1U, 2U, and 4U

• 1U models mean that the size of hardware accommodated inside is 1,75 inch-high.
• 2U is used for bigger devices. The height of such models is calculated by multiplying 1,75 by 2. Thus, 2U = 3,5 inches. Such cabinets are suitable for more powerful computing systems that require more space inside a furniture piece.
• 4U is designed for even bigger electronic devices, the height of which is 7 inches (4 * 1,75). However, this is not the maximum size. There are also 9U, 12U, and bigger solutions.

Half rack

This dimension is applicable to the width of networking hardware. Furniture pieces have standard frame width equal to 19”. Half rack models mean that the width of the equipment is 9.5”.

Full rack

When determining the number of furniture pieces and answering how many racks should I use for a server, note that servers can be of different sizes. Full models take 19” of the width, which means that a single unit occupies the entire rack or cabinet.

Note that although the height and width of the products are standardized, the depth may vary. Models are produced in several depths.

Table of Units Sizes

In conclusion, understanding what does the U mean in server racks is crucial when selecting the appropriate cabinet size, as it directly impacts the system’s performance and efficiency indicators. The U in rack size represents a unit of measurement used to define the needed space. Proper organization of the internal components within the server cabinet is essential, ensuring adherence to the requirements established for data centers.