A 19-inch rack** (or rack, cabinet or closet) (also written 19") is a metal support intended to house electronic, computer and communications equipment. The measurements for the width are standardized "Standard (technology)") to be compatible with equipment from different manufacturers, and is stipulated at 19 inches or 482 mm. They are also called cabinets, cabinets or closets.

Racks for mounting servers have a standard width of 600 millimeters (mm) and a depth of 600, 800, 900, 1000 and even 1200 mm. The 600mm width for server racks matches the standard tile size in data centers. In this way it is very easy to make space distributions in data centers (CPD). For wiring, 800 mm wide racks are also used, when it is necessary to have sufficient lateral space for cable routing.

Racks are used in data processing centers, where space is scarce and a large number of devices need to be accommodated. These devices are usually:

The equipment simply slides on a horizontal rail and is secured with screws. There are also trays that allow non-standardized equipment to be supported, for example, a desktop router.

The specifications of a standard rack are found under the equivalent standards DIN 41494") part 1 and 7, UNE-20539") part 1 and part 2 and IEC 297 part 1 and 2, EIA 310-D and must comply with the RoHS environmental regulations.

The racks are divided into regions 1¾ inches high (44.45 millimeters). In each region there are three holes that follow a symmetrical order. This region is called height or U. The vertical space measures 15.875 mm in height each, for a total of 31.75 mm (1¼ inches). They are 450.85 mm (17¾ inches) apart and make a total of 482.6 mm (exactly 19 inches). Each column has holes at regular intervals called rack units (U) grouped three by three. Vertically, the height of the racks is standardized and their external dimensions are 200 mm by 200 mm. The normal thing is that they exist from 4 U in height to 46/47 U in height.

That is to say, a 41 U or 42 U rack, for example, can never exceed 2000 mm in external height. This ensures that the racks in a room have practically similar dimensions even though they are from different manufacturers.

The heights normally available, according to regulations, would be 800, 1000, 1200, 1400, 1600, 1800, 2000 and 2200 mm.

The depth of the frame is not standardized, as this gives some flexibility to the equipment. However, it is usually 600, 800, 900, 1000 and even 1200 mm.

There are also wall racks that comply with the 19-inch format and have total depths of 300, 400, 450, 500, 550 and 600 mm, being very useful for small installations.