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Physical Infrastructure

Rack Unit

U

Standard unit of vertical height for rack-mounted equipment. 1U = 44.45 mm (1.75 in).

Unit: 44.45 mm per U

Full Definition

A rack unit (U or RU) is the standard vertical measurement for equipment installed in a 19-inch or 21-inch rack enclosure, defined in IEC 60297. One rack unit equals 44.45 mm (1.75 inches). A standard 42U rack is approximately 2 m tall. Equipment is sized in U-height: 1U servers, 2U storage nodes, 4U GPU servers. Rack density — measured in kW per rack — is critical in AI workloads where 80–100 kW per rack is common, requiring liquid cooling solutions.

Also Known As

rack unitru1u2u4u

Source Reference

IEC 60297-3-100 — Mechanical Structures for Electronic Equipment

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