Editing 19-inch rack (section)

=== Rack unit ===
{{Main|Rack unit}}
Racks are vertically divided into regions, {{convert|44.45|mm|in|2|abbr=}} in height.  Each region has three complete hole pairs on each side. The holes are centered at {{convert|6.35|mm|in|2}}, {{convert|22.25|mm|in|2}}, and {{convert|38.1|mm|in|2}} from the top or bottom of the region. Such a region is commonly known as a '''U''', for ''unit'', '''RU''' for ''rack unit'' or, in German, '''HE''', for ''[[:de:Höheneinheit|Höheneinheit]]''. Heights within racks are measured by this unit. Rack-mountable equipment is usually designed to occupy some integer number of U. For example, an [[oscilloscope]] might be 4U high. Rack-mountable computers and servers are mostly between 1U and 4U high. A [[blade server]] enclosure might require 10U.

Occasionally, one may see fractional U devices such as a 1.5U server or devices that are just 22.5 or 15&nbsp;cm in width, allowing for 2 or 3 such devices to be installed side by side, but these are much less common.

The height of a rack can vary from a few inches, such as in a broadcast console, to a floor-mounted rack whose interior is 45 rack units ({{convert|200.2|cm|in|2|disp=or}}) high. 42U is a common configuration. Many wall-mounted enclosures for industrial equipment use 19-inch racks.