A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is wide. The 19 inch dimension includes the edges or "ears" that protrude from each side of the equipment, allowing the module to be fastened to the rack frame with screws or bolts. Common uses include
computer servers,
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
s equipment and
networking hardware
Networking hardware, also known as network equipment or computer networking devices, are electronic devices which are required for communication and interaction between devices on a computer network. Specifically, they mediate data transmission in ...
,
audiovisual
Audiovisual (AV) is electronic media possessing both a sound and a visual component, such as slide-tape presentations, films, television programs, corporate conferencing, church services, and live theater productions.
Audiovisual service prov ...
production gear, and
scientific equipment
A scientific instrument is a device or tool used for scientific purposes, including the study of both natural phenomena and theoretical research.
History
Historically, the definition of a scientific instrument has varied, based on usage, laws, an ...
.
Overview and history
Equipment designed to be placed in a rack is typically described as rack-mount, rack-mount instrument, a rack-mounted system, a rack-mount chassis, subrack, rack cabinet, rack-mountable, or occasionally simply shelf. The height of the electronic modules is also standardized as multiples of or one
rack unit
A rack unit (abbreviated U or RU) is a unit of measure defined as . It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby th ...
or U (less commonly RU). The industry-standard rack cabinet is 42U tall; however, 45U racks are also common.
The term ''relay rack'' appeared first in the world of
telephony
Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
.
By 1911, the term was also being used in
railroad signaling
Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed Rail tracks, rails, making them uniquely susceptible to collision. This susceptibility is exacerbated b ...
. There is little evidence that the dimensions of these early racks were standardized.
Telephone equipment racks (1923)
The 19-inch rack format with rack-units of was established as a standard by AT&T around 1922 in order to reduce the space required for
repeater
In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some ...
and termination equipment in a telephone company
central office. The earliest repeaters from 1914 were installed in ad hoc fashion on shelves, in wooden boxes and cabinets. Once serial production started, they were built into custom-made racks, one per repeater. But in light of the rapid growth of the toll network, the engineering department of AT&T undertook a systematic redesign, resulting in a family of modular factory-assembled panels all "designed to mount on vertical supports spaced 19 inches between centers. The height of the different panels will vary, ... but ... in all cases to be a whole multiple of 1 inches".
By 1934, it was an established standard with holes
tapped for
12-24 screws with alternating spacings of and The EIA standard was revised again in 1992 to comply with the
1988 public law 100-418, setting the standard U as + + , making each "U" .
The 19-inch rack format has remained constant while the technology that is mounted within it has changed considerably and the set of fields to which racks are applied has greatly expanded. The standard rack arrangement is widely used throughout the
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
,
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...
,
audio
Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to:
Sound
*Audio signal, an electrical representation of sound
*Audio frequency, a frequency in the audio spectrum
*Digital audio, representation of sound ...
,
video
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syste ...
,
entertainment
Entertainment is a form of activity that holds the attention and interest of an audience or gives pleasure and delight. It can be an idea or a task, but is more likely to be one of the activities or events that have developed over thousa ...
and other industries, though the
Western Electric
The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...
23-inch standard, with holes on centers, is still used in legacy
ILEC/
CLEC facilities.
![DE-CIX GERMANY - Switch Rack (6218137120)](https://upload.wikimedia.org/wikipedia/commons/1/1a/DE-CIX_GERMANY_-_Switch_Rack_%286218137120%29.jpg)
Nineteen-inch racks in two-post or four-post form hold most equipment in modern
data centers
A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunic ...
,
ISP
An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...
facilities, and professionally designed corporate
server room
A server room is a room, usually air-conditioned, devoted to the continuous operation of computer servers. An entire building or station devoted to this purpose is a data center.
The computers in server rooms are usually headless systems that c ...
s. They allow for dense hardware configurations without occupying excessive floorspace or requiring shelving.
![Tektronix oscilloscope 7603 in 19 inch rack version with three plug-ins](https://upload.wikimedia.org/wikipedia/commons/3/39/Tektronix_oscilloscope_7603_in_19_inch_rack_version_with_three_plug-ins.jpg)
Nineteen-inch racks are also often used to house professional audio and video equipment, including
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost the v ...
s,
effects unit
An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing.
Common effects include distortion/overdrive, often used with electric guitar in el ...
s, interfaces,
headphone
Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an au ...
amplifiers, and even small scale audio mixers. A third common use for rack-mounted equipment is
industrial power, control, and automation hardware.
Typically, a piece of equipment being installed has a front panel height inch () less than the allotted number of Us. Thus, a 1U rackmount computer is not tall but is tall. If ''n'' is number of rack units, the ideal formula for panel height is h = (1.75''n'' − 0.031) for calculating in inches, and h = (44.45''n'' − 0.794) for calculating in millimetres. This gap allows a bit of room above and below an installed piece of equipment so it may be removed without binding on the adjacent equipment.
Equipment mounting
Fastening
Originally, the mounting holes were
tapped with a particular screw thread. When rack rails are too thin to tap,
rivnut
A rivet nut, also known as a blind rivet nut, or rivnut, is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. It is a kind of threaded insert. There are two types: one is designed to for ...
s or other
threaded insert
A threaded insert, also known as a threaded bushing, is a fastener element that is inserted into an object to add a threaded hole. They may be used to repair a stripped threaded hole, provide a durable threaded hole in a soft material, place a thr ...
s can be used, and when the particular class of equipment to be mounted is known in advance, some of the holes can be omitted from the mounting rails.
Threaded mounting holes in racks where the equipment is frequently changed are problematic because the threads can be damaged or the mounting screws can break off; both problems render the mounting hole unusable. Tapping large numbers of holes that may never be used is expensive; nonetheless tapped-hole racks are still in use, generally for hardware that rarely changes. Examples include telephone exchanges, network cabling panels, broadcast studios and some government and military applications.
The tapped-hole rack was first replaced by clearance-hole (Round Hole, Round Unthreaded Holes, and Versa Rail) racks. The holes are large enough to permit a bolt to be freely inserted through without binding, and bolts are fastened in place using
cage nut
A cage nut or caged nut (also called a captive or clip nut) consists of a (usually square) nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes, for ...
s. In the event of a nut being stripped out or a bolt breaking, the nut can be easily removed and replaced with a new one. Production of clearance-hole racks is less expensive because tapping the holes is eliminated and replaced with fewer, less expensive, cage nuts.
The next innovation in rack design has been the square-hole rack. Square-hole racks allow boltless mounting, such that the rack-mount equipment only needs to insert through and hook down into the lip of the square hole. Installation and removal of hardware in a square hole rack is very easy and boltless, where the weight of the equipment and small retention clips are all that is necessary to hold the equipment in place. Older equipment meant for round-hole or tapped-hole racks can still be used, with the use of cage nuts made for square-hole racks.
Structural support
Rack-mountable equipment is traditionally mounted by bolting or clipping its front panel to the rack. Within the IT industry, it is common for network/communications equipment to have multiple mounting positions, including table-top and wall mounting, so rack-mountable equipment will often feature L-brackets that must be screwed or bolted to the equipment prior to mounting in a 19-inch rack. With the prevalence of
23-inch racks in the Telecoms industry, the same practice is also common, but with equipment having 19-inch and 23-inch brackets available, enabling them to be mounted in existing racks.
A key structural weakness of front-mounted support is the bending stress placed on the mounting brackets of the equipment, and the rack itself. As a result, 4-post racks have become common, featuring a mirrored pair of rear mounting posts. Since the spacing between the front and rear mounting posts may differ between rack vendors and/or the configuration of the rack (some racks may incorporate front and rear rails that may be moved forwards and backwards, e.g. APC SX-range racks), it is common for equipment that features 4-post mounting brackets to have an adjustable rear bracket.
Servers and deep pieces of equipment are often mounted using rails that are bolted to the front and rear posts (as above, it is common for such rails to have an adjustable depth), allowing the equipment to be supported by four posts, while also enabling it to be easily installed and removed.
Although there is no standard for the depth of equipment, nor specifying the outer width and depth of the rack enclosure itself (incorporating the structure, doors and panels that contain the mounting rails), there is a tendency for 4-post racks to be or wide, and for them to be , or deep. This of course varies by manufacturer, the design of the rack and its purpose, but through common constraining factors (such as raised floor tile dimensions), these dimensions have become quite common. The extra width and depth enables cabling to be routed with ease (also helping to maintain bend-radius for fibre and copper cables) and deeper equipment to be utilised. A common feature in IT racks are mounting positions for "Zero-U" accessories, such as PDUs (
power distribution unit
A power distribution unit (PDU) is a device fitted with multiple outputs designed to distribute electric power, especially to racks of computers and networking equipment located within a data center. Data centers face challenges in power protec ...
s) and vertical cable managers/ducts, that utilise the space between the rear rails and the side of the rack enclosure.
The strength required of the mounting posts means they are invariably not merely flat strips but actually a wider folded strip arranged around the corner of the rack. The posts are usually made of
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
of around 2 mm thickness (the official standard recommends a minimum of 1.9 mm), or of slightly thicker
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
.
Racks, especially two-post racks, are often secured to the floor or adjacent building structure so as not to fall over. This is usually required by local building codes in
seismic zones
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
. According to
Telcordia Technologies
iconectiv is a supplier of network planning and network management services to telecommunications providers. Known as Bellcore after its establishment in the United States in 1983 as part of the break-up of the Bell System, the company's name ...
Generic Requirements document GR-63-CORE, during an earthquake, telecommunications equipment is subjected to motions that can over-stress equipment framework, circuit boards, and connectors. The amount of motion and resulting stress depends on the structural characteristics of the building and framework in which the equipment is contained, and the severity of the earthquake. Seismic racks rated according to
GR-63 ''NEBS Requirements: Physical Protection,'' are available, with Zone 4 representing the most demanding environment
GR-3108 ''Generic Requirements for Network Equipment in the Outside Plant (OSP),'' specifies the usable opening of seismic-compliant 19-inch racks.
Rails (slides)
Heavy equipment or equipment which is commonly accessed for servicing, for which attaching or detaching at all four corners simultaneously would pose a problem, is often not mounted directly onto the rack but instead is mounted via rails (or slides). A pair of rails is mounted directly onto the rack, and the equipment then slides into the rack along the rails, which support it. When in place, the equipment may also then be bolted to the rack. The rails may also be able to fully support the equipment in a position where it has been slid clear of the rack; this is useful for inspection or maintenance of equipment which will then be slid back into the rack. Some rack slides even include a tilt mechanism allowing easy access to the top or bottom of rack-mounted equipment when it is fully extended from the rack.
Slides or rails for computers and other data processing equipment such as
disk array
A disk array is a disk storage system which contains multiple disk drives. It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID, deduplication, encryption and virtualization.
Compone ...
s or
routers often need to be purchased directly from the equipment manufacturer, as there is no standardization on such equipment's thickness (measurement from the side of the rack to the equipment) or means for mounting to the rail.
A rails kit may include a cable management arm (or CMA), which folds the cables attached to the server and allows them to expand neatly when the server is slid out, without being disconnected.
Computer mounting
Computer servers designed for rack-mounting can include a number of extra features to make the server easy to use in the rack:
* The sliding rails can lock in various extended positions to prevent the equipment from moving when extended out from the rack for service.
* The server itself might have locking pins on the sides that just drop into slots on the extended rail assembly, in a manner similar to a removable kitchen drawer. This permits very easy server installation and removal since there is no need for the server to be held in midair while someone fastens each rail to the sides of the server with screws.
* Some manufacturers of rack-mount hardware include a folding cable tray behind the server, so that the cables are held into a neat and tidy folded channel when inside the rack, but can unfold out into a long strip when pulled out of the rack, allowing the server to continue to be plugged in and operating normally even while fully extended and hanging in mid-air in front of the rack. This piece of equipment thus simplifies maintenance, but at the cost of providing a restriction to airflow.
* Rack-optimized servers might duplicate indicator lights on the front and rear of the rack to help identify a machine needing attention, or provide separate "identify"
LED
A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
indicators on both sides of the server (which can be turned on in software or by pushing an associated button). Since some configurations permit over fifty 1U servers in a single rack, this provides a simple method to determine exactly which machine is having a problem when at the rear of the rack.
* A handle may be provided at the rear of the server rails, to help pull or push the server without having to pull on the cables.
When there is a large number of computers in a single rack, it is impractical for each one to have its own separate keyboard, mouse, and monitor. Instead, a
KVM switch
A KVM switch (with KVM being an abbreviation for "keyboard, video, and mouse") is a hardware device that allows a user to control multiple computers from one or more sets of keyboards, video monitors, and mice.
Name
Switches to connect mu ...
or
LOM software is used to share a single keyboard/video/mouse set amongst many different computers.
Since the mounting hole arrangement is vertically symmetric, it is possible to mount rack-mountable equipment upside-down. However, not all equipment is suitable for this type of mounting. For instance, most
optical disc
In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces. ...
players will not work upside-down because the driving
motor
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
mechanism does not grip the disc.
Rack types
19-inch server racks can vary in qualities. A standard 19-inch server rack cabinet is typically 42u in height, wide, and deep. Newer server rack cabinets come with adjustable mounting rails allowing the user to place the rails at a shorter depth if needed. There are a multitude of specialty server racks including soundproof server racks, air conditioned server racks, NEMA rated, seismic rated, open frame, narrow, and even miniature 19-inch racks for smaller applications. Cabinets are generally sized to be no wider than the standard floor tiles used in most data centers.
Racks carrying telecom equipment like routers and switches often have extra width to accommodate the many cables on the sides.
Four-post cabinet racks
''Four-post racks'' allow for mounting rails to support the equipment at the front and rear. These racks may be open in construction without sides or doors, or may be enclosed by front and/or rear doors, side panels, and tops. Most data centers use four-post racks.
Two-post relay racks
''Two-post racks'' provide two vertical posts. These posts are typically heavy gauge metal or extruded aluminum. A top bar and wide foot connect the posts and allow the rack to be securely attached to the floor and/or roof for seismic safety. Equipment can be mounted either close to its center of gravity (to minimize load on its front panel), or via the equipment's front panel holes.
The ''Relay Racks'' name comes from early two-post racks which housed telephone relay and switching equipment. Two-post racks are most often used for telecommunication installations.
ATA road case racks
![Amps (QuadFest) (edited)](https://upload.wikimedia.org/wikipedia/commons/0/0a/Amps_%28QuadFest%29_%28edited%29.jpg)
19-inch equipment that needs to be moved often or protected from harsh treatment can be housed in an
Air Transport Association of America
Airlines for America (A4A), formerly known as Air Transport Association of America (ATA), is an American trade association and lobbying group based in Washington, D.C. that represents major North American airlines.
Profile
Mission
A4A ...
(ATA) approved
road case
A road case, ATA case or flight case is a shipping container specifically built to protect musical instruments, motion picture equipment, audio and lighting production equipment, properties, firearms, or other sensitive equipment when it must be ...
sometimes also referred to as flight case. Road cases typically have plywood sides laminated with
polyvinyl chloride (PVC), extruded aluminum edges, steel corners, handles, and latches. Larger cases typically have wheels for easy transport. Road case racks come in different heights based on the 1U standard and different depths. Non-isolated cases simply mount 19-inch mounting posts inside the case. To protect equipment from shock and vibration road rack cases use an inner and outer case. These cases can be isolated by thick layers of foam or may use spring-loaded shock mounting. Touring musicians, theatrical productions and sound and light companies use road case racks.
Fiberglass reinforced plastic case racks
In 1965, a durable
fiber reinforced plastic
Fibre-reinforced plastic (FRP; also called fibre-reinforced polymer, or in American English ''fiber'') is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fib ...
19-inch rackmount case was patented by ECS Composites and became widely used in military and commercial applications for electronic deployment and operation. State-of-the-art rackmount cases are now also constructed of thermo stamped composite,
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
, and
DuPont
DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
's
Kevlar
Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s a ...
for demanding military and commercial uses.
Polyethylene molded case racks
Portable rack cases using a rotary-molded
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
outer shell are a lower-cost alternative to the more durable ATA-approved case. These cases are marketed to musicians and entertainers for equipment not subject to frequent transportation and rough handling. The polyethylene shell is not fiberglass reinforced and is not rigid. The shape of small cases is maintained by the rack rails and the cover seal extrusions alone. Larger cases are further reinforced with additional plywood or sheet metal. The outer shell is frequently embossed in a self-mating pattern to combat the tendency for stacked cases to deform slightly creating a slope that encourages the upper case to slide off. The cases typically use extruded aluminum bands at the ends of the body with tongue-and-groove mating to like bands for the covers. End covers are typically secured with either a simple draw latch or a rotary cam "butterfly" latch, named for the shape of the twist handle.
Cooling
There is no standard for airflow and cooling of rack-mounted equipment. A variety of airflow patterns can be found, including front intakes and rear exhausts, as well as side intakes and exhausts. Low-wattage devices may not employ active cooling, but use only passive thermal radiation and
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
to dissipate heat.
For rack-mounted computer servers, devices generally intake air on the front and exhaust on the rear. This prevents circular airflows where hot exhaust air is recirculated through an adjacent device and causes overheating.
Although open-frame racks are the least expensive, they also expose air-cooled equipment to dust, lint, and other environmental contamination. An enclosed sealed cabinet with forced air fans permits air filtration to protect equipment from dust.
Large server rooms will often group rack cabinets together so that racks on both sides of an aisle are either front-facing or rear-facing, which simplifies cooling by supplying cool air to the front of the racks and collecting hot air from the rear of the racks. These aisles may themselves be enclosed into a cold air containment tunnel so that cooling air does not travel to other parts of the building where it is not needed or mixes with hot air, making it less efficient.
Raised or false floor cooling in server rooms can serve a similar purpose; they permit cooling airflow to equipment through the underfloor space to the underside of enclosed rack cabinets.
A difficulty with forced air fan cooling in rack equipment is that fans can fail due to age or dust. The fans themselves can be difficult to replace. In the case of network equipment, it may be necessary to unplug 50 or more cables from the device, remove the device from the rack, and then disassemble the device chassis to replace the fans.
However, some rack equipment has been designed to make fan replacement easy, using quick-change fan trays that can be accessed without removing the cabling or the device from the rack, and in some cases without turning off the device so that operation is uninterrupted during replacement.
Specifications
The formal standards for a rack are available from the following:
*
Electronic Industries Alliance
The Electronic Industries Alliance (EIA; until 1997 Electronic Industries Association) was an American standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They devel ...
EIA-310-D, Cabinets, Racks, Panels, and Associated Equipment, dated September 1992. (Latest Standard Now REV E 1996)
*
Consumer Electronics Association
The Consumer Technology Association (CTA) is a standard and trade organization representing 1,376 consumer technology companies in the United States. CTA works to influence public policy, holds events such as the Consumer Electronics Show (CES ...
CEA-310-E design requirements for Cabinets, Panels, Racks and Subracks., dated December 14, 2005
*
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
- Multiple documents are available in French and English versions.
** IEC 60297 ''Mechanical structures for electronic equipment - Dimensions of mechanical structures of the 482,6 mm (19 in) series''
*** IEC 60297-1 Replaced by IEC 60297-3-100
*** IEC 60297-2 Replaced by IEC 60297-3-100
*** IEC 60297-3-100 ''Part 3-100: Basic dimensions of front panels, subracks, chassis, racks and cabinets''
*** IEC 60297-3-101 ''Part 3-101: Subracks and associated plug-in units''
*** IEC 60297-3-102 ''Part 3-102: Injector/extractor handle''
*** IEC 60297-3-103 ''Part 3-103: Keying and alignment pin''
*** IEC 60297-3-104 ''Part 3-104: Connector dependent interface dimensions of subracks and plug-in units''
*** IEC 60297-3-105 ''Part 3-105: Dimensions and design aspects for 1U chassis''
*** IEC 60297-4 Replaced by IEC 60297-3-102
*** IEC 60297-5 Multiple documents, -100, 101, 102, ... 107, replaced by IEC 60297-3-101
*
Deutsches Institut für Normung
' (DIN; in English, the German Institute for Standardisation Registered Association) is the German national organization for standardization and is the German ISO member body. DIN is a German Registered Association ('' e.V.'') headquartered in ...
DIN 41494 - Multiple documents in German but some documents are available in English.
** DIN 41494 ''Equipment practices for electronic equipment; mechanical structures of the 482,6 mm (19 inch) series''
*** DIN 41494-7 ''Dimensions of cabinets and suites of racks''.
*** DIN 41494-8 ''Components on front panels; mounting conditions, dimensions''
*** DIN IEC 60297-3-100 (see above in IEC section)
A rack's mounting fixture consists of two parallel metal strips (also referred to as "posts" or "panel mounts") standing vertically. The posts are each wide, and are separated by a gap of , giving an overall rack width of . The posts have holes in them at regular intervals, with both posts matching, so that each hole is part of a horizontal pair with a center-to-center distance of .
The holes in the posts are arranged vertically in repeating sets of three, with center-to-center separations of , , . The hole pattern thus repeats every .
Holes so arranged can either be tapped (usually 10-32
UNF thread, or, less often, 6mm
metric
Metric or metrical may refer to:
* Metric system, an internationally adopted decimal system of measurement
* An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement
Mathematics
In mathema ...
) or have square holes for
cage nut
A cage nut or caged nut (also called a captive or clip nut) consists of a (usually square) nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes, for ...
s.
Rack unit
Racks are vertically divided into regions, in height. Each region has three complete hole pairs on each side. The holes are centered at , , and 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 ''
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
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
might be 4U high. Rack-mountable computers and servers are mostly between 1U and 4U high. A
blade server
A blade server is a stripped-down server computer with a modular design optimized to minimize the use of physical space and energy. Blade servers have many components removed to save space, minimize power consumption and other considerations, whil ...
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 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 () high. 42U is a common configuration. Many wall-mounted enclosures for industrial equipment use 19-inch racks.
Related standards
10-inch rack
![19 inch vs 10 inch rack dimensions](https://upload.wikimedia.org/wikipedia/commons/8/84/19_inch_vs_10_inch_rack_dimensions.svg)
Some telecommunications and networking equipment is available in a narrower 10" format with the same unit-height as a standard 19"-rack.
11-foot frame
Frames for holding rotary-dial telephone equipment were generally high. A series of studies led to the adoption of frames high, with modular widths in multiples of —most often wide.
ETSI rack
![Dimensions 19-inch ETSI rack](https://upload.wikimedia.org/wikipedia/commons/b/bc/Dimensions_19-inch_ETSI_rack.png)
The ETSI rack is defined by the
European Telecommunications Standards Institute
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of Information and communications technology, information and communications. ETSI supports the developmen ...
(ETS 300 119). The distance of the right edge of the right mounting rail to the left edge of the left mounting rail is . As 535 mm is very close to 21 inches, these racks are sometimes called 21-inch racks. The gap between the posts is . As 19-inch equipment has a maximum width of , they can easily be mounted in an ETSI rack by means of an ETSI bracket or adapter plate.
In contrast to the "19-inch world", ETSI also defined the size of the rack enclosure: the four allowed widths are and two allowed depths are . Hole spacing is .
23-inch rack
![SSEM Manchester museum close up](https://upload.wikimedia.org/wikipedia/commons/2/21/SSEM_Manchester_museum_close_up.jpg)
A rack is used for housing
telephone
A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
(primarily),
computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
,
audio
Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to:
Sound
*Audio signal, an electrical representation of sound
*Audio frequency, a frequency in the audio spectrum
*Digital audio, representation of sound ...
, and other equipment though is less common than the 19-inch rack. The size denotes the width of the faceplate for the installed equipment. The
rack unit
A rack unit (abbreviated U or RU) is a unit of measure defined as . It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby th ...
is a measure of vertical spacing and is common to both the 19 and 23 inch racks.
Hole spacing is either on centers (Western Electric standard), or the same as for racks ( spacing).
Open Rack
Open Rack is a mounting system designed by
Facebook
Facebook is an online social media and social networking service owned by American company Meta Platforms. Founded in 2004 by Mark Zuckerberg with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin M ...
's
Open Compute Project
The Open Compute Project (OCP) is an organization that shares designs of data center products and best practices among companies, including ARM, Meta, IBM, Wiwynn, Intel, Nokia, Google, Microsoft, Seagate Technology, Dell, Rackspace, Hewlett Pack ...
that has the same outside dimensions as typical 19-inch racks (e.g. 600 mm width), but supports wider equipment modules of .
Gallery
Pictures of 19 inch racks
See also
*
Data center
A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunic ...
*
Horizontal pitch
Horizontal pitch (HP) is a unit of length defined by the Eurocard printed circuit board standard used to measure the horizontal width of rack mounted electronic equipment, similar to the rack unit (U) used to measure vertical heights of rack mount ...
*
Rack unit
A rack unit (abbreviated U or RU) is a unit of measure defined as . It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby th ...
*
Transit case
A transit case is a hard-sided case intended for protecting and concealing defined contents during transportation. In some forms, the interior is filled with foam which has pockets molded or cut into it that equipment specifically fits into. So ...
, for rack cases
*
Open Compute Project
The Open Compute Project (OCP) is an organization that shares designs of data center products and best practices among companies, including ARM, Meta, IBM, Wiwynn, Intel, Nokia, Google, Microsoft, Seagate Technology, Dell, Rackspace, Hewlett Pack ...
, wider, deeper rack design
References
External links
*
{{List of IEC standards
Computer enclosure
Mechanical standards
Server hardware
American inventions
1922 introductions