9010 RMA (Rack Mount Accessory), a 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules.

Equipment designed to be placed in a rack is typically described as rack-mount or simply chassis; the height of the electronic modules is standardized as multiples of 1.75 inches (44.5 mm) or one rack unit or “U”.

Each module has a front panel that is 19 inches (482.6 mm) wide, including edges that protrude on each side which allow the module to be fastened to the rack frame with screws.