The standard for open frame or enclosed cabinets used for the mounting of electronic equipment. Equipment must have a front panel that is 19 inches wide, including edges or ears that protrude on each side which allow the equipment piece to be mounted to the rack frame with screws. 19-inch racks in 2 post or 4 post form hold most equipment in modern data centers, ISP facilities and corporate server rooms.
The height of equipment is described as being measured in the U, for one rack unit, which is 1.75 inches.
Front Mount vs Four Post
A front mount rack is a two post rack where equipment is mounted by the front plate of the equipment only, thus leaving the rest of the unit to hang behind the front plate. A key structural weakness of front-mounted support is the shear stress placed on the mounting rails and the leading edge of the equipment. As a result, 4-post racks have become common, with such racks featuring a mirrored pair of rear mounting posts.
Servers and deep pieces of equipment are often mounted using rails that are bolted to the front and rear posts. There is no standard for the depth of equipment, nor specifying the outer width and depth of the rack enclosure itself.
Dimensions
The standard electronic unit for mounting is 19" wide on the front plate. Behind the plate the remainder of the unit has to be less wide as to slide in between the posts. This width tends to be 16½ wide.
- 16½" Equipment case chassis width
- 19" Equipment front plate width