Rack Mounting FAQ

19 inch racks of a storage array
This text, mainly written in the form of a technical terms glossary, is meant as quick-start guide on rack mounted (computer) equipment as commonly found in server-rooms and data-centers. Short paragraphs per term summarize often complex matter to provide you with an overview of the field, a first primer on this fascinating topic. Get a grip on standards, industry terms, common abbreviations, rack dimensions, rack materials and more. Micropolis believes in the advancement of scientific and engineering excellence through support of education, of research and by sharing knowledge. So, let's try that and dive right in.

10-inch rack (10" rack)

While it is common to use one 19" rack unit for two devices side-by-side, dedicated less-wide racks are finding their way into IT deployments in recent years. 10" racks usually are less deep, in comparison to common 19" server cabinets, following the overall smaller footprint. 10-inch rack dimensions are: exactly 10" (254.00mm) from side to side horizontally (front plate), including screwing area. Actual usable width is 8.75" (222.25mm) clear area in-between vertical screwing rails ("rack opening"). Both standards, 10" and 19" use rails of same width, 0.625" (15.875mm). Apart from saving space in commercial installations, 10-inch rack frames are deployed in in military, in airborne or otherwise weight or space constrained scenarios. While dedicated 10-inch switches, 10-inch hubs and 10" computer enclosures are available, it is common in SoHo or business environments to install, not specifically 10", consumer routers or similarly small devices in 10-inch racks in a DIY fashion on 10-inch rack shelfs. Audio devices like microphone receivers, tone generators and effects processors use a 10"-similar half-width rack format, the 9.5" footprint, for decades.

19-inch rack (19" rack)

is a standardized type of technical furniture, a frame or enclosure, of 19" width for mounting multiple electronic equipment modules stacked over another on two parallel vertical rails. The "EIA 19-inch Standard Rack" (EIA-ECA 310E) is very common in scientific and computer / data-center environments. The front plate of one module measures 19 inches (482.60mm) wide, thus the name. The width of the front plate is 19" (482.60mm) in total, including the screw terminal area, with 17.75" (450.85mm) clear area in-between vertical screwing rails (called "rack opening"). One height unit (a "rack unit" ("RU"), measured in "U", 1U, 2U, 3U, etc.) is 1.752" (44.50mm) high. 19" racks may be embodied as open frames, offering essentially vertical screwing rails only ("two-post racks", popular in telco applications) or as open or closed cabinets (usually 24" wide, 609.6mm), with optional additional internal width outside the rail area for more elaborate cabling.

19" rack modules may be short enclosures or very deep ("mounting depth"). Larger mounted enclosures, meaning with often added height and usually very deep, are commonly screwed to the front and rear posts, to properly support the heavy weight. When ball-bearing "Rack-rails" are used as underpinning in this four-post bolting, the whole enclosure can be pulled out like a drawer for easier access. Such a setup is very common in high density data storage servers or disk arrays, where one enclosure may hold over 300 3.5" hard disk drives and max out the weight capacity of the form factor. A complete rack is usually 42U or 48U (height units) tall, with half-height and other form-factors available for space constrained or small office applications. For local IT or audio/IT equipment installations, it is common in back-office environments to have one half or full height rack, self-contained and sometimes sound-proofed, to be operated in lieu of a dedicated server-room.

Visual to-scale comparison between 10" inch rack and 19" rack dimensions
Visual to-scale comparison between 10" and 19" rack dimensions, CC-BY-SA Micropolis, adapted from TomVocke

IEC Norm 60297 racks

The international (based in Switzerland) organization "International Electrotechnical Commission" (IEC, in French "Commission électrotechnique internationale)") has developed a nested series of norms to describe 19" rack mechanical structures and a system of 19" rack and subrack building blocks down to the PCB level - from rack cabinets (level IV) over rack equipment / module carrier chassis (level III) down to modules (level II) and PCBs (level I). IEC 60297 is largely equivalent or compatible to the standards described in EIA-ECA 310.
  • IEC 60297 defines the high level 19" rack "grid system", meant as an envelope or root document for the standards series
  • IEC 60297-3-100 (read 60297 Part 3-100; formerly IEC 60297-1 and IEC 60297-2) describes the basic dimensions of front panels, subracks, chassis, racks and cabinets (Level IV and level III)
  • IEC 60297-3-101 (read 60297 Part 3-101) describes Subracks and associated plug-in units, down to PCB sizes of the "Eurocard" format (level II and level I)
  • ... (omitted here, a number of detailing documents, regarding connector alignment, shielding, etc.)
  • IEC 60297-3-108 defines standards for "R-type" (ruggedized) subracks and plug-in units, i.e. ruggedized variants of the mechanical structures defined in 60297-3-100, but for heavy weight and large form factor, for large volume applications, e.g. cloud-computing servers, telecom servers
  • IEC 60297-3-107 similar to Part 3-108, but for Small form factor and light weight, for large volume applications, e.g. embedded systems, mobile/ubiquitous computing systems

23-inch rack

The 23" rack is a wider rack format mostly adopted in the field of US telephony exchange infrastructure, sometimes referred to as the "Western Electric standard" due to mostly Western Electric using it. Hole spacing varies and only in some cases matches the 19" norm.

2-Post Rack

also Telco rack (short for "telecommunications rack")

3-Phase power

as of 2024, the use of 3-Phase power is on the rise in data-centers and server-rooms as it reduces the number of circuits required, optimizes power load balancing and allows a greater flow of power into individual racks.

4-Post Rack

Simpler racks are built with a frame of two vertical posts, the rack side rails. With heavier equipment, the front-only screwing mount might exert an excessive force to the front plate and a mounted enclose might bend or break. A 4-Post Rack solves this by offering a second pair of posts on the rear side of the rack enclosure as "Structural support". Bolting equipment to the front and the backside offers sufficient support for even the heaviest of equipment. Apart from additional mounting options, a 4-Post Rack is naturally also the base of most Rack Cabinets, speaking of a "4-Post Rack" with open constructions and an "Enclosed Rack" with side-paneled or closed constructions.

500 Series

the "500 series" is a form-factor specification for audio/signal-processing equipment and carrier Subracks, defined by Automated Processes, Inc. (API) during the 1970s. It is sometimes abbreviated as "API 500", stemming from an early EQ cassette sold and manufactured by API, the "API 550". The 500 series format was recently formally standardized and opened by API through their "VPR-Alliance". 500 series shelfes/ cabinets are usually named "housings" or a "lunchbox" (which is an API trade-mark), the latter emphasizing the fact that many users carry their setup of 500 series components (their "custom signal chain") with them on mobile recording situations or to music gigs. Each 500 series module (cassette) is 3U high and 1U wide and connects to a common power and i/o backplane installed on the rear of the rack. Many racks feature on-board PSUs, occupying 0.5 to three of the horizontal rack positions. With a full 19" enclosure offering space for 10 vertically inserted and horizontally organized cassettes (plus a little space left), an onboard PSU usually reduces empty slots to 8. Some 500 series cabinets allow cassettes to be inserted/installed horizontally, 3U high, so that when a "lunch box"-style enclosure is carried or placed vertically (19" perspective: "on the side"), with a handle on one side (then "the top"), the individual cassettes can be accessed and used in their intended upright orientation. API also offers modules for a "200 Series", featuring less tall 1:2 ratioed vertical modules and matching carrier chassis, with 12 slots (and a little) in a 2U 19" rack module.

AC adapter

also known as "External Power Supply", "AC/DC adapter", "Wall charger", "Power adapter", "Power brick" or colloquially "Wall wart". An AC Adapter is a small kind of power supply and commonly the consumer or smaller version of a (more industrial, more enterprise-y) Power Supply Unit (PSU). AC adapters usually either come in the form of a corded rectangular box ("power brick") or as a case resembling a larger AC plug ("wall wart").
Different AC adapters (wall warts), EU and US plugs, and a brick-like laptop power supply
Different external power supplies as common for smaller consumer-grade devices. Tone-generators ("expanders", in music production), half-rack audio equipment and some shelf-based 10-inch rack components also often use these "wall warts".

Airflow & Cooling

Aluminum priming

Aluminum (BE: "Aluminium"), as it is not containing iron, is a non-ferrous metal with many desirable properties but also the undesirable property of building an aluminum oxide layer on the very surface, by itself and quite quickly. And while this natural process is good in protecting the aluminum against environmental influences, it is also the reason why aluminum is relatively difficult to paint or coat. Enamel and acryllic varnishes will simply not adhere ("stick") to untreated aluminum and paint is destined to come off in places. Mechanical aluminum preprocessing, like sanding or washing, even just before painting, won't perfectly remove the oxidized layer. Thus, in painting or coating aluminum, a specialized primer solution has to be applied, sprayed or painted, in order to allow the varnish to build a firm bond with the metal.


Anodizing is a surface finishing process for metals. Anodizing is one form of surface passivation and part of a number of processes of intended anodic surface oxidation. Different techniques of surface anodization exist, with an electrolytic passivation process sometimes known as "Eloxadizing" (a German word creation) being the most popular. The Eloxal anodizing treatment actually transforms the uppermost surface of an object by growing an oxide layer, usually to the same amount "into" the surface as it "grows" to the outside. This actual transformation of the surface is different from galvanic processes where a different material (usually zinc) is laid (applied) onto the metal surface. Anodizing is a measure to prevent rusting (corrosion). It is possible (and popular) to create colored anodized aluminium.

ATA road case rack

The abbreviation "ATA" is short for "Air Transport Association of America" (ATA) the older name of today's "Airlines for America" (A4A), a central organisation for lobbying and standards in the aviation industry. One standard brough forth by ATA was the "Specification 300" dating back to 1960, describing a case that is "Reusable for a minimum of 100 round-trips usually fabricated out of plastic and / or metal" with "(a)ll hardware, including fasteners used to secure a lid closed, shall be recessed, flush or guarded so that no protrusions could cause damage to the container or to other goods shipped in the same conveyance" (Specification 300, 2008, pages 31 and 22). For touring bands and troupes, such cases became the go-to boxing for equipment, and also for readily installed 19" rack based equipment. This is where the term "flight case" came from, or from being on tour, "road case". The common appearance in black wood or plastic with silver aluminum or steel corners became synonymous for a "flight case", even when it doesn't adhere to original ATA specs. For easier handling, ATA compliant rack cases are usually not 42U / full-height tall, but shorter, of around 21U and on caster wheels. Inside, flight case racks are often insulated and shock-proofed, via damping material or spring mechanisms. Cabling from one of those racks to another or to amplifier, speaker or light equipment is usually done via Harting connectors and thick "cable snakes" ("cable assemblies").

Automatic Transfer Switch

sometimes "Auto Transfer Switch", is a feature of Power Distribution Units (PDU) to offer power redundancy on the PDU level. Having a PDU connected to multiple power sources, "ATS" is an in-built mechanism of the Unit to switch from one power source to the other in case of failure of one.

Blanking Panel

Many rack mounts or cabinets offer more space than is occupied by front-facing equipment. In order to tidy up the appearance of a rack, optimize airflow or secure critical cabling, an unspecific simple piece of sheet metal or extruded aluminum can be bolted into free units of the front- or rear-side of a rack. Blanking Panels (also "blanking plate" or "Blank Filler Plate") are sometimes customized with DIY modifications (drilled holes, sawn openings, etc.) to serve specific mounting needs of non-standard sized devices.

Brush Panel

Blanking plates come in many forms, with ventilation openings, with cable ducts, cable management hooks etc. A "brush panel" has a large opening with an inserted horizontal brush curtain, so that cables can be easily run through it and the brush bristles acting as a simple seal around the cabling, helping to control air flow inside a cabinet.

Cage Nut

Cage Screw

What is a cable?

A cable is a collection of wires. While the terms cable and wire are often used interchangeably, there's actually a difference. The wire is the conductive metal part, often copper, aluminum or an alloy, which may be made of a solid extruded piece of metal or multiple strands. A wire doesn't necessarily have to be protected on the outside by a non-conductive material. However, a cable is a collection of wires where each wire is protected (insulated) against contact with the other wires in this cable by some form of non-conductive material, individual thermoplastic sheaths around each wire or by embedding all individual wires in some common insulator material. The collection of wires inside a cable is usually wrapped together by some form of outer cover, made from the same or a different insulator material as used for the internal wires. It is common to have wires and/or cables being wrapped by silicone, rubber, textile meshes, thermoplastics, vinyl, rubber, polyurethane or heat-shrink plastic. With many cables, complex cabling or in combination with movement, cable and wiring systems may need some form of "Cable management".

Cable Arm

Some rack cabinets or rack mount equipment features specially designed "cable arms" as part of cable management. When installed equipment is, for example, placed on rack rails and is later pulled out for maintenance, the multitude of cables routed to a server or storage enclosure might get in the way, get damaged or get pulled out. In order to prevent cables getting stuck or in the way, all cables during setup of a system are placed on specific articulated cable arms, a system of links and joints, bolted to the enclosure or the rack cabinet. When a system is pulled out, the cable arms swings out accordingly, supports the cable and manages them in a predefined way, so a system may continue running uninterrupted or the cabling loom of the installation remains intact.

Cable Classes

Computer networking Patch Cables are divided into several classes, where each class defines the amount of shielding employed and the maximum frequency rating. Electrical ("copper") cables are categorized as:
  • Class A: Up to 100 kHz using Category 1 cable and connectors
  • Class B: Up to 1 MHz using Category 2 cable and connectors
  • Class C: Up to 16 MHz using Category 3 cable and connectors
  • Class D: Up to 100 MHz using Category 5e cable and connectors
  • Class E: Up to 250 MHz using Category 6 cable and connectors
  • Class EA: Up to 500 MHz using Category 6A cable and connectors (Amendments 1 and 2 to ISO/IEC 11801, 2nd Ed.)
  • Class F: Up to 600 MHz using Category 7 cable and connectors
  • Class FA: Up to 1000 MHz using Category 7A cable and connectors (Amendments 1 and 2 to ISO/IEC 11801, 2nd Ed.)
  • Class BCT-B: Up to 1000 MHz using with coaxial cabling for BCT applications. (ISO/IEC 11801-1, Edition 1.0 2017-11)
  • Class I: Up to 2000 MHz using Category 8.1 cable and connectors (ISO/IEC 11801-1, Edition 1.0 2017-11)
  • Class II: Up to 2000 MHz using Category 8.2 cable and connectors (ISO/IEC 11801-1, Edition 1.0 2017-11)
Fiber-Optical cabling is defined in a number of OM ("Optical Multimode") classes defined by respective ISO, TIA/EIA and IEC norms:
  • OM1: Multimode, 62.5 μm core; minimum modal bandwidth of 200 MHz·km at 850 nm (retired)
  • OM2: Multimode, 50 μm core; minimum modal bandwidth of 500 MHz·km at 850 nm (retired)
  • OM3: Multimode, 50 μm core; minimum modal bandwidth of 2000 MHz·km at 850 nm
  • OM4: Multimode, 50 μm core; minimum modal bandwidth of 4700 MHz·km at 850 nm
  • OM5: Multimode, 50 μm core; minimum modal bandwidth of 4700 MHz·km at 850 nm and 2470 MHz·km at 953 nm
  • OS1: Single-mode, maximum attenuation 1 dB/km at 1310 and 1550 nm (retired)
  • OS1a: Single-mode, maximum attenuation 1 dB/km at 1310, 1383, and 1550 nm
  • OS2: Single-mode, maximum attenuation 0.4 dB/km at 1310, 1383, and 1550 nm

What is a Cable harness?

Often when cables are bound or assembled together as part of a thicker bundle of cables, some sort of "Cable management" is used to improve maintainability, operational safety and reduce faults, by preventing wiring failures or people or equipment getting entangled in cables. Some simple form of cable management is pulling individual cables through cable ducts, but during manufacturing, when the same wiring setup is repeated many times, this may lead to wiring faults or unnecessary stress on individual cables. Thus, in the early 20th century, it became popular to bundle cables in ad-hoc bound or pre-assembled cable harnesses. Sometimes different terms are used to describe different types of Cable harnesses ("wire harness", "wiring harness", "cable assembly", "wiring assembly" or "wiring loom").
A "wire harness" is usually the most simple form of a cable assembly. Here, a bundle of usually single core wires (so its probably better to speak of a "wire harness") is assembled into one bundle of wires, each isolated against each other but bundled. Over the years different techniques of cable lacing were used, with rope, with tape, with cable ties, knitting in elaborate patterns. A wire harness usually has each single wire visible.
More elaborate are "Cable assemblies", where a number of cables are combined into one (thicker) sleeve. In contrary to a wire harness, a Cable assembly usually is a bundle of cables, meaning the individual "wires" are actually multicore cables. A cable assembly has all included cables protected by a single outer protective sleeve, giving the appearance of one thicker cable.
A "Cable loom" (sometimes less exact "wiring loom", or "electrical loom") in turn is a bundle of multiple Cable assemblies, wire and combinations thereof into one complex system. Many cable looms have the appearance of wiring harnesses, but each component is a multicore cable or wire connection.
Wire harnesses and Cable looms often are pre-fabricated on dedicated pinboards, where a defined routing layout is used to route wires and cables into a specific pattern, giving the resulting assembly a specific shape, where individual wires or cables may have different length, following defined paths or breaking out from the harness/loom at specified points. After a build, technicians can tests such pre-assembled harnesses/looms by connecting the assembly to test circuits. During installation of such assemblies, having a tailored bundle decreases installation time, prevents mistakes and helps with the standardization of work processes.

Cable Management

Cable management as a general practice is the process or guideline of laying, routing and pulling cables in a tidy and organized way. With moving systems, where cabling is applied outside the moving structure, like with robots or when connected modules move relatively to each other, carefully controlling cable flex improves security and maximizes cable life. Thus, cable carriers for cables and hoses are commonly used on industrial robots or in rack equipment to optimize cable management. From a more general perspective, cable management is an important aspect of mechanical and electrical engineering, inside machines and housings and cabinets. One important technique is to gather a number of cables in "Cable ducts" or assemble multiple cables as part of a "Cable Harness".

Cabling Standard

There are a number of standards regarding data center cabling, giving advice and setting best-practices for (structured) rack cabling, rack to rack cabling, row cabling, and data-center wide / backbone or facility cabling.
  • ISO/IEC 24764
    more specifically "ISO/IEC 24764:2010(E)" specified generic cabling systems for data centers, supporting a wide range of communications services. It covered balanced cabling and optical fibre cabling. It was based upon and referenced the requirements of ISO/IEC 11801 and contained additional requirements that are appropriate to data centres in which the maximum distance over which communications services are distributed does not exceed 2000 meters. This now replaced standard has been revised to form "ISO/IEC 11801-5:2017", incorporating corrigenda and amendments of "ISO/IEC 24764:2010/Amd 1:2014".
  • ANSI/TIA-942
    Telecommunications Industry Association (TIA) ANSI/TIA-942-B (in revision B), officially the "Telecommunications Infrastructure Standard for Data Centers" is an "American National Standard" (ANS) setting minimum requirements for data center infrastructure. It certifies that design documents of compliant equipment have been reviewed for conformity to the design criteria, aligned with a certain "rating level". For facilities, that design documents have been physically onsite inspected and been verified and practices like modularity have been implemented according to the standard an a respective "rating level". These "rating levels" refer to the standard's four rating levels: "Rated-1: Basic Site Infrastructure2, "Rated-2: Redundant Capacity Component Site Infrastructure", "Rated-3: Concurrently Maintainable Site Infrastructure" and "Rated-4: Fault Tolerant Site Infrastructure", the highest level and most redundant type of rating. As of 2024, the standard is again under revision and about to be released as "ANSI/TIA-942-C" (revision C).
  • ANSI/BICSI 002-2014
    is an "American National Standard" (ANS) for Data Center Design and Implementation Best Practices. It is usually regarded as complementing the ANSI/TIA standards, as BICSI publications tend to be more detail-oriented than TIA standards. BICSI as such provides detailed guidelines for the layout of mechanical, electrical or thermal systems of a data center, and taking related topics like security considerations into account.

Cantilever Rack or Shelf

Cantilever is a synonym for a simple beam or statically loadable arm holding a weight. In logistics and storage, Cantilever Racks are open racks with shelving levels made up of horizontal steel beams, usually used to store long goods, like carpet coils, wood packages, sheet metal. In a datacenter context, a cantilever rack or shelf is a type of Rack Shelf with a slanted support structure or side beam, and as any rack shelf can be used to store arbitrary smaller hardware and/or devices. Sometimes an interlock system (grooves or cut-outs on the shelf bottom) is offered to attach smaller sub-assemblies to hold (consumer) devices, for example large numbers of mobile phones, side by side in high density, for Ci/CD ("continuous integration and continuous delivery") applications, where apps or software is tested on many hardware platforms to guarantee compatibility, etc. Cantilever Racks are sometimes customized with DIY modifications to serve specific support needs.

Cold-rolled steel

also known as "Cold-formed steel" (CFS) or "cold worked steel" is any formed steel that is shaped in a processes carried out below recrystallization temperature (of steel). In raw material, like sheet metal, cold-rolled (in difference to "hot-rolled steel") usually describes how the metal was brought into the flat raw (sheet) shape. Shaping or "forming" can mean rolling to reduce thickness (as noted before), but also subsequent processes, like pressing in a press brake, punch press or stamping press, bending (folding) in a brake press or Cornice brake et cetera. Cold-forming usually leads to heightened strength and toughness but as steel in its various mixtures and alloys is graded in many aspects, the more colloquial terminology "cold-rolled steel" is often used as a marketing term to emphasize the robustness or strength of the used material in rack equipment. Cold rolled is one of many features to describe steel types and grades.

Co-Location Cabinet

depending on style often written as "CoLocation Cabinet" in CamelCase, is a type of 19" (computer) rack that features multiple, often three, front doors, offering three isolated racking compartments, with heightened security features, locks and an overall sturdy design, so that data centers offering access to equipment by their tennants can allow access to the data-center floor and a customer's rack without exposing other tennants' equipment to unauthorized access.

Commercial off-the-shelf

abbreviated as "COTS", sometimes varied as "commercially available off-the-shelf" is a term to describe products that are ready-made, don't need preparation or adaption prior to deployment and are usually easily available with short lead times. COTS is the opposite of tailor-made, custom-made, or bespoke solutions. Using a Blanking Panel, drilling and sawing an opening to it to build a DIY router mount would be using an "off-the-shelf" blanking panel to build a custom rack-mounting kit. One well known abbreviation related to COTS is "Mil-COTS", refering to COTS products for use by/ or used by the U.S. military.

Console Drawer

Slide out combination of computer display, keyboard and trackball or mouse, usually designed in the form of a 1U or 2U rack mountable drawer. Most comnsole drawers are single screen but some designs offer multiple displays which slide out horizontally. Datacenter technicians can then stand in front of a rack and operate a console terminal without carrying a separate laptop or other terminal. A console drawer is an on-site local terminal solution (cmp. "Console Server" or "remote management").

Console Server

also known as "console access server", "console management server", "serial concentrator", "serial console server" or "terminal server" is a device that connects to the RS232 serial port of networking (router, PBX), computer (servers) and enclosure management devices (PDUs, Rack management card) and tunnels their serial communication via Network (LAN, TCP/IP, or POTS/ "Plain Old Telephone System") to a remote management terminal ("Serial over IP"). While the more general term is "Terminal Server", in datacenter lingo the more common term is "Console Server" as the terminal server is commonly used only to connect to console ports (COM ports) of connected hosts and tunnel system DevOps sessions via Telnet or SSH ("remote console").

Cornice brake

Simple Cornice brakes are hand operated bending benches for metal forming. A sheet metal blank is placed on a flat bed and affixed by some clamping mechanism, holding it firmly. One part of the formerly flat bench is hinged and can be rotated around so that one flank of the sheet metal is bent. Some Cornice brakes operate circular while others have a more ellipsoid hinging mechanism, compensating for the deformation of the metal during the bend. Modern large computer controlled panel bending machines work similar, but combine the flat feeding mechanism with a computer controlled bending stamp. The difference to a press brake is that a "Cornice brake"-like mechanism doesn't press the metal sheet into a tool but produces the bend by bending the metal against an edge to produce a radius ("swivel bending"). Modern machines are also often embodied as "combination machines", adding the ability to laser cut inserted workpieces.

DCIM (Data Center Infrastructure Management)

Usually software solutions that allow data center operators to log, monitor and control d data centers infrastructure, usually down to the row and rack level. Monitoring security, environmental conditions and metrics like power consumptions allows operators to employ best practices and enforce regulations, for example, for power consumption or energy consumed for climate control.

DIN Rail

is a horizontal metal mounting rail usually used for mounting PLCs (industrial control equipment), relais, motor controlers and circuit breakers. It emerged in Germany, where it was first implemented during the 1920s and later elaborated into an industry standard (German Norm) by "Deutsches Institut für Normung" (DIN). As of 2001, DIN EN 60715 defines four variants, which have since been adopted as international (IEC) standard (IEC/EN 60715). The most well known DIN Rail is the top-hat shaped "Top hat rail", with 35mm wide types available in two depth dimensions and one smaller 15mm wide variant. The 35mm wide variant is known as "TS35 rail" in the USA. The fourth standardized type is a "G"-shaped rail type. A "C"-section rail type sometimes used is not part of the standard. Similarly to 19" rack mounting equipment, modules on a top hat rail are measured in "module widths", usually abbreviated as "M" (or less often "standard units", "SU").


In order to protect metals against corrosion, deep drawn metal parts or whole assemblies can be coated by "dipping" (submerging) the whole structure into a bath of liquid coating solution. When the structure is lifted out of the bath again, a thin layer of the coating material dissolved in the liquid has settled on the surface of the object. In electrophoretic deposition (EPD), part of an overarching category of coating processes known as "chemical solution deposition" (CSD), an electrostatic charge is used to optimize the adhesion of the particles dissolved in the coating liquid - similarly as electrostatic charging is used in powder coating. Dip-coating is very effective to guarantee that a protective film has built on every surface and in every crevice of a structure. The quality and layer-thickness of the applied coat depends on environmental factors like temperature, air pressure and humidity or the motion of the structure inside the bath. In automobile part production, it is common that a whole car body is drawn and rotated through large basins to ensure that the anti-corrosion liquid has reached every little unevenness of the part, such as with small trapped details or on weld seams or weld points. Once the dip coat is applied, the coat is cured in a heat treatment, baking the coat onto the processed surface (stove enamelling). Dip-coating may be part of a multi-step anti-corrosion treatment, where the Dip-coat layer acts as a first ceramic-like protective layer ("dipcoat priming") which is then powder coated in a second step to perfect the surface protection.


Short for Electronic Industries Alliance (EIA). Rack equipment is standardized in document "EIA/ECA-310" for "Cabinets, Racks, Panels, and Associated Equipment". As the EIA ceased operations in 2011, ECA continued her work, and in turn ECA is expected to merge with the National Electronic Distributors Association (NEDA) to form the Electronic Components Industry Association (ECIA).

Electromagnetic compatibility (EMC)

electrical equipment usually produces unwanted electromagnetic energy and EMC labels techniques to mitigate or control the amount of emitted electromagnetic energy or to allow equipment to work inside its defined parameters while being immersed in a specific electromagnetic environment, dimming effects such as "electromagnetic interference" (EMI).

Electromagnetic interference (EMI)

in radio systems or equipment sensible to radio waves, electromagnetic inference (sometimes "radio-frequency interference (RFI)") labels unwanted induction of interference (disturbance) into a system, computer or, more general, any electrical circuit. Various strategies can be employed to mitigate EMI, for example, electrical ducts can be laid out in way so that they are less prone to act like an antenna. In EMI shielding (EMC protection, hardening), the enclosure of equipment is an important element, with choice of material, design, coating of surfaces and sealing playing an integral part.

Enclosed Rack

A type of closed rack cabinet, opposite of an open rack frame, used to better protect mounted devices.

ETSI rack

The ETSI rack (sometimes "21-inch rack") is a standard defined by the European Telecommunications Standards Institute (ETS, in document "ETS 300 119") for rack mounting infrastructure. One difference to common EIA-310 rack is that the ETSI rack is slightly wider, with front-plates measuring 21.1in (535.00mm) wide and a rack opening of 19.68 inches (500.00mm).
ETSI rack vs. EIA-310 rack dimensions
ETSI rack vs. EIA-310 rack dimensions, CC-BY-SA, by Jahoe

ETSI bracket

An ETSI bracket is an adapter used to install EIA-310 (19-inch rack equipment), which is about 2 inches less wide, into the larger rack opening (500mm) of an ETSI standards based rack frame or enclosure. Some ETSI brackets are embodied as "rack ears", screwable to the side of 19" equipment, while other ETSI adapters are build as frames being slid over the smaller 19" devices.

Extruded Aluminum

The process of extrusion (from Latin "extrudere", to expel or drive out) is a mechanical process for metal forming and also plastic forming. It is used to create profiles of a given shape (or cross-section) by pressing a raw block of material through a die (or stencil). In a similar technique to what pastrie chefs use to create "spritz biscuits" (moulded cookies, piped biscuits), here the material is either warmed up or heated and then pressed through a static or rolling forming duct. Although many materials can be extruded (plastics, elastomeres and metals), the process is mostly used for aluminum and aluminum alloys to create shapes and profiles difficult to achieve in other processes. In rack and computer equipment, extruded aluminum is very common, as backbone structures in enclosure designs, corner profiles of boxes and as construction aluminum square bars. It is also used to fabricate heat sinks and other smaller components where an extruded metal profile is cut down to result in a desired part.

Fan tray

In closed rack cabinets, thermal management is crucial. A fan tray is a horizontal, usually 1U or 2U high rack module with horizontally installed cooling fans, covering the whole surface of the module. Installed as part of a rack assembly, a fan tray can help with in-cabinet ventilation or, when installed at the top or bottom, to exhaust hot air, or take cool air in.


is a proprietary coating process and coated sheet steel brand, consiting of 55% aluminum, 43.4% zinc and 1.6% silicone. Galvalume is a registered trademark of BIEC International, Inc. Galvalume is a highly effective anti-corrosion process and a popular material choice in rack equipment.


Galvanization or "galvanizing" is one form of protecting metals against corrosion. The process applies (lays, in a process of "plating") a thin zinc coat onto a metal surface, usually by submerging parts or a whole structure into a bath of molten zinc. This "Hot-dip galvanization" process is similar to Dip-Coating as it allows the zinc to reach every unevenness or crevice of the galvanized workpiece. Galvanization forms a typical pattern, a crystalline surface, on galvanized parts resembling Voronoi cells, where each cell reflects light slightly different. Similarly as ECD in Dip-Coating, an electrolytic charge is commonly used to optimize the particle deposition on a bathed object ("electroplating") in "electro-chemical deposition" (ECD), which is part of an overarching category of coating processes, "chemical solution deposition" (CSD).

Half-rack format

Comparable to 19-inch rack frame enclosures, a half-rack, 10-inch, or 9.5" rack only uses half the width of a standard 19" rack, thus offering a modular mounting option on a smaller footprint.

Hard reset

turning a device off and on again, in order to trigger a reboot or restart. On uptime optimized devices, this is usually the last resort when an otherwise unrecoverable situation arises. Normally, system administrators would prefer a "soft reset", where a system is going to halt/reboot/restart via defined procedures, usually triggered in software from the local or remote shell/console.

Harting Connector

Harting is a multinational manufacturer of electric connectors and the "Han" line and similar connectors made by Harting have become synonymous for multi-pin rectangular macro connectors that are popular in the (live) event, show and audio space to connect flight case racks and subracks via thick Cable assemblies, usually colloquially called "cable snakes" in the audio industry. (Note that a "Subrack" here describes a smaller, trolley type audio 19" rack of around 21U height, not IT Subracks for vertical cards.) The 16 pin Harting connector (dimensions 109.60 x 35.50 mm) is a connector with screwing terminals inside the rectangular outer shape. Other Hartings come in 48x35mm, 65x35mm, 82x35mm, 86x71mm or 108x35mm and have screwing outside the cutout rectangle of the connector. The large Harting connectors are usually rated for multi amp power applications, as needed for dimmers and connected lights. As part of cable managment, it is common to guide the thick cabling, in ducts etc. through a "Harting trumpet", a funnel-shaped (cone) hole protector that is intended to prevent wear and abrasion on the cable.

High Density

Home mounts

Not really a term from the enterprise or datacenter rack world, yet it describes mounting solutions for the Small or Home Office (SoHo) environment, offering to streamline cable management, put away with tangled cable nests and to upgrade computer setups through clever wall, deskside or under-desk fasteners.


common abbreviation for "horizontal pitch", the unit of measure for horizontally laid out front-plates/components in 10" or 19" Subrack rack positions. More on vertical cards usually mounted side by side under (cmp.) "Subrack".

In-Cabinet Rack

With edge installations, branch networks or smaller IT deployments, it is common that computer hardware is installed in a (sometimes customer-facing) standard office environment. In order to hide the technical hardware and achieve a less industrial appearance, it is common to have 19" racks installed inside wooden furniture cabinets. Some racks are especially designed for this practice and feature special bolting options, slide or swivel out mechanisms and other ergonomic features to allow technicians easy access to cabling and equipment.


Some enclosures feature pre-cut holes where the cut is done as a perforation of the enclosure's material, either sheet metal or (abs) plastic. A knockout can then be pushed through with manual force only when a cable duct or hole is needed.

KVM Mount

Maintenance Bypass (MBP, MAINS mode)

also known as "Service Bypass" is a fault-tolerance and servicing feature of some Power Distribution Units (PDUs). Without shutting down the equipment, the power can be switched away from the UPS when it needs to be replaced. It is common to serially link the main power to a UPS first and then feed UPS -backed power to a PDU. In case the UPS in this setup fails, it wouldn't be possible to replace the UPS without interrrupting power to the PDU and with it to connected rack devices. For this scenario, some PDUs have an additional power inlet where mains power can be connected so that connected equipment can draw input power from the MBP through a dedicated power inlet.

Lace Bar

part of wire management (cable management), a "lace bar" is a vertical or horizontal support element, that helps to route and support in-rack cabling.

Laser cutting

Laser sheet metal cutting is a common technique in manufacturing shaped workpieces from raw sheet metal blanks. Laser cutting belongs to a category of techniques to cut material with heat, like flame cutting or plasma machining. It is slower than cutting metal pieces from sheets in stamping presses but more flexible with less tooling required and more flexibility. Apart from flat sheet metal laser cutting, there are dedicated machines for laser pipe cutting. Today, laser cutting machines are often embodied as "combination machines" where a laser turret is able to cut arbitrary shapes from a metal sheet and an attached bending mechanism, either a press brake or cornice folding mechanism, is able to bend workpieces according to computer controlled shapes. Laser cutting is an alternative to (cmp.) "water jet cutting". The groove created by a laser cut ("kerf") is very thin, usually thinner than with waterjet, yet with laser cutting there's a thermal impact on the cut material and may change the material's structure near the kerf.

Metal forming

To produce workpieces of high strength and precision, metal is one of the best materials available. In metal forming processes, metal can be brought into many shapes, by pressing it through a die in extrusion, or applying a forming force, as is done in metal presses or metal bending machines. Blanks of thin sheet metal blanks can be formed by being bent on bending machines, either folded (flanged) or clamped (in a press brake). Stamping presses are (usually) large format hydraulic or servo driven steel presses (or other metals) where a die is used to deform, indent or cut flat metal blanks ("hard tool stamping"). Punching machines work on sheet metal and punch holes into metal blanks, like a cookie cutter.

Monitor Mount

With many systems in one rack, it's common to have multiple machines share one keyboard and one monitor via switching hardware. Many monitor and/or keyboard mounts are embodied as drawers, so when an operator works in front of the rack, it can be easily slid out, or stowed away when not in use.


NCT is the abbreviation for "numeric controlled turret" or "number controlled turret" or "CNC turret punching machines". While the more general category of turret punch Presses/ punching machines may also be manually operated, a "numerically controlled turret" are automatic and computer controlled machines similar to CNC machines, where the stamping tool is guided by computer input. "NCT piercing" describes stamping an arbitrary form or shape into or through sheet metal blanks. "NC stamping" is usually regarded as an alternative (more flexible, more economical) to large format stamping presses, as the latter require more preparation, a tooling investment, where a die needs to be machined etc. On the contrary, an NCT machine isn't able to perform all forming techniques and is slower and less strong. The difference between a NCT machine and a machine stamping press is similar to that of a typewriter or an inkjet printer vs. an (offset) printing press.

Notching machine

a notching machine is a simpler (usually manually operated) type of Punching machine and used to form metal. A hydraulic, pneumatic or manually operated turret with a stroking tool is used to "nibble" notches ("corner notching machine") or arbitrary shapes away from the edge of inserted sheet metal. Some machines are able to bend or deform blanks in such a way that a seamless (no weling required) corner cavity of a sheet metal pan is created ("corner former") - a simple form of forging.

Nut Tool

Open Compute Project

A collaboratively industry workgroup initiated by Facebook to redesign major components of datacenter infrastructure, with the aim to increase efficiency, reduce costs and improve overall management of basic datacenter building blocks. Some central topics are cooling and power distribution, physical arrangement of systems in redesigned Server Racks and reusable server blade enclosure design.

Open Frame Rack

Open Rack

(as designed by the OCP)


as a chemical process usually means the intended coating (some metals form spontaneous surface oxidization) of a (metal) surface in order to mitigate corrosion, from oxidization or other reations with the environment. Sheet metal, as frequently used in rack applications, is usually passivized in one form or another. One simple way of passiviation is painting. Aluminum is either processed through chromate conversion coating or anodized. Copper or silver is often gold plated or zinc-nickel plated to prevent corrosion.

Patch Cable

a form of shorter cable (usually around 5-20 inches, 10-60cm) used to connect electronic, opto-electronic or optical devices with each other. A patch cable is sometimes known as "patch lead", "patch cord". It is common to have colored patch cables to color-code their use and prevent cabling faults during installation or maintenance.

Patch Cables in Audio, Music and Sound Recording

Patch cables in audio technology are usually wires with either two or three wires and a cylindrically-shaped "phone connector on either end. Patch cables with two wires use "TS" (Tip Sleeve) connectors with "two conductive rings", and cables with three wires "TRS" (Tip Ring Sleeve) plugs ("TRS phone connector") having "three metallic rings". Such patch cables were common in telephone switchboards of the POTS (plain old telephone system), jack fields (patch fields) where operators were able to patch phone connections/conversations physically together. The name stuck. Today, patch cables are common in the audio recording field where rack-based "patch bays" are used to route audio signals from one device to another, in a flexible way. For example to route a select set of tone generators to a limited number of recording inputs. With modular synthesizers, patch cables are used to "patch" individual components of the tone-generation path together. When routing audio signals, usually three-wire patch cables are used to transmit a "balanced" mono audio signal. "Balanced audio" is less susceptible to external noise caused by electromagnetic interference on longer cables. Although patch cables are short, they usually are part of a longer cable path and with the patch cable being one segment of this path, requires patch cabling to be three-wired as well.

Patch Cables in Computer Networking

Depending on what technology is employed, in computer networking a patch cable may refer to cable with either an optical or electrical inner technology. Fiber-optic cables use one or more optical fibers to carry light. Electrical cables use an inner core of one or more conductive wires made of copper or another cunductive alloy with a link impedance of 100 Ω, usually multiple twisted-pair copper interconnects. Network patch cables today use shielded or unshielded (ISO/IEC 11801) Cat5 ("Category 5"), Cat5e, Cat6, Cat6a, and as of 2024, increasingly Cat 7/7a and Cat 8/8.1/8.2 cables for high speed networking. Cables are terminated using 8P8C (RJ-45) modular connectors with straight-through T568A or T568B wiring.

Patch cables in TV and Video

the SMTPE (The Society of Motion Picture and Television Engineers) standardized "Serial digital interface" (SDI) is a technology for sending video signals over coaxial cables. SDI and HD-SDI use coaxial cables terminated with BNC connectors and are commonly connected via Coaxial or BNC patch bays.

Patching in fiber optics

In fiber-optic networking and communication, jack fields or patch fields are usually called "Splice Box" or "Splice Drawer" and are part of "fiber management" (the equivalent of cable management, just for fiber-optic cables). A splice drawer is used to accommodate and protect fiber splices and their characteristic short loops in 1U or 2u height. Very often, these splice compartments are embodied as drawers, as, in contrary to electrical patch jacks, fiber optic splices must be laid flat and twist-free inside such a drawer.

PC Rack Mount

In corporate IT deployments, oftentimes off-the-shelf PC systems are used as (cheaper) building blocks of computer infrastructure. It is common in web hosting, computer cluster research or small (or SoHO) creative studios to use "generic beige boxes" on Rack Shelf in a High Density setup. Some tower workstation PCs are designed to fit horizontally into the rack opening of a standard EIA rack, and can be screwed in with the addition of Rack Ears. Some PCs are designed to fit side by side into a rack's opening, in groups of two, three or four machines, in 2U or 3U of vertical space. The Cobalt Cube server appliance sold during the 1990s was popularly stored this way.

Micropolis at one point offered the Raidion family of desk-side storage towers. The 3.5-inch drive version Raidion LS included the option to store the usually vertically laid out tower on-the-side horizontally in a server rack with the help of a shelf and mounting brackets, offering customers to move the appliance into a datacenter.

PDU (Power Distribution Unit)

is a multi-outlet power strip device, designed to distribute power to multiple devices (within a rack, "Rack PDU") from a single power source, where the power source might be the utility grid, a UPS or a generator. In the field of audio, a PDU is sometimes called a "rack rider" as it is common to install the PDU on top of audio racks, with utility lighting for devices below and power regulation built-in, to protect rack equipment from power surges, etc. In computer datacenter applications, PDUs are sophisticated pieces of hardware, enabled to not only distribute power but also power-cycle connected equipment, meter power draw, measure room temperature and humidity and transmit such metrics to remote logging and monitoring equipment (cmp. "DCIM"). Power capacities of PDUs are usually rates in amperage. PDUs are available in standard horizontal rackmount designs of 1U or 2U and often optional vertical installation (of 0U, "zero U", "ZeroU"). While all PDUs provide basic power distribution, some models allow local or remote monitoring, on the PDU unit level or down to PDU outlet level, with outlets being metered, switched and metered or the whole PDU ("Smart PDU", "intelligent PDU", "iPDU"). Power redundancy on the PDU level might be implemented via ATS (Automatic Transfer Switch), where the PDU uses multiple power sources and switches from one to the other in case of failure of one (power failover). PDU come in localized for, with output receptacles suitable for the region of the connected devices. Some PDUs offer "Maintenance Bypass" (MBP). Some PDUs offer "Branch Circuit Protection" with a given group of outlets having their own fuse and/or circuit breaker. Some PDUs support the use of "3-Phase power", with phase indicators on PDU outlets.
Power Distribution Unit (PDU) cabling options: using height units, 1U or 2U; or vertical zero U layout along the side, saving rack space
Power Distribution Unit (PDU) cabling options. On the left: a PSU occupying height units, 1U or 2U; on the right: PDU in vertical "Zero U" layout, along the side, saving rack space.

Portable Rack

Powder coating

aluminum, steel or more general metals are all prone to changing their surface in oxidation processes (corrosion), a generally undesirable effect that can be mitigated by applying a protective surface coat. Despite good adhesive properties of standard acryllic or enamel based varnishes, these lacquers often simply do not meet the requirements for durability and strength. Powder coating is a special type of (color) coating where the varnish, before application, isn't a solvent based liquid but a dry powder. This powder, either epoxy or polyester resin based, is applied with a powder gun and made to stick to the powdered object by an electrostatic charge. The powder coat is then cured by heating / baking the powdered object (the powder is "thermoset", "stove enamelling"). During the setting process of the coat, the coat forms a high-strength bond with the coated surface and builds up a scratch and impact resistant plastic surface on top, where the polymer chains have cross-linked with each other. Some newer powder coats can be cured by exposition to UV light, making the overall process less heat-intensive, allowing plastic objects to be powder coated. Powder coating may be one stage of coating, for example after a first step of dipcoat priming or before a finishing overpaint. Powder coats are available in various colors and types, with powders either creating a matte, textured or "rough" surface or cure to a shiny high-gloss finish. Computers, data center infrastructure and rack components are very commonly powder coated in matte or satin-matte coats of a black (RAL 9005), (light) grey (RAL 7035) or white color.

Power Cable Plugs

Different power cord plugs, IEC 60320: C7, C13, C14, C19, C20
Different power cable plugs, according to norm IEC 60320: C7 female plug, as found on smaller A/V or IT equipment (SFF PCs, game consoles, etc.); C13 female plug and C14 male inlet socket often found on rack servers, networking equipment and other computer equipment; C19 female plug and C20 male socket are usually used as mains power couplers on PDUs and other power distribution equipment.

Power Whip (Whip/AC)

power cable assembly used to connect a data center rack to a the data center's or building's facility power busway / main power feed. These "whips" are used as an adapter, as different combinations of rack hardware use different types of connectors. Often a whole rack (via it's PDUs) or a rack's power shelf uses one type of connector, leading into a cable assembly with again a different type of connector, like a more universal AC plug. With an adapter to plug into 208V (30A/50A), 400V (32A) or 415V (30A) power outlets, a rack or parts of it can then, with such a "whip", be connected to a facility's mains power.

Power-Up Sequencing

feature of some PDU models, offering the ability to switch individual receptacles on, one after another, when the whole PDU is connected to power or switched on. This allows power to be be fed in sequence to connected devices, controlling the maximum amount of current flowing while systems power-on and boot or reboot, a situation where many systems draw higher currents than under normal load. Such a scheme is similar to what is known as Staged Spin-Up in data storage enclosures, where storage devices similarly are not spun-up all at once, to control "inrush current" - only here applied to a whole rack of devices and/or systems.

Press brake

A press brake resembles a stamping press as it is usually also embodied as a large H-frame assembly, with an upper element acting as a hammer and a lower element as an anvil. Inserted metal blanks, usually sheet metal, are bent "by delivering an accurate vertical force in a confined longitudinal area" (cited from the ASM tome on Press Brakes, see links at the end of this text). Press brakes are feedback-loop controlled and very accurate, driven either by mechanical, hydraulic or electro-hydraulic drives. The upper tool exerts a downward force into a V- or similarly shaped lower die to deform the workpiece. As the upper tool usually resembles a linear bar, the resulting bend is a straight line. When a worker or some computer controlled mechanism inserts the metal blank, dynamically positioned limit stops (backgauges) help position the sheet and control the length of the resulting flank. The top tools is usually easily exchangeable for specific bends. Computer controlled machines with automated feeder mechanisms are also often embodied as "combination machines", adding the ability to laser cut inserted workpieces.

Press brake manufacturers

PSU (Power Supply Unit)

a PSU converts mains AC line voltage into low-voltage regulated DC power, often provided in a number of low voltages at high currents, as required for the internal components of a computer. Early low voltage devices usually used linear power supplies, which use a rather large step-down transformer as a first step, where high voltage AC is converted into low voltage alternating current. A second step, a linear regulator implemented mainly with transistors then converts AC to DC. The drawback of this design is that a large portion of the converted power is dissipated as waste heat. During the 1970s and 1980s a new design emerged, made possible through advances in producing cheap transistors and control ICs, the "switching power supply". While a linear PSU also switches power, in sync with mains frequency, usually 50 or 60 times per second, a switching power supply switches several thousand times per second. In a switching PSU the incoming AC power is first converted to high-power DC power and then, similarly as in PWM, switched on and off to control the flow of power, resulting in a defined output power based on how long individual on-phases are. This scheme generates nearly no waste heat and switching PSUs may operate at 80-90% efficiency in practive, while a perfect design in theory should be able to achieve 100%. One side-effect of the switching mode is that it introduces high-frequency ripple ("noise") into circuits, requiring additional circuitry to filter out, while simple linear PSUs supply noise-free stable power. Today, computers and electronic devices usually use switch-mode PSUs. Many models also provide stand-by power, allowing a connected system to power down into suspended, "sleeping" hibernation modes, where software defined triggers are able to wake the system up, like "wake-on-LAN", "Wake-on-ring", BIOS or software-set timers or via Human-Interface-Devices (HID), "Keyboard Power ON" (KBPO).

Punching machine

Punching machines (mostly "Turret punch presses") work similar as much larger Stamping presses, as they use a flat bed to affix a sheet of metal and a (usually) overhead "stamp" that is driven vertically into the underlying metal surface to apply dents or cuts in the shape of the stamp ("ram" or "slide"), sometimes with a die below the stamped metal, working in tandem. Punching machines in general may be manually operated or automatic. The process of moving a sheet metal blank into the machine and maneuvering it around on the bed, below the stamping area, is usually servo and computer controlled on today's machines, known as NCT presses. These machines are able to punch, deform, nibble, trim, shear, flare and flange the raw blank at a high pace. The turret is usually able to automatically exchange tools, sometimes in-sync with a die located on the underside of the punching bed. Wheel tools can be used to create rolling offsets and are a quick alternative to usually slower nibble forming operations. Some machine turrets are able to exchange complicated tools, like drilling mechanisms to cut screw threads. Modern machines are also often embodied as "combination machines", adding the ability to laser cut inserted workpieces.

Punching machine manufacturers (NCT)

Rack Adapters

Rack Box

Rack Converters

Rack Drawer

Rack ears

Equipment manufactured to be compatible with 19 inch (or 10 inch rack) form factors sometimes is shipped without the face-plate overhang to screw it into a rack. Such device enclosures are then designed as simple metal boxes with screw threads or drill holes on the side, so that additional "rack ears", or "rack mounting flanges" can be installed if required. The rack ears option is usually chosen by device manufacturers when equipment is expected to be used primarily in "desktop mode", but may just as well be installed in a 19" rack. This configuration is common for audio devices, like tone generators, effects processors, etc. In A/V environments, a side-by-side mounting of two devices plus rack ears is an equally common setup. While most 19" rack ears are fitted to equipment that perfectly fills the rack opening of 19" racks, some narrower equipment might use special wider rack ears, acting as spacers to bridge the gap between the equipment side and the screwing strips of a 19" rack - for example when certain 500 Series audio housings are rack mounted.
Schematic view of 19 inch rack ears
Schematic view of 19 inch rack ears

Rack Handles

in data-center lingo, the term "rack handle" usually refers to the dor handle of rack cabinets. For security, many handles feature some kind of lock, ranging from simple key locks or padlocks to more sophisticated lock types, with smartcard readers, keycode field or wireless access mechanisms. In combination with mechanical door sensors, IR door sensors or other means of intrusion detection, rack handles are an obvious but effective way of implementing high-security or elevated physical security awareness for IT equipment.

Rack Hole Type

There are two types of rack holes in the vertical side rails of 10" and 19" racks, 12-24 Threaded holes and Square holes.

Rack mounting depth

There's no formal standardization for the depth of 19 inch racks ("mounting depth"), probably due to their emergence from open frame structures with only two screwing posts.

Rack Power Strips

Rack Rails

(also "slides" or "rack slides", sold as "rack rail kits")

Rack Shelf

Simple horizontal support, made of sheet metal. A usually three sided, folded structure with screwing terminals and an opening on the front, able to support arbitrary equipment inside the rack opening of a standard rack.
Typical generic 19-inch Rack Shelf
Typical generic 19-inch Rack Shelf (cantilever rack shelf)

Rack to Tower mounts

(Convert rack servers to tower servers, rack workstations to desk-side tower workstations)

Relay Rack

sometimes "2-post relay rack" or colloquially "post relay" is a type of rack with two free-standing vertical screwing strips. The name originated in TelCo installations, where it was common to install telephone sub-station relay banks into this type of rack.

Remote Management

Generic term to describe the (optional) feature of equipment or systems to be controlled remotely, from an off-site terminal or console.

Remote Power Management

ability of equipment, mostly PDUs, to switch power on a given receptacle in order to remotely power cycle servers or devices, to trigger remote reboots or recover from situations requiring a "hard reset".

Single Inlet Device

or a single-corded device is a kind of device that is not designed to have redundant power supplies and comes with only one cord - common with entry-level, consumer, pro-sumer or legacy computer and network equipment. A Power Distribution Unit (PDU) with Automatic Transfer Switch (ATS) redundancy features can be used to mitigate this weakness and enhance the uptime and robustness of single inlet devices.

Secure Racks

Intrusion and tamper proof racks or cabinets.

Secure Server Brackets

Server Bezel

Many hardware vendors distinguish themselves by having branded and styled server front-plates, combining functionality and design. Usually different modules from the same product-family share a common design language so that a filled rack (say, a combination of compute and storage nodes) has one unified design appearance. Sometimes, custom designed racks or rack doors are used, specifically in high value, cutting-edge installations or in high performance computing (HPC).

Stamping press

Stamping presses are (usually) large format hydraulic or servo driven steel/ aluminum (metal) presses where a die is used to deform, indent or cut flat blanks ("hard tool stamping", "deep drawing", "punch drawing"). The basic principle is that of hammer and anvil, with one element, the upper, called "slide" or "ram", acting as the hammer. The counter element, usually static, is the "anvil", a flat bed called the "bolster plate", and is used to fixate the "die", the form the upper ram is driven into to deform the sheet metal blank inserted in between. Stamping presses are able to deform surprisingly thick raw material, so not only sheet metal can be deformed, but also solid metal blocks can be stamepd into shape, for example to mold a frying pan.

Metal stamping press manufacturers

Steel types and grades

Sometimes inaccurately described as "metal", steel is actually an alloy. Alloys are a mixture of materials, a mixture of chemical elements - and to be described as an alloy, one of the elements of this mixture has to be a metal. Alloys are formed to change the characteristics (properties) of the raw material, for example in terms of strength. Steel is an alloy (mixture) of iron and carbon. When an improved resistance towards oxidation (rust/ corrosion) is wanted, chromium is added to the alloy to form stainless steel.

When speaking of steel, around the world a number of standardization schemes (grading systems) have been established to describe the different mixtures of steel (alloys). In the U.S., the standards organization "SAE International" established the "SAE designation system", sometimes also "AISI numbering" as the "American Iron and Steel Institute" (AISI) was involved in the development of the scheme. In Japan the "JIS" steel grade standards are used. In the United Kingdom the "BS" (for "British Standards" as produced by the BSI group) designation is common. In France, the "Association Française de Normalisation" (AFNOR) has set a similar numbering scheme. In Germany there are DIN steel grades, developed by the "Deutsches Institut für Normung e.V." (DIN) and a popular "Werkstoffnummer" (material no.), a 5 digit number. In Europe, generally, there are now efforts underway to replace many more European steel grade standards with a unified "EN" (European Norm) issued by the "Comité Européen de Normalisation" (CEN). While steel grade labels are nationally different, the actual mixtures are often very similar and lookup tables can be used to translate from one designation to another.

SAE steel grade numbering system

In describing the various common steel alloys, there are a number of nested "categories" of steel. The most general two types of steels are pure "Carbon steel" variants and the mixed "Alloy steels". In SAE designation Carbon steels all start with a "1". Alloy steels in SAE designation are numbered with a "2", "3", to "9" prefix, with "Manganese steels" being an exception, as it also is prefixed with a "1", from being "close" to Carbon steels.

Type SAE designation Type and composition
Carbon steels
Carbon steels 10xx Plain carbon, Mn 1.00% max
11xx Resulfurized free machining
12xx Resulfurized/rephosphorized free machining
15xx Plain carbon, Mn 1.00-1.65%
Alloy steels
Manganese steels 13xx Mn 1.75%
Nickel steels 23xx Ni 3.50%
25xx Ni 5.00%
Nickel-chromium steels 31xx Ni 1.25%, Cr 0.65-0.80%
32xx Ni 1.75%, Cr 1.07%
33xx Ni 3.50%, Cr 1.50-1.57%
34xx Ni 3.00%, Cr 0.77%
Molybdenum steels 40xx Mo 0.20-0.25%
44xx Mo 0.40-0.52%
Chromium-molybdenum steels 41xx Cr 0.50-0.95%, Mo 0.12-0.30%
Nickel-chromium-molybdenum steels 43xx Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%.
47xx Ni 1.05%, Cr 0.45%, Mo 0.20-0.35%
Nickel-molybdenum steels 46xx Ni 0.85-1.82%, Mo 0.20-0.25%
48xx Ni 3.50%, Mo 0.25%
Chromium steels 50xx Cr 0.27-0.65%
51xx Cr 0.80-1.05%
50xxx Cr 0.50%, C 1.00% min
51xxx Cr 1.02%, C 1.00% min
52xxx Cr 1.45%, C 1.00% min
Chromium-vanadium steels 61xx Cr 0.60-0.95%, V 0.10-0.015%
Tungsten-chromium steels 72xx W 1.75%, Cr 0.75%
Nickel-chromium-molybdenum steels 81xx Ni 0.30%, Cr 0.40%, Mo 0.12%
86xx Ni 0.55%, Cr 0.50%, Mo 0.20%
87xx Ni 0.55%, Cr 0.50%, Mo 0.25%
88xx Ni 0.55%, Cr 0.50%, Mo 0.35%
Silicon-manganese steels 92xx Si 1.40-2.00%, Mn 0.65-0.85%, Cr 0-0.65%
Nickel-chromium-molybdenum steels 93xx Ni 3.25%, Cr 1.20%, Mo 0.12%
94xx Ni 0.45%, Cr 0.40%, Mo 0.12%
97xx Ni 0.55%, Cr 0.20%, Mo 0.20%
98xx Ni 1.00%, Cr 0.80%, Mo 0.25%

Common steel grades (types of steel)

  • DC01
    DC01 steel is a European cold-rolled steel with a yield strength of around 280 MPa and a tensile strength of in between 390-540 MPa. Other labels for DC01 are "DIN EN 10130", "St12" or "Werkstoffnummer 1.0330". It is a low-carbon steel product, coming on coils ("colts") of flat steel. DC01 is designed for cold forming applications. The "C" in its designation is for (cmp.) "cold-rolled", a manufacturing process. DC01 is a very common material for large metal stamping processes, as in producing autobody parts or in punch drawing (deep drawing). Rougly equivalent steels from other standards: SAE: SAE1008, SAE1010; DIN: FeP01, St12; JIS: SPCC; China: GB 08, GB 08F; India: O; ISO: Cr01, CR22.
  • S235JR
    S235JR, with the prefix "S" meaning "structural steel", is a European hot-rolled non-alloy (carbon) steel of moderate strength, where "235" is giving the minimum yield strength in MPa. Nominal tensile strength is in between 320-490 MPa. Other labels are "DIN EN 10025-2", "St37", "Werkstoffnummer 1.0038". The "JR" designates a specific impact resistance class. S235JR is a common raw material for cold forming applications, like in a brake press. Rougly equivalent steels from other standards: SAE: 1015, A283C (ASTM Grade C), SSGrade33; DIN: St37; JIS: SM400A, SS400; China: GB Q235A, GB Q235B, GB Q235D; India: IS226; ISO: E235B, Fe360B


Special enclosures to accept horizontally arranged subcomponents are called "Subracks" ("sub-racks"), "card cages", "Chassis cases", "rack mount chassis". Subracks employ a horizontal scheme for smaller components which are laid out horizontally inside 3U or taller 19" rack positions, defining a "smaller element standard" inside common 19-inch racks, where larger equipment is in contrary usually laid out vertically, above each other. Horizontally organized Subracks are popular in telecommunications, railway applications, industrial control cabinets and similar industrial or scientific applications. A common form-factor for Subracks is 3U and 6U height as vertically inserted "cards" usually require a certain height. Such cards, usually Eurocard (Euro board, German "Europakarte"), COMExpress cards, Single Board Computers (SBC), fiber networking cards, expansion cards for i/o or networking, are then either screwed in such Subracks or locked in place via a special clamping mechanism (for easier maintenance). Sometimes, Subracks feature connector backplanes so that inserted components (cards) with edge-connectors can act as elements of a system or computer, being connected via an internal bus, similar to ISA bus, or Europe Card Bus, S-100 bus. The unit of width measure for horizontally laid out front-plates/ components/ cards in a Subrack is "horizontal pitch", abbreviated as "HP" ("TE", "Teileinheiten" in German).

Probably the most popular layout in subracks is IEC 60297 Part 3-101 ("Subracks and associated plug-in units") or the "Eurocard format". The standard divides the net rack opening of a standard 19" rack into 84HP (84TE), where each vertical slot is 5.08mm (0.2 or 1/5 inch) wide. This layout is based on the Eurocard PCB format, measuring 100x100mm at minimum, 100x160mm (1.6mm PCB board thickness) being a common size and may increment in 60mm steps up to 400mm depth. One of these 100mm tall PCBs fits into a vertical slot of 133.35mm, adding about 30mm of "wiggle room" for mounting and connectors. Front plates are usually a little less tall, with 130mm being common. Eurocard subracks are often 6U tall while the standard defines 3U, 6U and 9U enclosures ("Baugruppenträger"). When a vertical card is double height, the 33.35mm of "wiggle room" are added once, making a double-tall Eurocard 233.35mm in height with a 267mm (10.5in) tall (266.7mm) front plate. A 9U card adds the 33.35mm height twice, making it a 366.70mm tall PCB inside a 400.50mm tall slot.

Subracks in audio

Aside from industrial applications, Subracks saw increasing popularity in audio and music production since the 1970s, where modular synthesizers, tone generators, compressors and audio fx processors are sold and assembled in 19" Subracks, in smaller modules of varying U height, but less wide.
  • Early synthesizer manufacturer Moog divided the horizontal space into units of 2.125" width, "Moog units", "MU", allowing eight modules to be placed side-by-side into a standard 19" rack opening. Later synth manufacturers, like Synthesizers.com, adopted the format for their products and established the aka label "DotCom format" for these modules. The "Moog Units" format is part of the category of "5U format" modules, all sharing a height of 5 standard rack units.
  • In the late 1990s, US synthesizer manufacturer Synthesis Technology introduced a slightly modified subrack format called "MOTM" ("Module of the Month"), where each "card" is five rack units tall (5U) and as wide as one rack unit (1U) would measure in height, 1.75" or 44.50mm, allowing 10 modules to be placed side-by-side. For these modules, it is common to have double-wide rack cabinets where 20 or 22 modules can be installed in one row, often laid out as two stacked rows, so 10U high racks for 40 or 44 modules. The "MOTM" format is part of the category of "5U format" modules, all sharing 5 standard rack units height.
  • The "500 Series" format defines "cassettes" of 3U height and 1U width. As such, it is similar to the MOTM form factor, except it is only 3U tall. The "500 Series" format is part of the category of "3U format" modules, all sharing a height of 3 standard rack units. Read the article on the (cmp.) 500 Series format for more details.
  • In Germany and the EU emerged the Eurorack format, a 3U tall format for modular synthesizer cards established by manufactuer Doepfer during the 1990s. The Eurorack specs in turn are based on IEC 60297-3 (DIN 41494) for subrack assemblies and "Eurocard" PCBs which are mounted inside. One slot in Eurorack racks is 0.20 inches wide or 5.08mm, with modules being either 2HP wide (HP for "horizontal pitch", or "TE" for German "Teileinheiten") or multiples of 2HP. So a common "slim" module is 20mm wide (4HP/ 4TE) and 45mm deep, a "wide" (double wide) module is 40.3mm wide. The "Eurorack" format is part of the category of "3U format" modules, all sharing a height of 3 standard rack units.
  • Top-of-Rack Cabling (ToR)

    What's the meaning of "UL Listed"?

    is a safety and quality seal issued by Underwriters Laboratories, a US certification authority. There's the seal of "UL Listed" and "UL Recognized".

    Universal rails

    UPS (Uninterruptible Power Supply)

    device or system to provide backup power to connected devices in case the main power fails, due to outages or malfunctions. Some UPSs also provide power filtering and conditioning, so power sags or spikes are filtered and do no harm to valuable or sensitive devices. backup power in UPS systems is usually implemented with a backup battery, being charged during normal operation and then taking over the power draw once the main power fails fails (or is switched off or cut, as in "Maintenance Bypass" (MBP) mode). Different Types of UPS are available, offering diffeernt levels of filtering and differences in how quick power is switched from mains to backup battery power: Standby Power System (SPS), Single-Conversion Systems, Double-Conversion Systems and Multi-Mode Systems, Online, Offline and Line interactive UPSs.

    Vertical Rack

    Special type of rack that allows equipment to be mounted vertically in order to save space, allow wall-mount installation in space -restrained environments or sometimes in-wall hidden installations in drywalls.

    Wall Mount Rack

    Rack cabinets or frames that can be bolted to a wall, usually elevated from the ground.

    Waterjet cutting

    also know as "Waterjet" is a technique where a machine uses high-pressure water to cut metal or other materials. A pump compresses water to over 30,000 psi and is then passed through a thin nozzle where a high-speed high-strength water jet stream emits. Computer controlled machines allow precise cuts similar to laser cutting. The water used may be pure water, for softer materials like plastic or foam, or abrasive water ("abrasive waterjet") where the liquid is carrying particles, like sand, to intensify the abrasiveness, the strength of the high-pressure water jet. Like laser cutting, the groove created by the jet ("kerf") is very thin. Also, waterjet has no thermal impact on the cut material and does not change the cut material's structure.

    More to read on Racks and Rack Mounting

    - 19" Rack in Wikipedia
    - Rack & Power section of the Open Compute Project
    - Data Storage Glossary

    On metal and metal forming

    The ASM Materials Education Foundation is publisher of an exhaustive series of metal handbooks for many decades now. Check the book "Sheet Metal Forming Fundamentals", edited by Taylan Altan and A. Erman Tekkaya (ISBN: 978-1-61503-842-8) and even more the "ASM Handbook Volume 14B: Metalworking: Sheet Forming" (link), edited by S.L. Semiatin (ISBN: 978-1-62708-186-3)

    Note on trademarks

    Many of the designations used by manufacturers and sellers to distinguish their products or services are claimed as trademarks. Where those designations appear in this text and Micropolis and/or the authors were aware of a trademark claim, the designations are mentioned along with their owners and may be additionally marked with a trademark symbol. Their use here in this rack mounting FAQ page is for educational use of the reader and is covered under nominative fair use. Micropolis is in no way suggesting support, sponsorship or endorsement of the owner of these trademarks. Only as much of such marks is used as is necessary to identify the trademark owner, product, or service.