2U

2U (often written as 2U) is a rack unit height used to classify 19-inch rack-mount equipment. Each rack unit, or "U," measures 1.75 inches (44.45 mm), so a 2U enclosure is 3.5 inches tall (88.9 mm). The width of equipment in standard racks is fixed at 19 inches (482.6 mm), while depth varies by model.

The 2U form factor is common for servers, storage, and network appliances. It provides more internal volume than 1U hardware, allowing dual-processor configurations, increased memory, better airflow, and more drive bays or expansion slots, while maintaining compatibility with standard racks. Drive configurations vary by model, but typical 2U servers offer four to eight 2.5-inch drives or four 3.5-inch drives, along with options for hot-swappable trays, redundant power supplies, and multiple PCIe expansion slots. Some models also support graphics processing units or additional PCIe GPUs.

In enterprise use, 2U servers are deployed for virtualization, databases, and other demanding workloads that benefit from greater expandability without moving to a larger full-height chassis. Notable examples of 2U servers include models from major vendors such as Dell’s PowerEdge R-Series (e.g., R740/R740xd), HP/ Hewlett Packard Enterprise’s ProLiant DL380 Gen9/Gen10 series, and Lenovo’s ThinkSystem SR650 family, among others. In addition to servers, 2U enclosures are used for certain storage arrays and network appliances designed to fit into standard 19-inch racks.

See also: rack unit, 1U, 4U, 19-inch rack.