A Rack Unit (U or RU) is the standard height measurement used for mounting equipment in server racks. 5 inches tall, a 4U device is 7 inches tall, and so on. 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. A 1U server rack unit (often written as 1U, 1 RU, or rack unit) is not a standalone product—it's a standardized vertical measurement used exclusively within the context of 19-inch rack systems. This unit governs how. Most professional server racks follow the EIA-310 standard, which defines: These standards make it possible for any 19-inch compatible device to fit securely within the rack, regardless of brand. This article explains definition, planning, installation tips, and trends. The Eurocard specifies a standard rack unit as the unit of height; it also defines a similar unit.
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