The inch (abbreviation: in or ) is a unit of length in the (British) imperial and United States customary systems of measurement. It is equal to ​136 yard or ​112 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb. Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as exactly 25.4 mm.

Unit systemimperial/US units
Unit oflength
1 in in ...... is equal to ...
   imperial/US units   1/36 yd
1/12 ft
   metric (SI) units   25.4 mm


The English word "inch" (Old English: ynce) was an early borrowing from Latin uncia ("one-twelfth; Roman inch; Roman ounce") not present in other Germanic languages.[1] The vowel change from Latin /u/ to Old English /y/ (which became Modern English /ɪ/) is known as umlaut. The consonant change from the Latin /k/ (spelled c) to English /tʃ/ is palatalisation. Both were features of Old English phonology; see Phonological history of Old English § Palatalization and Germanic umlaut § I-mutation in Old English for more information.

"Inch" is cognate with "ounce" (Old English: ynse), whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce.[2]

In many other European languages, the word for "inch" is the same as or derived from the word for "thumb", as a man's thumb is about an inch wide (and this was even sometimes used to define the inch[3]). Examples include Afrikaans: duim; Catalan: polzada ("inch") and polze ("thumb"); Czech: palec ("thumb"); Danish and Norwegian: tomme ("inch") tommel ("thumb"); Dutch: duim; French: pouce; Hungarian: hüvelyk; Italian: pollice; Portuguese: polegada ("inch") and polegar ("thumb"); Slovak: palec ("thumb"); Spanish: pulgada ("inch") and pulgar ("thumb"); and Swedish: tum ("inch") and tumme ("thumb") and Russian: дюйм ("duim").


The inch is a commonly used customary unit of length in the United States,[4] Canada,[5][6] and the United Kingdom.[7] It is also used in Japan for electronic parts, especially display screens. In most of continental Europe, the inch is also used informally as a measure for display screens. For the United Kingdom, guidance on public sector use states that, since 1 October 1995, without time limit, the inch (along with the foot) is to be used as a primary unit for road signs and related measurements of distance (with the possible exception of clearance heights and widths)[8] and may continue to be used as a secondary or supplementary indication following a metric measurement for other purposes.[7]

The international standard symbol for inch is in (see ISO 31-1, Annex A) but traditionally the inch is denoted by a double prime, which is often approximated by double quotes, and the foot by a prime, which is often approximated by an apostrophe. For example, three feet two inches can be written as 3′ 2″. (This is akin to how the first and second "cuts" of the hour and degree are likewise indicated by prime and double prime symbols.) Subdivisions of an inch are typically written using dyadic fractions with odd number numerators; for example, two and three eighths of an inch would be written as 2 3/8″ and not as 2.375″ nor as 2 6/16″.

Inch tape
Measuring tape calibrated in 32nds of an inch


1 international inch is equal to:


Inch converter
Mid-19th century tool for converting between different standards of the inch

The earliest known reference to the inch in England is from the Laws of Æthelberht dating to the early 7th century, surviving in a single manuscript, the Textus Roffensis from 1120.[11] Paragraph LXVII sets out the fine for wounds of various depths: one inch, one shilling, two inches, two shillings, etc.[l]

An Anglo-Saxon unit of length was the barleycorn. After 1066, 1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, with the barleycorn being the base unit.[14] One of the earliest such definitions is that of 1324, where the legal definition of the inch was set out in a statute of Edward II of England, defining it as "three grains of barley, dry and round, placed end to end, lengthwise".[14]

Similar definitions are recorded in both English and Welsh medieval law tracts.[15] One, dating from the first half of the 10th century, is contained in the Laws of Hywel Dda which superseded those of Dyfnwal, an even earlier definition of the inch in Wales. Both definitions, as recorded in Ancient Laws and Institutes of Wales (vol i., pp. 184, 187, 189), are that "three lengths of a barleycorn is the inch".[16]

King David I of Scotland in his Assize of Weights and Measures (c. 1150) is said to have defined the Scottish inch as the width of an average man's thumb at the base of the nail, even including the requirement to calculate the average of a small, a medium, and a large man's measures.[17] However, the oldest surviving manuscripts date from the early 14th century and appear to have been altered with the inclusion of newer material.[18]

In 1814, Charles Butler, a mathematics teacher at Cheam School, recorded the old legal definition of the inch to be "three grains of sound ripe barley being taken out the middle of the ear, well dried, and laid end to end in a row", and placed the barleycorn, not the inch, as the base unit of the English Long Measure system, from which all other units were derived.[19] John Bouvier similarly recorded in his 1843 law dictionary that the barleycorn was the fundamental measure.[20] Butler observed, however, that "[a]s the length of the barley-corn cannot be fixed, so the inch according to this method will be uncertain", noting that a standard inch measure was now (by his time) kept in the Exchequer chamber, Guildhall, and that was the legal definition of the inch.[19] This was a point also made by George Long in his 1842 Penny Cyclopædia, observing that standard measures had since surpassed the barleycorn definition of the inch, and that to recover the inch measure from its original definition, in the event that the standard measure were destroyed, would involve the measurement of large numbers of barleycorns and taking their average lengths. He noted that this process would not perfectly recover the standard, since it might introduce errors of anywhere between one hundredth and one tenth of an inch in the definition of a yard.[21]

Before the adoption of the international yard and pound, various definitions were in use. In the United Kingdom and most countries of the British Commonwealth, the inch was defined in terms of the Imperial Standard Yard. The United States adopted the conversion factor 1 metre = 39.37 inches by an act in 1866.[22] In 1893, Mendenhall ordered the physical realization of the inch to be based on the international prototype metres numbers 21 and 27, which had been received from the CGPM, together with the previously adopted conversion factor.[23]

In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known.[24][25]

In 1946, the Commonwealth Science Congress recommended a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth. This was adopted by Canada in 1951,[26][27] the United States on 1 July 1959,[28][29][30] Australia in 1961,[31] effective 1 January 1964,[32] and the United Kingdom in 1963,[33] effective on 1 January 1964.[34] The new standards gave an inch of exactly 25.4 mm, 1.7 millionths of an inch longer than the old imperial inch and 2 millionths of an inch shorter than the old US inch.[35]

Related units

US Survey inches

The United States retains the 1/39.37-metre definition for survey purposes, producing a 2 millionth part difference between standard and US survey inches.[36] This is approximately 1/8 inch per mile. In fact, 12.7 kilometres is exactly 500,000 standard inches and exactly 499,999 survey inches. This difference is significant when doing calculations in State Plane Coordinate Systems with coordinate values in the hundreds of thousands or millions of feet.

Continental inches

Before the adoption of the metric system, several European countries had customary units whose name translates into "inch". The French pouce measured 27.0 mm, at least when applied to describe the calibre of artillery pieces. The Amsterdam foot (voet) consisted of 11 Amsterdam inches (duim). The Amsterdam foot is about 8% shorter than an English foot.

Scottish inch

The now obsolete Scottish inch (Scottish Gaelic: òirleach), 1/12 of a Scottish foot, was about 1.0016 imperial inches (about 25.4406 mm).[37] It was used in the popular expression Gie 'im an inch, an he'll tak an ell, in English "Give him an inch and he'll take an ell", first published as "For when I gave you an inch, you tooke an ell" by John Heywood in 1546.[38] (The ell, equal to 37 inches (about 940 mm), was in use in England until 1685.)[39] Modern versions of the saying include "Give him an inch and he'll take a mile" and "Give him an inch and he'll take a yard".[40]

See also


  1. ^ Used in machining.
  2. ^ Used in machining and papermaking.
  3. ^ Formerly used in American English but now often avoided to prevent confusion with millimeters.
  4. ^ Used by the Australian Bureau of Meteorology for measuring rainfall until 1973[9]
  5. ^ a b Part of John Locke's proposal for decimalization of English measures[10]
  6. ^ Used in gunmaking.
  7. ^ Used in botany.
  8. ^ Used in button manufacturing.
  9. ^ Used in typography.
  10. ^ Used in American and British shoe sizes.
  11. ^ Used in measuring the height of horses.
  12. ^ Old English: Gif man þeoh þurhstingð, stice ghwilve vi scillingas. Gife ofer ynce, scilling. æt twam yncum, twegen. ofer þry, iii scill. Translation (taken from Attenborough 1922, p. 13): If a thigh is pierced right through, 6 shillings compensation shall be paid for each stab. For a stab over an inch [deep], 1 shilling; for a stab between 2 and 3 inches, 2 shillings; for a stab over 3 inches 3 shillings.[12][13]



  1. ^ "inch, n.¹", Oxford English Dictionary, Oxford: Oxford University Press.
  2. ^ "ounce, n.¹", Oxford English Dictionary, Oxford: Oxford University Press.
  3. ^ "Inch | unit of measurement". Encyclopedia Britannica. Retrieved 28 March 2019.
  4. ^ "Corpus of Contemporary American English". Brigham Young University. US. Retrieved 5 December 2011. lists 24,302 instances of inch(es) compared to 1548 instances of centimeter(s) and 1343 instances of millimeter(s).
  5. ^ "Weights and Measures Act" (PDF). Canada. 1985. p. 37. Retrieved 11 January 2018 – via Justice Laws Website.
  6. ^ "Weights and Measures Act". Canada. 1 August 2014. p. 2. Retrieved 18 December 2014 – via Justice Laws Website. Canadian units (5) The Canadian units of measurement are as set out and defined in Schedule II, and the symbols and abbreviations therefore are as added pursuant to subparagraph 6(1)(b)(ii).
  7. ^ a b "Guidance Note on the use of Metric Units of Measurement by the Public Sector" (PDF). UK: Department for Business Innovation and Skills. 2007. Archived from the original (PDF) on 12 December 2012. Retrieved 12 December 2014.
  8. ^ "The Traffic Signs Regulations and General Directions 2002 - No. 3113 - Schedule 2 - Regulatory Signs". UK: The National Archives. 2002. Retrieved 25 April 2013.
  9. ^ "Climate Data Online – definition of rainfall statistics". Australia: Bureau of Meteorology. Retrieved 10 June 2012.
  10. ^ "Of Human Understanding", The Works of John Locke Esq., Vol. I, London: John Churchill, 1714, p. 293.
  11. ^ Goetz, Hans-Werner; Jarnut, Jörg; Pohl, Walter (2003). Regna and Gentes: The Relationship Between Late Antique and Early Medieval Peoples and Kingdoms in the Transformation of the Roman World. BRILL. p. 33. ISBN 978-90-04-12524-7. Retrieved 14 May 2012.
  12. ^ Wilkins, David (1871). Councils and Ecclesiastical Documents Relating to Great Britain and Ireland: English church during the Anglo-Saxon period: A.D. 595-1066. Oxford, UK: Clarendon Press. p. 48. Retrieved 18 December 2014.
  13. ^ Duncan, Otis Dudley (1984). Notes on social measurement: historical and critical. US: Russell Sage Foundation. p. 87. ISBN 978-0-87154-219-9. Retrieved 27 November 2011.
  14. ^ a b Klein, H. Arthur (1974). The world of measurements: masterpieces, mysteries and muddles of metrology. New York, US: Simon and Schuster.
  15. ^ Hawkes, Jane; Mills, Susan (1999). Northumbria's Golden Age. UK: Sutton. p. 310. ISBN 978-0-7509-1685-1.
  16. ^ Williams, John (1867). "The civil arts — mensuration". The Traditionary Annals of the Cymry. Tenby, UK: R. Mason. pp. 243–245.
  17. ^ Swinton, John (1789). A proposal for uniformity of weights and measures in Scotland. printed for Peter Hill. p. 134. Retrieved 27 February 2012.
  18. ^ Gemmill, Elizabeth; Mayhew, Nicholas (22 June 2006). Changing Values in Medieval Scotland: A Study of Prices, Money, and Weights and Measures. UK: Cambridge University Press. p. 113. ISBN 978-0-521-02709-0. Retrieved 27 February 2012.
  19. ^ a b Butler, Charles (1814). An Easy Introduction to the Mathematics. Oxford, UK: Bartlett and Newman. p. 61.
  20. ^ Bouvier, John (1843). "Barleycorn". A Law Dictionary: With References to the Civil and Other Systems of Foreign Law. Philadelphia, US: T. & J. W. Johnson. p. 188.
  21. ^ Long, George (1842). "Weights & Measures, Standard". The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge. London, UK: Charles Knight & Co. p. 436.
  22. ^ Judson, Lewis V (October 1963). Weights and Measures Standards of the United States - a brief history - NBS publication 447. United States Department of Commerce. p. 10–11.
  23. ^ T. C. Mendenhall, Superintendent of Standard Weights and Measures (5 April 1893). "Appendix 6 to the Report for 1893 of the Coast and Geodetic Survey" (PDF). Archived from the original (PDF) on 30 September 2012.
  24. ^ National Conference on Weights and Measures; United States. Bureau of Standards; National Institute of Standards and Technology (US) (1936). Report of the ... National Conference on Weights and Measures. US Department of Commerce, Bureau of Standards. p. 4. Retrieved 2 August 2012.
  25. ^ Wandmacher, Cornelius; Johnson, Arnold Ivan (1995). Metric Units in Engineering--going SI: How to Use the International Systems of Measurement Units (SI) to Solve Standard Engineering Problems. ASCE Publications. p. 265. ISBN 978-0-7844-0070-8. Retrieved 2 August 2012.
  26. ^ Howlett, L. E. (1 January 1959). "Announcement on the International Yard and Pound". Canadian Journal of Physics. 37 (1): 84–84. Bibcode:1959CaJPh..37...84H. doi:10.1139/p59-014 – via NRC Research Press.
  27. ^ National Conference on Weights and Measures; United States. Bureau of Standards; National Institute of Standards and Technology (US) (1957). Report of the ... National Conference on Weights and Measures. US Department of Commerce, Bureau of Standards. pp. 45–6. Retrieved 2 August 2012.
  28. ^ Astin, A.V.; Karo, H. A.; Mueller, F.H. (25 June 1959). "Refinement of Values for the Yard and the Pound" (PDF). US Federal Register.
  29. ^ United States. National Bureau of Standards (1959). Research Highlights of the National Bureau of Standards. US Department of Commerce, National Bureau of Standards. p. 13. Retrieved 3 August 2012.
  30. ^ Lewis Van Hagen Judson; United States. National Bureau of Standards (1976). Weights and measures standards of the United States: a brief history. Dept. of Commerce, National Bureau of Standards : for sale by the Supt. of Docs., U.S. Govt. Print. Off. pp. 30–1. Retrieved 16 September 2012.
  31. ^ Statutory Rule No. 142.
  32. ^ Australian Government ComLaw Weights and Measures (National Standards) Regulations - C2004L00578
  33. ^ Weights and Measures Act of 1963.
  34. ^ "Thoburn v Sunderland City Council [2002] EWHC 195 (Admin)". England and Wales High Court. 18 February 2002 – via British and Irish Legal Information Institute.
  35. ^ "On what basis is one inch exactly equal to 25.4 mm? Has the imperial inch been adjusted to give this exact fit and if so when?". National Physical Laboratory. 25 March 2010. Retrieved 5 April 2013.
  36. ^ A. V. Astin & H. Arnold Karo, (1959), Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, 30 June 1959, 8:45 am)
  37. ^ "Dictionary of the Scots Language". Edinburgh: Scottish Language Dictionaries. Retrieved 21 May 2011.
  38. ^ Heywood, John (1546). A dialogue conteinying the nomber in effect of all the prouerbes in the englishe tongue, compacte in a matter concernyng two maner of mariages, etc. London: Thomas Berthelet. Full text of 1874 reprint
  39. ^ Gibson, A. J. S.; Smout, T. C. (19 July 2007). Prices, Food and Wages in Scotland, 1550-1780. Cambridge University Press. p. 371. ISBN 978-0-521-03780-8. Retrieved 11 March 2012.
  40. ^ "give someone an inch (and they'll take a mile / yard )". Macmillan Dictionary. Retrieved 28 March 2017.


  • Attenborough, F. L. (1922), The Laws of the Earliest English Kings (Llanerch Press Facsimile Reprint 2000 ed.), Cambridge: Cambridge University Press, ISBN 978-1-86143-101-1, retrieved 11 July 2018
  • Collins Encyclopedia of Scotland
  • Weights and Measures, by D. Richard Torrance, SAFHS, Edinburgh, 1996, ISBN 1-874722-09-9 (NB book focusses on Scottish weights and measures exclusively)
  • This article incorporates text from "Dwelly's [Scottish] Gaelic Dictionary" (1911).
  • Scottish National Dictionary and Dictionary of the Older Scottish Tongue
CD single

A CD single (sometimes abbreviated to CDS) is a music single in the form of a compact disc. The standard in the Red Book for the term CD single is an 8cm (3 inch) CD (or Mini CD). It now refers to any single recorded onto a CD of any size, particularly the CD5, or 5-inch CD single. The format was introduced in the mid-1980s but did not gain its place in the market until the early 1990s. With the rise in digital downloads in the early 2010s, sales of CD singles have decreased.

Commercially released CD singles can vary in length from two songs (an A side and B side, in the tradition of 7" 45rpm records) up to six songs like an EP. Some contain multiple mixes of one or more songs (known as remixes), in the tradition of 12" vinyl singles, and in some cases, they may also contain a music video for the single itself as well as a collectible poster. Depending on the nation, there may be limits on the number of songs and total length for sales to count in singles charts.


In guns, particularly firearms, caliber or calibre is the specified nominal internal diameter of the gun barrel bore regardless of how or where the bore is measured and whether or not the finished bore matches that specification It is measured in inches to an accuracy of hundredths or thousandths of an inch or in millimetres. For example, a ".45 caliber" firearm has a barrel diameter of roughly 0.45 inches (11 mm). Barrel diameters can also be expressed using metric dimensions. For example, a "9 mm pistol" has a barrel diameter of about 9 millimeters. Due to the inaccuracy and imprecision of imperial dimensions "converted" to metric units, metric designations are typically far out of specifications published in decimal inches. True "caliber" specifications require imperial measure, and even when cartridge designations (often mistakenly referred to as "caliber") only specify caliber to even tenths or hundredths of an inch, actual barrel/chamber/projectile dimensions are published to at least thousandths of an inch and frequently tolerances extend into ten-thousandths of an inch.

In a rifled barrel, the distance is measured between opposing lands or grooves; groove measurements are common in cartridge designations originating in the United States, while land measurements are more common elsewhere in the world. Measurements "across the grooves" are used for maximum precision because rifling and the specific caliber so-measured is the result of final machining process which cuts grooves into the rough bore leaving the "lands" behind.

Good performance requires a concentric, straight bore that accurately centers the projectile within in preference to a "tight" fit which can be achieved even with off-center, crooked bores that cause excessive friction, fouling and an out-of-balance, wobbling projectile in flight.

While modern firearms are generally referred to by the name of the cartridge the gun is chambered for, they are still categorized together based on bore diameter. For example, a firearm might be described as a "30 caliber rifle", which could be any of a wide range of cartridges using a roughly 0.30 inches (7.6 mm) projectile; or a "22 rimfire", referring to any rimfire firearms firing cartridges with a .22 caliber projectile. However, there can be significant differences in nominal bullet and bore dimensions and all cartridges so "categorized" are not automatically identical in actual caliber.

For example, .303 British firearms and projectiles are often "categorized" as ".30-caliber" alongside several dozen U.S. ".30-caliber" cartridges despite using bullets .310-.312" diameter while all U.S ".30-caliber" centerfire rifle cartridges use a common, standard .308" bullet outside diameter. Using bullets larger than design specifications causes excessive pressures while undersize bullets cause low pressures,insufficient muzzle veloties and fouling that will eventually lead to excessive pressures.

Regardless of common practice among "shooters", caliber refers to specific, precise and crucial bore/bullet dimensions and generic categorizations involving "caliber" are of little beneficial to the shooting and arms industries.


The dreadnought was the predominant type of battleship in the early 20th century. The first of its kind, the Royal Navy's HMS Dreadnought, made such a strong impression on people's minds when launched in 1906 that similar battleships built subsequently were referred to generically as "dreadnoughts", and earlier battleships became known as "pre-dreadnoughts". Dreadnought's design had two revolutionary features: an "all-big-gun" armament scheme, with more heavy-calibre guns than previous ships, and steam turbine propulsion. As dreadnoughts became a symbol of national power, the arrival of these new warships was a crucial catalyst in the intensifying naval arms race between the United Kingdom and Germany. With the launch of a single ship, Dreadnought, the scales of naval power were reset overnight. As a result, dreadnought races sprang up around the world, including in South America, during the lead up to World War I. Successive designs increased rapidly in size and made use of improvements in armament, armour, and propulsion throughout the dreadnought era. Within five years, new battleships had outclassed Dreadnought. These more powerful vessels were known as "super-dreadnoughts". Most of the original dreadnoughts were scrapped after the end of World War I under the terms of the Washington Naval Treaty, but many of the newer super-dreadnoughts continued to be used throughout World War II. The only surviving dreadnought is USS Texas, located near the San Jacinto Battleground State Historic Site.Dreadnought-building consumed vast resources in the early 20th century, but there was only one battle between large dreadnought fleets. In the 1916 Battle of Jutland, the British and German navies clashed with no decisive result. The term "dreadnought" gradually dropped from use after World War I, especially after the Washington Naval Treaty, as virtually all remaining battleships shared dreadnought characteristics; the term can also be used to describe battlecruisers, the other type of ship resulting from the dreadnought revolution.

Extended play

An extended play record, often referred to as an EP, is a musical recording that contains more tracks than a single, but is usually unqualified as an album or LP. Contemporary EPs generally contain a minimum of three tracks and maximum of six tracks, and are considered "less expensive and time-consuming" for an artist to produce than an album. An EP originally referred to specific types of vinyl records other than 78 rpm standard play (SP) and LP, but it is now applied to mid-length CDs and downloads as well.

Ricardo Baca of The Denver Post said, "EPs—originally extended-play 'single' releases that are shorter than traditional albums—have long been popular with punk and indie bands." In the United Kingdom, the Official Chart Company defines a boundary between EP and album classification at 25 minutes of maximum length and no more than four tracks (not counting alternative versions of featured songs, if present).

Floppy disk

A floppy disk, also known as a floppy, diskette, or simply disk, is a type of disk storage composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic enclosure lined with fabric that removes dust particles. Floppy disks are read and written by a floppy disk drive (FDD).

Floppy disks, initially as 8-inch (203 mm) media and later in 5 1⁄4-inch (133 mm) and ​3 1⁄2 inch (90 mm) sizes, were a ubiquitous form of data storage and exchange from the mid-1970s into the first years of the 21st century. By 2006 computers were rarely manufactured with installed floppy disk drives; ​3 1⁄2-inch floppy disks can be used with an external USB floppy disk drive, but USB drives for ​5 1⁄4-inch, 8-inch, and non-standard diskettes are rare to non-existent. These formats are usually handled by older equipment.

The prevalence of floppy disks in late-twentieth century culture was such that many electronic and software programs still use the floppy disks as save icons. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have been superseded by data storage methods with much greater capacity, such as USB flash drives, flash storage cards, portable external hard disk drives, optical discs, cloud storage and storage available through computer networks.

Hard disk drive

A hard disk drive (HDD), hard disk, hard drive, or fixed disk, is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced (exabytes per year) for servers. Though production is growing slowly, sales revenues and unit shipments are declining because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, better reliability, and much lower latency and access times.The revenues for SSDs, most of which use NAND, slightly exceed those for HDDs. Though SSDs have nearly 10 times higher cost per bit, they are replacing HDDs in applications where speed, power consumption, small size, and durability are important.The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Also there is confusion regarding storage capacity, since capacities are stated in decimal Gigabytes (powers of 10) by HDD manufacturers, whereas some operating systems report capacities in binary Gibibytes, which results in a smaller number than advertised. Performance is specified by the time required to move the heads to a track or cylinder (average access time) adding the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally the speed at which the data is transmitted (data rate).

The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables.


iPad ( EYE-pad) is a line of tablet computers designed, developed and marketed by Apple Inc., which run the iOS mobile operating system. The first iPad was released on April 3, 2010; the most recent iPad models are the iPad (2018), released on March 27, 2018; the fifth-generation iPad mini, released on March 18, 2019; the third-generation iPad Air, released on March 18, 2019; and the 11-inch (280 mm) and third-generation 12.9-inch (330 mm) iPad Pro, released on November 7, 2018.

As of May 2017, Apple has sold more than 360 million iPads, though sales peaked in 2013. It is the most popular tablet computer by sales as of the second quarter of 2018.The user interface is built around the device's multi-touch screen, including a virtual keyboard. All iPads can connect via Wi-Fi; some models also have cellular connectivity. iPads can shoot video, take photos, play music, and perform Internet functions such as web-browsing and emailing. Other functions – games, reference, GPS navigation, social networking, etc. – can be enabled by downloading and installing apps. As of March 2016, the App Store has more than million apps for the iPad by Apple and third parties.

There have been eight versions of the iPad. The first generation established design precedents, some of which have persisted through all models. The 2nd-generation iPad (iPad 2) introduced a new thinner design, a dual-core Apple A5 processor, and VGA front-facing and 720p rear-facing cameras designed for FaceTime video calling. The third generation added a Retina Display, the new Apple A5X processor with a quad-core graphics processor, a 5-megapixel camera, HD 1080p video recording, voice dictation, and 4G (LTE). The fourth generation added the Apple A6X processor and replaced the 30-pin connector with an all-digital Lightning connector. The iPad Air added the Apple A7 processor and the Apple M7 motion coprocessor, and reduced the thickness for the first time since the iPad 2. The iPad Air 2 added the Apple A8X processor, the Apple M8 motion coprocessor, an 8-megapixel camera, and the Touch ID fingerprint sensor; and further reduced the thickness. The iPad introduced in 2017 added the Apple A9 processor, while sacrificing some of the improvements the iPad Air 2 introduced in exchange for a lower launch price.

There have been five versions of the iPad Mini, all of which have a screen size of 7.9 inches (20 cm). The first generation has similar internal specifications to the iPad 2 but uses the Lightning connector instead. The iPad Mini 2 added the Retina Display, the Apple A7 processor, and the Apple M7 motion coprocessor, closely matching the internal specifications of the iPad Air. The iPad Mini 3 added the Touch ID fingerprint sensor. The iPad Mini 4 features the Apple A8 and the Apple M8 motion coprocessor. The 5th generation features the Apple A12 SoC.

There have been three generations of the iPad Pro. The first generation came with 9.7" and 12.9" screen sizes, while the second came with 10.5" and 12.9" sizes, and the third with 11" and 12.9" sizes. The iPad Pros have unique features such as the Smart Connector, which are exclusive to this series of iPads.

IPad Pro

The iPad Pro family is a line of iPad tablet computers designed, developed, and marketed by Apple Inc., that runs the iOS mobile operating system. Its current generation is available in two screen sizes, 11-inch (28 cm) and 12.9-inch (33 cm), each with four options for internal storage capacities: 64, 256, 512 GB, or 1 TB.

The first iPad Pro, the 12.9-inch version, was announced on September 9, 2015 and released on November 11, 2015. It is larger than all previous iPad models and the first iPad tablet to feature LPDDR4 RAM. The 12.9-inch tablet was later followed by the smaller 9.7-inch version, which was announced on March 21, 2016, and released on March 31 that same year.On June 5, 2017, the second generation iPad Pro was announced, which features A10X Fusion processors, with basic storage of 64 GB, and optional 512 GB. Upgraded displays include a new 10.5-inch version to replace the 9.7-inch model, while the 12.9-inch version was refreshed. Following this announcement, both models of the first generation iPad Pro were discontinued.

The third generation of iPad Pro was announced on October 30, 2018. It is available in two screen sizes: 11-inch (28 cm) and 12.9-inch (33 cm). They feature full screen displays, with the 11-inch model replacing the 10.5-inch model of the previous generation. They also feature up to 1 TB of storage and Face ID which works in both vertical and horizontal orientations, a feature that does not apply to iPhones with Face ID. The third generation does not feature a home button.

Inch of mercury

Inch of mercury (inHg and ″Hg) is a unit of measurement for pressure. It is still used for barometric pressure in weather reports, refrigeration and aviation in the United States.

It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity. Conversion to metric units depends on the temperature of mercury, and hence its density; typical conversion factors are:

In older literature, an "inch of mercury" is based on the height of a column of mercury at 60 °F (15.6 °C).

1 inHg60 °F = 3376.85 PaIn English units: 1 inHg60 °F = 0.489 771 psi, or 2.041 771 inHg60 °F = 1 psi.

LP record

The LP (from "long playing" or "long play") is an analog sound storage medium, a vinyl record format characterized by a speed of ​33 1⁄3 rpm, a 12- or 10-inch (30- or 25-cm) diameter, and use of the "microgroove" groove specification. Introduced by Columbia in 1948, it was soon adopted as a new standard by the entire record industry. Apart from a few relatively minor refinements and the important later addition of stereophonic sound, it has remained the standard format for vinyl albums.

MacBook Pro

The MacBook Pro (sometimes abbreviated as MBP) is a line of Macintosh portable computers introduced in January 2006 by Apple Inc. It is the high-end model of the MacBook family and is currently available in 13- and 15-inch screen sizes. A 17-inch version was available between April 2006 and June 2012.

The first generation MacBook Pro is externally similar to the PowerBook G4 it replaces, but uses Intel Core processors instead of PowerPC G4 chips. The 15-inch model was introduced first, in January 2006; the 17-inch model followed in April. Both received several updates and Core 2 Duo processors later in 2006.

The product's second iteration, known as the "unibody" model, has a casing made from a single piece of aluminum. It debuted in October 2008 in 13- and 15-inch screen sizes. In January 2009, the 17-inch model was updated with the same unibody design. Subsequent updates brought upgraded Intel Core i5 and i7 processors and introduced Intel's Thunderbolt technology.

Apple released the third generation of MacBook Pro with a 15-inch screen during WWDC 2012 and discontinued the 17-inch variant. The previous generation 13- and 15-inch unibody models continued to sell with updated processors. The third generation model is thinner than its predecessor and is the first to include a high-resolution Retina Display. A 13-inch variant was released in October 2012.

The fourth generation MacBook Pro was announced on October 27, 2016. This generation replaced all data ports with USB-C, and with the exception of the baseline model, replaced the function keys with an interactive touchscreen strip called the "Touch Bar" with a Touch ID sensor integrated into the Power button.

Nine Inch Nails

Nine Inch Nails, commonly abbreviated as NIN (stylized as NIИ), is an American industrial rock band formed in Cleveland, Ohio in 1988. The band consists of producer and multi-instrumentalist Trent Reznor, as well as English musician Atticus Ross. Over the course of their three-decade existence, the band has signed with several major labels, the most current being Capitol Records, under the name The Null Corporation.

The origins of the band date back to 1988, while Reznor was employed as a janitor at a studio in Cleveland. Utilizing off-hour sessions, Reznor recorded and released the band's debut album, the synth-pop oriented Pretty Hate Machine (1989), under TVT Records to minor success. However, Reznor feuded with the label about promotion. While attempting to terminate his contract, Reznor signed with Interscope Records and released the extended play Broken (1992), a release that diverged significantly from the sound of their debut. Their second and third albums, The Downward Spiral (1994) and The Fragile (1999), were released to critical acclaim and commercial success, bringing the band massive popularity, before going on hiatus. The band resumed touring in 2005 and released their fourth album, With Teeth (2005), to further success. Following the release of their fifth album, Year Zero (2007), Reznor left Interscope over a dispute of physical copies of the album. The band continued touring and independently released their sixth and seventh albums, Ghosts I-IV (2008) and The Slip (2008), before going on hiatus a second time. Returning in 2013, the band released their eighth album, Hesitation Marks (2013), under Columbia Records, followed by a trilogy of releases spanning from 2016-2018, including the EPs Not The Actual Events (2016) and Add Violence (2017), as well as their ninth album, Bad Witch (2018).

Prior to 2016, Reznor was considered the only constant member and creative force of the band, acting as its founder, lead singer, producer, and multi-instrumentalist. In December 2016, English musician Atticus Ross, a frequent collaborator with Reznor, was introduced as a permanent member of Nine Inch Nails. Furthermore, Reznor typically assembles a live band to perform with him onstage. The touring band has comprised several lineups over the course of three decades, the current of which is composed of Robin Finck, Alessandro Cortini, and Ilan Rubin. Their tours often employ thematic visual elements to accompany on-stage performances, which frequently include elaborate light shows, and songs are often rearranged to fit a live setting.

In addition to sales of over 20 million records worldwide, Nine Inch Nails have been nominated for thirteen Grammy Awards, winning twice for the songs "Wish" and "Happiness in Slavery" in 1992 and 1996, respectively. In 1997, Reznor appeared in Time magazine's list of the year's most influential people, and Spin magazine has described him as "the most vital artist in music". In 2004, Rolling Stone placed Nine Inch Nails at 94 on the magazine's list of the 100 greatest artists of all time. Nine Inch Nails was named as a nominee for induction into the Rock and Roll Hall of Fame in 2014, its first year of eligibility. The band was nominated again the following year, but was not inducted.

Oerlikon 20 mm cannon

The Oerlikon 20 mm cannon is a series of autocannons, based on an original German 20 mm Becker design that appeared very early in World War I. It was widely produced by Oerlikon Contraves and others, with various models employed by both Allied and Axis forces during World War II, and many versions still in use today.

Phonograph record

A phonograph record (also known as a gramophone record, especially in British English, or record) is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near the periphery and ends near the center of the disc. At first, the discs were commonly made from shellac; starting in the 1950s polyvinyl chloride became common. In recent decades, records have sometimes been called vinyl records, or simply vinyl.

The phonograph disc record was the primary medium used for music reproduction throughout the 20th century. It had co-existed with the phonograph cylinder from the late 1880s and had effectively superseded it by around 1912. Records retained the largest market share even when new formats such as the compact cassette were mass-marketed. By the 1980s, digital media, in the form of the compact disc, had gained a larger market share, and the vinyl record left the mainstream in 1991. Since the 1990s, records continue to be manufactured and sold on a smaller scale, and are especially used by disc jockeys (DJs) and released by artists in mostly dance music genres, and listened to by a growing niche market of audiophiles. The phonograph record has made a notable niche resurgence in the early 21st century – 9.2 million records were sold in the U.S. in 2014, a 260% increase since 2009. Likewise, in the UK sales have increased five-fold from 2009 to 2014.As of 2017, 48 record pressing facilities remain worldwide, 18 in the United States and 30 in other countries. The increased popularity of vinyl has led to the investment in new and modern record-pressing machines. Only two producers of lacquers (acetate discs) remain: Apollo Masters in California, and MDC in Japan.Phonograph records are generally described by their diameter in inches (12-inch, 10-inch, 7-inch), the rotational speed in revolutions per minute (rpm) at which they are played (​8 1⁄3, ​16 2⁄3, ​33 1⁄3, 45, 78), and their time capacity, determined by their diameter and speed (LP [long playing], 12-inch disc, ​33 1⁄3 rpm; SP [single], 10-inch disc, 78 rpm, or 7-inch disc, 45 rpm; EP [extended play], 12-inch disc or 7-inch disc, ​33 1⁄3 or 45 rpm); their reproductive quality, or level of fidelity (high-fidelity, orthophonic, full-range, etc.); and the number of audio channels (mono, stereo, quad, etc.).

Vinyl records may be scratched or warped if stored incorrectly but if they are not exposed to high heat, carelessly handled or broken, a vinyl record has the potential to last for centuries.The large cover (and inner sleeves) are valued by collectors and artists for the space given for visual expression, especially when it comes to the long play vinyl LP.

Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m2.

Pounds per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi, this will be added to any pressure reading made in air at sea level. The converse is pounds per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psia) will have a pressure of 79.7 psia (14.7 psi + 65 psi). When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).

Service star

A service star is a miniature bronze or silver five-pointed star ​3⁄16 inch (4.8 mm) in diameter that is authorized to be worn by members of the seven uniformed services of the United States on medals and ribbons to denote an additional award or service period. The service star may also be referred to as a campaign star or battle star depending on which award is authorized the star and the manner in which the device is used for the award.Service stars, campaign stars, and battle stars are worn with one point of the star pointing up on the suspension ribbon of a medal or service ribbon. A silver star is worn instead of five bronze stars. A service star is sometimes mistaken for a Bronze Star (Bronze Star Medal) or Silver Star (Silver Star Medal). The service star is also similar to the gold and silver ​5⁄16 Inch Stars which may be authorized to be worn on specific individual decorations of certain services to denote additional decorations.

Single (music)

In the music industry, a single is a type of release, typically a song recording of fewer tracks than an LP record or an album. This can be released for sale to the public in a variety of different formats. In most cases, a single is a song that is released separately from an album, although it usually also appears on an album. Typically, these are the songs from albums that are released separately for promotional uses such as digital download or commercial radio airplay and are expected to be the most popular. In other cases a recording released as a single may not appear on an album.

Despite being referred to as a single, singles can include up to as many as three tracks. The biggest digital music distributor, iTunes Store, accepts as many as three tracks less than ten minutes each as a single, as does popular music player Spotify. Any more than three tracks on a musical release or thirty minutes in total running time is either an extended play (EP) or, if over six tracks long, an album.

Historically, when mainstream music was purchased via vinyl records, singles would be released double-sided. That is to say, they were released with an A-side and B-side, on which two singles would be released, one on each side. Moreover, traditionally, only the most popular songs from a previously released album would be released as a single. In more contemporary forms of music consumption, artists release most, if not all, of the tracks on an album as singles.

Trent Reznor

Michael Trent Reznor (born May 17, 1965) is an American singer, songwriter, musician, record producer, and film score composer. He is the founder, lead vocalist, and principal songwriter of the industrial rock band Nine Inch Nails, which he founded in 1988 and of which he was the sole official member until adding long-time collaborator Atticus Ross as a permanent member in 2016. His first release under the Nine Inch Nails name, the 1989 album Pretty Hate Machine, was a commercial and critical success. He has since released nine Nine Inch Nails studio albums. He left Interscope Records in 2007 and was an independent recording artist until signing with Columbia Records in 2012.

Reznor was associated with the bands Option 30, The Urge, The Innocent, and Exotic Birds in the mid-1980s. Outside of Nine Inch Nails, he has contributed to the albums of artists such as Marilyn Manson and Saul Williams. He and his wife, Mariqueen Maandig, are members of the post-industrial group How to Destroy Angels, with Atticus Ross and long-time Nine Inch Nails graphic designer Rob Sheridan.Reznor and Ross scored the David Fincher films The Social Network (2010), The Girl with the Dragon Tattoo (2011), and Gone Girl (2014), winning the Academy Award for Best Original Score for The Social Network and the Grammy Award for Best Score Soundtrack for Visual Media for The Girl with the Dragon Tattoo. They also scored the 2018 film Bird Box. In 1997, Reznor appeared in Time's list of the year's most influential people, and Spin magazine described him as "the most vital artist in music".

Twelve-inch single

The twelve-inch single (often simply called a 12-inch or 12″) is a type of gramophone record that has wider groove spacing and shorter playing time compared to LPs. This allows for louder levels to be cut on the disc by the mastering engineer, which in turn gives a wider dynamic range, and thus better sound quality. This record type is commonly used in disco and dance music genres, where DJs use them to play in clubs. They are played at either ​33 1⁄3 or 45 rpm.

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