Usually, equipment like servers, routers, and switches is designed in multiples of rack units—for example, 1U, 2U, or 4U—each denoting the amount of vertical space that they occupy in a rack. To illustrate, a 2U device will occupy the same space as two 1U devices in the rack. The height of a rack is measured in Rack Units, written as U. Important: U describes height only, but a server's real "capabilities" are also determined by chassis depth, internal layout, airflow, rails, power, and expansion (PCIe/risers, NVMe. What is a Rack Unit (U)? A Rack Unit (often referred to as just “U”) is the unit of measure that equipment racks use to describe the vertical space they have. One rack unit is equal to a height of 1. The adoption of this standard in the industry ensured that different. What Is 1U, 2U, 3U, 4U, 5U, 6U, and 7U? The 1U, 2U, 3U, 4U, 5U, 6U and 7U are all different sized rackmount servers, and the "U" following the number is short for unit.
[PDF Version]