19-inch rack

A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is 19 inches (48.3 cm) wide. The 19-inch dimension includes the edges, or "ears", that protrude on each side which allow the module to be fastened to the rack frame with screws. Common uses include computer server, telecom, broadcast video, lighting, audio, and scientific lab equipment.

Several 19-inch racks in a professional audio application
19-inch rack

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 mountable, or occasionally simply shelf. The height of the electronic modules is also standardized as multiples of 1.752 inches (44.50 mm) or one rack unit or U (less commonly RU).[1] The industry standard rack cabinet is 42U tall.

The term relay rack appeared first in the world of telephony.[2] By 1911, the term was also being used in railroad signaling.[3] There is little evidence that the dimensions of these early racks were standardized.

The 19-inch rack format with rack-units of 1.75 inches (44.45 mm) was established as a standard by AT&T around 1922 in order to reduce the space required for repeater and termination equipment for toll cables.

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 19½ inches between centers. The height of the different panels will vary, ... but ... in all cases to be a whole multiple of 1​34 inches".[4]

By 1934, it was an established standard with holes tapped for 12-24 screws with alternating spacings of 1.25 inches (31.75 mm) and 0.5 inches (12.70 mm) [5] The EIA standard was revised again in 1992 to comply with the 1988 public law 100-418, setting the standard U as 15.9 mm (0.626 in) + 15.9 mm (0.626 in) + 12.7 mm (0.500 in), making each "U" 44.50 millimetres (1.752 in).[6]

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 19-inch (482.6 mm) standard rack arrangement is widely used throughout the telecommunication, computing, audio, video, entertainment and other industries, though the Western Electric 23-inch standard, with holes on 1-inch (25.4 mm) centers, is still used in legacy ILEC/CLEC facilities.

DE-CIX GERMANY - Switch Rack (6218137120)
A 19-inch rack used for switches at the DE-CIX in Frankfurt, Germany

Nineteen-inch racks in two-post or four-post form hold most equipment in modern data centers, ISP facilities, and professionally designed corporate server rooms. They allow for dense hardware configurations without occupying excessive floorspace or requiring shelving.

Nineteen-inch racks are also often used to house professional audio and video equipment, including amplifiers, effects units, interfaces, headphone 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 ​132 inch (0.03125 inches or 0.794 millimetres) less than the allotted number of Us. Thus, a 1U rackmount computer is not 1.752 inches (44.5 mm) tall but is 1.721 inches (43.7 mm) tall. 2U would be 3.473 inches (88.2 mm) instead of 3.504 inches (89.0 mm). 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

Server rack rail dimensions
A typical section of 19-inch (482.6 mm) server rack rail


Originally, the mounting holes were tapped with a particular screw thread. When rack rails are too thin to tap, rivnuts or other threaded inserts 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.[7]

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,[8] and Versa Rail[9]) 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 nuts. 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 shear stress placed on the mounting rails and the leading edge of the equipment. As a result, 4-post racks have become common, with such racks featuring a mirrored pair of rear mounting posts. 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, i.e. 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 600 mm (23.62 in) or 800 mm (31.50 in) wide, and for them to be 600 mm (23.62 in), 800 mm (31.50 in) or 1,010 mm (39.76 in) 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 units) 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 of around 2 mm thickness (the official standard recommends a minimum of 1.9 mm), or of slightly thicker aluminum.

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. According to Telcordia Technologies 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,[10] with Zone 4 representing the most demanding environment.[11][12] GR-3108, Generic Requirements for Network Equipment in the Outside Plant (OSP), specifies the usable opening of seismic-compliant 19-inch racks.

Rails (slides)

3U rackmount system

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.[13] 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.[14]

Slides or rails for computers and other data processing equipment such as disk arrays 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

My Opera Server
Example of 19-inch computer rack

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 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 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 players will not work upside-down because the driving motor 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, 19 inches (482.60 mm) wide, and 36 inches (914.40 mm) 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.

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.[15] 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.[16] 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

19-inch equipment that needs to be moved often or protected from harsh treatment can be housed in an Air Transport Association of America (ATA) approved road case. Road cases are typically made from polyvinyl chloride (PVC) laminated plywood sides, joined by extruded aluminum edging, 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 rails 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.[17]

Fiberglass reinforced plastic case racks

In 1965, a durable fiber reinforced plastic 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, and DuPont’s Kevlar for demanding military and commercial uses.

Polyethylene molded case racks

Portable rack cases using a rotary-molded polyethylene 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.


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 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.[18]

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.


Computer keyboard and monitor mounted on a sliding tray in a rack

The formal standards for a 19-inch (482.6 mm) rack are available from the following:

  • Electronic Industries Alliance EIA-310-D, Cabinets, Racks, Panels, and Associated Equipment, dated September 1992. (Latest Standard Now REV E 1996)
  • Consumer Electronics Association CEA-310-E design requirements for Cabinets, Panels, Racks and Subracks., dated December 14, 2005
  • International Electrotechnical Commission - 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 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 0.625 inches (15.88 mm) wide, and are separated by a gap of 17.75 inches (450.85 mm), giving an overall rack width of 19 inches (482.60 mm). 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 18.312 inches (465.12 mm).[19]

The holes in the posts are arranged vertically in repeating sets of three, with center-to-center separations of 0.5 inches (12.70 mm), 0.625 inches (15.88 mm), 0.625 inches (15.88 mm). The hole pattern thus repeats every 1.75 inches (44.45 mm).

Holes so arranged can either be tapped (usually 10-32 UNF thread, or, less often, 6mm metric) or have square holes for cage nuts.

Rack unit (U)

Racks are divided into regions, 44.50 millimetres (1.752 in) in height, within which there are three complete hole pairs in a vertically symmetric pattern, the holes being centered 6.35 millimetres (0.25 in), 22.25 millimetres (0.88 in), and 38.15 millimetres (1.50 in) from the top or bottom of the region. Such a region is commonly known as a U, for unit, or, in German, HE, for Höheneinheit, and heights within racks are measured by this unit. Rack-mountable equipment is usually designed to occupy some integer number of U. For example, an oscilloscope might be 4U high, and rack-mountable computers are mostly between 1U and 4U high. A blade server enclosure might require 10U.

Occasionally, one may see fractional U devices such as a 1.5U server, 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 (200.2 centimetres or 78.82 inches) high, with 42U being a common configuration. Many wall-mounted industrial equipment enclosures have 19-inch rack rails to support mounting of equipment.

Related standards

11-foot frame

Frames for holding rotary-dial telephone equipment were generally 11 feet 6 inches (3.51 m) high. A series of studies led to the adoption of frames 7 feet (2.1 m) high, with modular widths in multiples of 1 foot 1 inch (0.33 m)—most often 2 feet 2 inches (0.66 m) wide.[20]

ETSI rack

Dimensions 19-inch ETSI rack
racks: 19" and ETSI

The ETSI rack is defined by the European Telecommunications Standards Institute (ETS 300 119). The distance of the right edge of the right mounting rail to the left edge of the left mounting rail is 535 millimetres (21.1 in). As 535 mm is very close to 21 inches, these racks are sometimes called 21-inch racks. The gap between the posts is 500 millimetres (19.69 in). As 19-inch equipment has a maximum width of 17 14 inches (438.15 mm), 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 150, 300, 600, 900 millimetres (5.9, 11.8, 23.6, 35.4 in) and two allowed depths are 300 and 600 millimetres (12 and 24 in). Hole spacing is 25 millimetres (0.98 in).

23-inch rack

SSEM Manchester museum close up
The 1948 original Manchester Baby and the 1998 working replica (pictured) were mounted on 23-inch racking.[21]

A 23-inch (580 mm) rack is used for housing telephone (primarily), computer, audio, 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 is a measure of vertical spacing and is common to both the 19 and 23 inch racks.

Hole spacing is either on 1-inch (25 mm) centers (Western Electric standard), or the same as for 19-inch (480 mm) racks (0.625 in or 15.9 mm spacing).

Open Rack

Open Rack is a mounting system designed by Facebook's Open Compute Project that has the same outside dimensions as typical 19-inch racks (e.g. 600 mm width), but supports wider equipment modules of 547 millimetres (21.5 in).[22]


Pictures of 19 inch racks


A server rack seen from the rear

Wikimedia Foundation Servers-8055 08

Wikimedia Foundation servers as seen from the front

Wikimedia Foundation Servers-8055 23

Wikimedia Foundation servers as seen from the rear

Wikimedia Foundation Servers-8055 02

Wikimedia Foundation servers as seen from the rear

See also


  1. ^ Tripp Lite: Rack Cabinet Buying Guide, http://www.tripplite.com/products/rack-buying-guide
  2. ^ Max Lowenthal, The New Exchange of the Central New York Telephone and Telegraph Co. at Syracuse, N.Y., The Electrical Engineer, Vol XXVII, No. 561 (Feb 2, 1899); pages 142-147. The term relay rack appears on page 144 at the bottom of column 1.
  3. ^ New Electric Interlocking at Allentown, PA, The Signal Engineer, Vol. 4, No. 9 (Sept. 1911); pages 344–345.
  4. ^ Charles S. Demarest, Telephone Equipment for Long Cable Circuits, Bell System Technical Journal Vol.2, Issue 2, April 1923, page 139.
  5. ^ G. Robt. Mezger (W2BLL), The Relay Rack in Amateur Construction, QST Vol. 18 (1934), American Radio Relay League.
  6. ^ ANSI/EIA-310-D-1992
  7. ^ The Computer Rack section of The University of Iowa's DEC PDP-8, documents a relay rack made in 1965; Nov. 2011.
  8. ^ "Define: Rack Hole Types". www.server-racks.com.
  9. ^ "What is a Versa Rail". www.server-racks.com.
  10. ^ Telcordia GR-63-CORE, NEBS™ Requirements: Physical Protection
  11. ^ "Telcordia GR-1502-CORE, Central Office/Network Environment Detail Engineering Generic Requirements". Archived from the original on 2009-07-29. Retrieved 2009-07-27.
  12. ^ Seismic Enclosures Provide an Extra Measure of Protection
  13. ^ William B. George, Chassis Slide Mechanism, U.S. Patent 3,092,429, granted June 4, 1963.
  14. ^ Scott F. Herbert, Electronic Assembly Chassis Supporting Track, U.S. Patent 2,809,085, granted Oct. 8, 1957.
  15. ^ "Telcordia GR-3108-CORE, NEBS™ Requirements for Telecommunications Data Center Equipment and Spaces". Archived from the original on 2009-07-27. Retrieved 2009-07-24.
  16. ^ "Aluminum Relay Rack" (PDF). Bud Industries. Retrieved 2017-12-26.
  17. ^ "Standard Rack Mount Cases". Anvil Case. Retrieved 2017-12-26.
  18. ^ "Data Center Cooling | Pentair". schroff.pentair.com. Retrieved 2017-08-27.
  19. ^ "The Server Rack FAQ - Define EIA-310". www.server-racks.com.
  20. ^ Keller, A. C. (January 1964). "Recent Developments in Bell System Relays — Particularly Sealed Contact and Miniature Relays". Bell Labs Technical Journal. 43: 15–44. doi:10.1002/j.1538-7305.1964.tb04057.x.
  21. ^ The Manchester Baby : The First Stored Program Computer. Google. 2013.
  22. ^ "Open Rack 1.0 Specification Available Now". Open Compute.

External links

  • Media related to 19"-Racks at Wikimedia Commons
Aster CT-80

The Aster CT-80, an early (1982) home/personal computer developed by the small Dutch company MCP (later renamed to Aster Computers), was sold in its first incarnation as a kit for hobbyists. Later it was sold ready to use. It consisted of several Eurocard PCB's with DIN 41612 connectors, and a backplane all based on a 19-inch rack configuration. It was the first commercially available Dutch personal/home computer. The Aster computer could use the software written for the popular Tandy TRS-80 computer while fixing many of the problems of that computer, but it could also run CP/M software, with a big amount of free memory Transient Program Area, (TPA) and a full 80×25 display, and it could be used as a Videotext terminal. Although the Aster was a clone of the TRS-80 Model I it was in fact more compatible with the TRS-80 Model III, and ran all the software of these systems including games. It also had a built in speaker which was compatible with such games software.

DIN 41612

DIN 41612 is a DIN standard for electrical connectors that are widely used in rack based electrical systems. Standardisation of the connectors is a pre-requisite for open systems, where users expect components from different suppliers to operate together. The most widely known use of DIN 41612 connectors is in the VMEbus system. They were also used by NuBus. The standard has subsequently been upgraded to international standards IEC 60603-2 and EN 60603-2.

DIN 41612 connectors are used in STEbus,Futurebus, VMEbus, Multibus II, NuBus, VXI Bus,

eurocard TRAM motherboards,

and Europe Card Bus,

all of which typically use male DIN 41612 connectors on Eurocards plugged into female DIN 41612 on the backplane in a 19-inch rack chassis.

Eurocard (printed circuit board)

Eurocard is a European standard format for printed circuit board (PCB) cards that can be plugged together into a standard chassis which, in turn, can be mounted in a 19-inch rack. The chassis consists of a series of slotted card guides on the top and bottom, into which the cards are slid so they stand on end, like books on a shelf. At the spine of each card is one or more connectors which plug into mating connectors on a backplane that closes the rear of the chassis.

Fujitsu Eagle

The Fujitsu M2351 "Eagle" was a hard disk drive with an SMD interface that was used on many servers in the mid-1980s. It offered an unformatted capacity of 470 MB in 10 1⁄2 inches (270 mm) (6U) of 19-inch rack space, at a retail price of about US$10,000.

The data density, access speed, reliability, use of a standard interface, and price point combined to make it a very popular product used by many system manufacturers, such as Sun Microsystems. The Eagle was also popular at installations of DEC VAX systems, as third-party storage systems were often dramatically more cost-effective and space-dense than those vendor-supplied.

The model 2351A incorporated eleven platters rotating at 3,960 rpm, taking half a minute to spin up. The Eagle used 10.5-inch-diameter (270 mm) platters, unlike most of its competitors, which still used the 14-inch (360 mm) standard set in 1962 by the IBM 1311. One moving head accessed each data surface (20 total), one more head was dedicated to the servo mechanism. The model 2351AF added 60 fixed heads (20 surfaces × 3 cylinders) for access to a separate area of 1.7 MB.

The Eagle achieved a data transfer rate of 1.8 MB/s (a contemporary 5 1⁄4-inch (130 mm) PC disk would only deliver 0.4 MB/s).

Power consumption (of the drive alone) was about 600 watts.

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 mounted equipment. One HP is 0.2 inches (5.08 mm) wide. A standard 19-inch rack is 95 HP wide of which 84 HP is typically usable. A standard 23-inch rack is 115 HP wide of which 104HP is typically usable.

ISO 7736

International standard ISO 7736 defines a standard size for car audio head units and enclosures. The standard was originally established by the German standards body Deutsches Institut für Normung as DIN 75490, and is therefore commonly referred to as the "DIN car radio size". It was adopted as an international standard in 1984.

Head units generally come in either single DIN (180 x 50 mm panel) or double DIN (180 x 100.3 mm panel) size. The depth is not standardized; as a result, some cars such as the Opel Manta / Ascona have the correct sized front aperture but will accommodate few DIN sized radios other than the original due to the shallow depth; this despite the vehicle being manufactured as late as 1988. The US standard for a DIN radio is 6.83" x 2" (although the actual 180 mm width converts to something like 7-3/32" so most people use 7-1/8" to allow for clearance) and the Double DIN sized radio is a 7" x 4". Some radios in Japanese Kei cars do not conform to the DIN standard however.


The TSEC/KW-26, code named ROMULUS, (in 1966 the machine based encryption system was not code-named "Romulus," rather the code-name was "Orion," at least in the US Army's variant) was an encryption system used by the U.S. Government and, later, by NATO countries. It was developed in the 1950s by the National Security Agency (NSA) to secure fixed teleprinter circuits that operated 24 hours a day. It used vacuum tubes and magnetic core logic, replacing older systems, like SIGABA and the British 5-UCO, that used rotors and electromechanical relays.

A KW-26 system (transmitter or receiver) contained over 800 cores and approximately 50 vacuum-tube driver circuits, occupying slightly more than one half of a standard 19-inch rack. Most of the space in the rack and most of the 1 kW input power were required for the special-purpose vacuum tube circuits needed to provide compatibility with multiple input and output circuit configurations. The military services' requirements for numerous modes and speeds significantly increased costs and delayed delivery. NSA says it is doubtful that more than three or four of the possible configurations were ever used.

The KW-26 used an NSA-developed encryption algorithm based on shift registers. The algorithm produced a continuous stream of bits that were xored with the five bit Baudot teleprinter code to produce ciphertext on the transmitting end and plaintext on the receiving end. In NSA terminology, this stream of bits is called the key. The information needed to initialize the algorithm, what most cryptographers today would call the key, NSA calls a cryptovariable. Typically each KW-26 was given a new cryptovariable once a day.

NSA designed a common fill device (CFD), for loading the cryptovariable. It used a Remington Rand (UNIVAC) format punched card (45 columns, round holes). The operator inserted the daily key card into the CFD and closed the door securely, locking the card in place. Decks of cards were created by NSA and sent by courier. The cards were strictly accounted for.

Because the KW-26 used a stream cipher, if the same key card was ever used twice, the encryption could be broken. To prevent re-use, the card was automatically cut in half upon reopening the CFD. As the units aged, the card reader contacts became less dependable, and operators resorted to various tricks, such as hitting the card reader cover with a screwdriver, to get them to work properly. Card readers were cleaned and the spring loading of the contacts checked as part of the routine maintenance of the device.

Because the KW-26 sent a continuous stream of bits, it offered traffic-flow security. Someone intercepting the ciphertext stream had no way to judge how many real messages were being sent, making traffic analysis impossible. One problem with the KW-26 was the need to keep the receiver and transmitter units synchronized. The crystal controlled clock in the KW-26 was capable of keeping both ends of the circuit in sync for many hours, even when physical contact was lost between the sending and receiving units. This capability made the KW-26 ideally suited for use on unreliable HF radio circuits. However, when the units did get out of sync, a new key card had to be inserted at each end. The benefit of traffic-flow security was lost each time new cards were inserted. In practice, operational protocol led to the cards being replaced more often than was desirable to maintain maximum security of the circuit. This was especially so on radio circuits, where operators often changed the cards many times each day in response to a loss of radio connectivity. In any case, it was necessary to change the cards at least once per day to prevent the cypher pattern from repeating.

Early KW-26 units protected the CRITICOMM network, used to protect communications circuits used to coordinate signals intelligence gathering. The initial production order for this application, awarded to Burroughs in 1957, was for 1500 units. Other services demanded KW-26's and some 14000 units were eventually built, beginning in the early 1960s, for the U.S. Navy, Army, Air Force, Defense Communications Agency, State Department and the CIA. It was provided to U.S. allies as well.

When the USS Pueblo was captured by North Korea in 1968, KW-26's were on board. In response, the NSA had modifications made to other units in the field, presumably changing the crypto algorithm in some way, perhaps by changing the shift register feedback taps. Starting in the mid-1980s, the KW-26 system was decommissioned by NSA, being replaced by the more advanced solid-state data encryptor, TSEC/KG-84.

Micro data center

A micro data center (MDC) is a smaller or containerized (modular) data center architecture that is designed to solve different sets of problems that take different types of compute workload that does not require traditional facilities. Whereas the size may vary from rack to container, a micro data center may include fewer than 4 servers in a single 19-inch rack. It may come with built-in security systems, cooling systems, and/or fire protection. Typically there are standalone rack-level systems containing all the components of a 'traditional' data center. including in rack cooling, power supply, power backup, security, fire and suppression. They could be rapidly deployed indoors or outdoors or also in rugged terrains.

Mid 2017, introduced by DOME, technology was demonstrated that packs 64 high-performance servers, storage, networking, power and cooling integrated in a 2U 19" rack-unit. This packaging, sometimes called 'datacenter-in-a-box' allows deployments in spaces where traditional data centers do not fit, such as factory floors (IOT) and dense city centers especially for edge-computing and edge-analytics.

Their size, versatility and plug & play features make them ideal for use in remote locations, for a branch office, or even for use temporarily at locations that are in high risk zones.

Quantel Mirage

The Quantel Mirage, or DVM8000/1 "Digital Video Manipulator", was a digital real-time video effects processor introduced by Quantel in 1982. It was capable of warping a live video stream by texture mapping it onto an arbitrary three-dimensional shape, around which the viewer could freely rotate or zoom in real-time. It could also interpolate, or morph, between two different shapes. It was considered the first real-time 3D video effects processor.

The Mirage was programmable - new shapes could be created by writing programs in the Pascal programming language on an attached Hewlett Packard computer. This made the device extremely flexible, but such programming was difficult and it became a highly specialized skill known by few. The programming of the HP mini computer was so complex that only basic canned effects would be practically used by video editors in productions.

Physically, the Mirage was a large device whose processing equipment filled a full-height 19-inch rack, weighed 400 kilograms and consumed over 4 kilowatts of electrical power.

The Quantel Mirage did never-before seen effects, but required heavy math/geometrical programming via the HP computer to define the basic shapes that real-time video would be mapped onto. One of the effects shown on the National Association of Broadcasters trade-show floor to introduce the Mirage was a flattened Coke soft-drink can on video. The Mirage in real-time re-assembled the can on a tube, then allowed you to tumble or travel within it while it rotated with partial transparency - allowing you to see the Coke logo in reverse on the opposite side of the can as it would turn.

One famous Mirage user was Mike Oldfield, who purchased one for his extensive home music studio and video production facility. Signature Mirage effects can be seen in the Wind Chimes video album, in the form of rotating spiky spheres and granulated morphing effects.

A common spinning globe effect can be seen on the opening of USA for Africa's "We Are The World," and the Cyndi Lauper "Girls Just Wanna Have Fun" music videos.


The RK05 DECpack was a moving head magnetic disk drive manufactured by the Digital Equipment Corporation of Maynard, Massachusetts. It stored approximately 2.5 MB on a 14", single-platter IBM-2315-style front-loading removable disk cartridge. The cartridge permitted users to have relatively unlimited off-line storage and to have very fast access to such data. At the time DEC had numerous operating systems for each computer architecture so operating systems could also be changed quickly. The RK05 was the disk successor to DECtape for personal, portable, and expandable storage. While the smallest practical configuration was two drives, many systems had four or more drives.

Occupying 10.5 inches (6U) of space in a standard 19-inch rack, the drive was competitive at the time. The cartridge contained a single, 14" aluminum platter coated with iron oxide in an epoxy binder. The two ferrite and ceramic read/write heads were pressed towards the disk by spring arms, floating on an air bearing maintained by the rotation of the disk. They were positioned by a voice coil actuator using a linear optical encoder for feedback. The track density was 100 tracks-per-inch. The bit density along the track was about 2200 bits-per-inch. Discrete electronics computed the velocity profile for seeks commanded by the controller. An absolute filter (HEPA filter) provided pressurized air to the cartridge, excluding most contaminants that would otherwise cause head crashes.

When used on 16-bit systems such as the PDP-11, the drive stored roughly 1.2 megawords. When used on 12-bit systems such as the PDP-8, the drive stored 1.6 megawords (so roughly the same bit capacity, albeit formatted differently). Multiple drives were daisy chained from their controller using Unibus cabling; a terminator was installed in the farthest drive.

The 16-bit (Unibus) controller was known as the RK11; it allowed the connection of up to eight RK05 drives. Seeks could be overlapped among the drives but only one drive at a time could transfer data.

The most-common 12-bit (Omnibus) controller was known as the RK8E; it supported up to four RK05 drives. The RK05 disk had more than 4096 sectors and so could not be addressed completely by a single PDP-8 12-bit word. To accommodate this, the OS/8 operating system split each drive into two logical volumes, for example, RKA0 and RKB0, representing the outermost and innermost cylinders of the drive.

RLX Technologies

RLX Technologies was a computer company based in The Woodlands, Texas. It marketed what is now known as a blade server. Founded in 1999 by Christopher Hipp, one of the inventors of the blade server, and former Compaq Computers employees, the company pioneered the use of blade servers, a compact, stripped-down computer server that includes all of the necessary components to operate as a computer while taking up minimal space on a standard 19-inch rack and minimizing power consumption. It became part of Hewlett-Packard in 2005.

RS Integrator

The RS Integrator is a series of analog modular synthesizer systems made by British company Analogue Systems, which had previously manufactured the TH48 step sequencer and FB3 Filterbank.

As with Doepfer's similar A-100 system, modules are designed to be mounted in a standard 19-inch rack enclosure, each module measuring 3U in height. Modules are patched using standard mono miniature (3.5 mm) leads.

Various controller keyboards are available within the RS Integrator series, including the Sorceror (sic), which can house modules inside its wooden enclosure.

Rack rail

A Rack rail, or rack strip, is used to mount rackable electronic hardware and 19-inch rack mount accessories within a 19-inch rack. Within a rack a minimum of two rack rails are required to mount equipment. The height of rack rail is determined by the number of rack units required for mounting the equipment.

The design of racks and rack rails is specified in ECIA - EIA/ECA-310

Each rack unit (U) is equivalent to 1 3⁄4 in (44 mm). Most rack rail is in sizes from 2 units high (3 1⁄2 in or 89 mm) to 54 units high (78 3⁄4 in or 2,000 mm).

Rack unit

A rack unit (abbreviated U or RU) is a unit of measure defined as 1 3⁄4 inches (44.45 mm). 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 the height of the frame or equipment is expressed as multiples of rack units. For example, a typical full-size rack cage is 42U high, while equipment is typically 1U, 2U, 3U, or 4U high.

Rackmount KVM

A KVM is a computer input/output device offering the combination of a keyboard, video monitor and mouse (pointing device). They are typically constructed to fit into a 19-inch rack although there are manufacturers who offer a KVM that can be mounted to a flat surface such as a control console.


SiCortex was a supercomputer manufacturer founded in 2003 and headquartered in Clock Tower Place,

Maynard, Massachusetts. On 27 May 2009, HPCwire reported that the company had shut down its operations, laid off most of its staff, and is seeking a buyer for its assets. The Register reported that Gerbsman Partners was hired to sell SiCortex's intellectual properties. While SiCortex had some sales, selling at least 75 prototype supercomputers to several large customers, the company had never produced an operating profit and ran out of venture capital. New funding could not be found.

The company built and marketed a family of clusters of between 12 and 972 compute nodes, connected in a Kautz graph. The clusters are the SC5832, SC648 and SC072. It was reported that the company has been working on the next generation of clusters since March 2009, but development ceased when operations were closed.

The SC5832 is a high-end model housed in a cabinet. It has 972 nodes, 5,832 cores and 972 to 7,776 GB of memory. It uses a diameter-6 Kautz graph for 2,916 links. The SC648 is a mid-range model housed in a standard 19-inch rack. Each rack may contain two systems. It has 108 nodes, 648 cores and 108 to 864 GB of memory. It uses a diameter-4 Kautz graph for 324 links. The SC072 is a desktop model for developing software.

Each node is system-on-chip (SoC), codenamed ICE9, consisting of six cores that implement the MIPS64 instruction set architecture (ISA). Each core has a 32 KB instruction cache and a 32 KB data cache. The six cores have their own 256 KB L2 cache, which can be accessed by other cores. The MIPS cores execute instructions in-order and have a six-stage pipeline. They can issue and execute two instructions per cycle for peak double-precision (64-bit) performance of 1 GFLOPS at 500 MHz. This was later increased to 1.4 GFLOPS when the clock frequency of the SoC was increased to 700 MHz when the SoC was fabricated in a 90 nm process. The SoC contains two DDR2 memory controllers, each controlling a single DIMM. Each node can have 1 to 8 GB of memory. The SoC also implements a 8x PCI Express controller. The cluster interconnect is implemented by a DMA engine fabric switch. Each cluster interconnect provides a maximum bandwidth of 2 GB/s.

Message passing, via MPI, is the presumptive programming model. SiCortex systems run a customized Linux distribution derived from Gentoo Linux.

Transit case

A transit case is a hard-sided case intended for protecting 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. Some transit cases are provided with foam inserts that completely fill the interior and the user can pluck out pieces to make the case fit a particular application. Many camera cases are built in this fashion allowing the user to tailor the interior foam to their particular equipment. The outside of the transit case provides protection against the environment and a first level of protection against mechanical damage such as shock. The interior foam or other structure cushions the equipment against shock and vibration and some protection against rapid temperature changes.

The difference between a transit case and a suit case is a transit case is configured with internal foam or other structure to hold and protect specific items. A suit case is an empty case in which items can be placed in any order with no predefined locations other than features such as internal pockets. An empty transit case can be used as a suit case.

Transit cases can be procured in virtually any size to contain something very small to very large which may require several people or a fork lift to move.

Road cases are a subset of transit cases. Road cases are traditionally manufactured with plywood sides and metal corner braces. Transit cases are usually molded or formed from plastic, composite materials or aluminum so the top and bottom sections are seamless.

A rack case is a transit case with provision for mounting rackmount equipment such as amplifiers, computers, displays, radios, encryption devices, and so forth. In many cases, the internal 19-inch rack is mounted to the transit case via shock absorbing mounts giving the rack sway space to attenuate shocks and bumps that might be seen during shipment and handling.

Varian Data Machines

Varian Data Machines was a division of Varian Associates which sold minicomputers. It entered the market in 1967 through acquisition of Decision Control Inc. (DCI) in Newport Beach, California. It met stiff competition and was bought by Sperry Corporation in 1977.The DCI 1966 DATA/620 was a parallel, binary 16-bit general-purpose digital computer with magnetic-core memory expandable to 32,768 words. An 18-bit word length (for data, not addresses) was optionally available. A basic machine cycle took 1.8 microseconds, and the core memory read time was 700 nanoseconds. The computers uses two's complement arithmetic and had four main registers - accumulator A, accumulator extension B, an index register X and a program counter register. Addressing modes were direct, immediate and indexed. The instruction set had more than one hundred arithmetic, logic and control instructions and some variants supported microprogramming. These models used a hardware front panel console that allowed starting and stopping the machine, examining memory and registers and changing memory or registers with front-panel switches. It used "Versalogic" (discrete transistorized) circuits with a bit-sliced architecture.:21The 620/i:1 shipped in June 1967; it and subsequent series were made with integrated circuit transistor–transistor logic from the 7400 series. The system was packaged in a 19-inch rack and consumed 340 watts at 120 V AC. The 620/F was a variation with a faster machine cycle time of 750 nanoseconds.

The ruggedized R-620/i was announced in 1968.A lower cost 520/i shipped in October 1968The 620/L-100 was released in 1973. It had a cycle time of 950 nanoseconds and a more compact system chassis than the 620/F. The Sperry V70 series had semiconductor memory, but could also support magnetic core. Various models were released between 1972 and 1977.Varian V72 computer systems were installed at Bruce Nuclear Generating Station on the eastern shore of Lake Huron in Ontario, Canada, as the digital control computer system that monitors and controls the major reactor and power plant functions. As of February 2017 these were still in operation and scheduled to be replaced by more modern systems in 2018 and 2019.

IEC standards
ISO/IEC standards

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