title: Handball content: automatically switch on ball turnover. They physically exchange their positions approximately every 10 minutes (long exchange), and change sides every five minutes (short exchange). The IHF defines 18 hand signals for quick visual communication with players and officials. The signal for warning or disqualification is accompanied by a yellow or red card, respectively. The referees also use whistle blows to indicate infractions or to restart the play. The referees are supported by a "scorekeeper" and a "timekeeper" who attend to formal things such as keeping track of goals and suspensions, or starting and stopping the clock, respectively. They also keep


title: Handball content: an eye on the benches and notify the referees on substitution errors. Their desk is located between the two substitution areas. Each team consists of seven players on court and seven substitute players on the bench. One player on the court must be the designated goalkeeper, differing in his clothing from the rest of the field players. Substitution of players can be done in any number and at any time during game play. An exchange takes place over the substitution line. A prior notification of the referees is not necessary. Some national bodies, such as the Deutsche Handball Bund (DHB,


title: Handball content: "German Handball Federation"), allow substitution in junior teams only when in ball possession or during timeouts. This restriction is intended to prevent early specialization of players to offence or defence. Field players are allowed to touch the ball with any part of their bodies above and including the knee. As in several other team sports, a distinction is made between catching and dribbling. A player who is in possession of the ball may stand stationary for only three seconds, and may take only three steps. They must then either shoot, pass, or dribble the ball. Taking more than three steps


title: Handball content: at any time is considered travelling, and results in a turnover. A player may dribble as many times as they want (though, since passing is faster, it is the preferred method of attack), as long as during each dribble the hand contacts only the top of the ball. Therefore, carrying is completely prohibited, and results in a turnover. After the dribble is picked up, the player has the right to another three seconds or three steps. The ball must then be passed or shot, as further holding or dribbling will result in a "double dribble" turnover and a free throw


title: Handball content: for the other team. Other offensive infractions that result in a turnover include charging and setting an illegal screen. Carrying the ball into the six-meter zone results either in ball possession by the goalkeeper (by attacker) or turnover (by defender). Only the goalkeepers are allowed to move freely within the goal perimeter, although they may not cross the goal perimeter line while carrying or dribbling the ball. Within the zone, they are allowed to touch the ball with all parts of their bodies, including their feet, with a defensive aim (for other actions, they are subject to the same restrictions


title: Handball content: as the field players). The goalkeepers may participate in the normal play of their teammates. They may be substituted by a regular field player if their team elects to use this scheme in order to outnumber the defending players. Earlier, this field player become the designated goalkeeper on the court; and had to wear some vest or bib to be identified as such. That shirt had to be equal in colour and form to the goalkeeper's shirt, to avoid confusion. A rule change meant to make the game more offensive now allows any player to substitute with the goalkeeper. The


title: Handball content: new rule resembles the one used in ice hockey. This rule was first used in the women's world championship in December 2015 and has since been used by the men's European championship in January 2016 and by both genders in the Olympic tournament in Rio in 2016. If either goalkeeper deflects the ball over the outer goal line, their team stays in possession of the ball, in contrast to other sports like football. The goalkeeper resumes the play with a throw from within the zone ("goalkeeper throw"). Passing to one's own goalkeeper results in a turnover. In a penalty shot,


title: Handball content: throwing the ball against the head of a goalkeeper who is not moving risks a direct disqualification ("red card"). Outside of own D-zone, the goalkeeper is treated as a current field player, and has to follow field players' rules; holding or tackling an opponent player outside the area risks a direct disqualification. The goalkeeper may not return to the area with the ball. Each team is allowed to have a maximum of four team officials seated on the benches. An official is anybody who is neither player nor substitute. One official must be the designated representative who is usually the


title: Handball content: team manager. Since 2012, representatives can call up to 3 team timeouts (up to twice per half), and may address the scorekeeper, timekeeper, and referees (before that, it was once per half); overtime and shootouts are considered extensions of the second half. Other officials typically include physicians or managers. Neither official is allowed to enter the playing court without the permission of the referees. The ball is spherical and must be made either of leather or a synthetic material. It is not allowed to have a shiny or slippery surface. As the ball is intended to be operated by a


title: Handball content: single hand, its official sizes vary depending on age and gender of the participating teams. The referees may award a special throw to a team. This usually happens after certain events such as scored goals, off-court balls, turnovers and timeouts. All of these special throws require the thrower to obtain a certain position, and pose restrictions on the positions of all other players. Sometimes the execution must wait for a whistle blow by the referee. Penalties are given to players, in progressive format, for fouls that require more punishment than just a free-throw. Actions directed mainly at the opponent and


title: Handball content: not the ball (such as reaching around, holding, pushing, tripping, and jumping into opponent) as well as contact from the side, from behind a player or impeding the opponent's counterattack are all considered illegal and are subject to penalty. Any infraction that prevents a clear scoring opportunity will result in a seven-meter penalty shot. Typically the referee will give a warning yellow card for an illegal action; but, if the contact was particularly dangerous, like striking the opponent in the head, neck or throat, the referee can forego the warning for an immediate two-minute suspension. A player can get only


title: Handball content: one warning before receiving a two-minute suspension. One player is only permitted two two-minute suspensions; after the third time, they will be shown the red card. A red card results in an ejection from the game and a two-minute penalty for the team. A player may receive a red card directly for particularly rough penalties. For instance, any contact from behind during a fast break is now being treated with a red card. A red-carded player has to leave the playing area completely. A player who is disqualified may be substituted with another player after the two-minute penalty is served.


title: Handball content: A coach or official can also be penalized progressively. Any coach or official who receives a two-minute suspension will have to pull out one of their players for two minutes; however, the player is not the one punished, and can be substituted in again, as the penalty consists of the team playing with a one player less than the opposing team. After referees award the ball to the opponents for whatever reason, the player currently in possession of the ball has to lay it down quickly, or risk a two-minute suspension. Also, gesticulating or verbally questioning the referee's order, as


title: Handball content: well as arguing with the officials' decisions, will normally result in a two-minute suspension. If the suspended player protests further, does not walk straight off the field to the bench, or if the referee deems the tempo deliberately slow, the player can be given an additional two-minute suspension. Illegal substitution (outside of the dedicated area, or if the replacement player enters too early) is also punishable by a two-minute suspension. Players are typically referred to by the positions they are playing. The positions are always denoted from the view of the respective goalkeeper, so that a defender on the right


title: Handball content: opposes an attacker on the left. However, not all of the following positions may be occupied depending on the formation or potential suspensions. Sometimes, the offense uses formations with two pivot players. There are many variations in defensive formations. Usually, they are described as "n:m" formations, where "n" is the number of players defending at the goal line and "m" the number of players defending more offensive. Exceptions are the 3:2:1 defense and n+m formation (e.g. 5+1), where m players defend some offensive player in man coverage (instead of the usual zone coverage). Attacks are played with all field players


title: Handball content: on the side of the defenders. Depending on the speed of the attack, one distinguishes between three attack "waves" with a decreasing chance of success: The third wave evolves into the normal offensive play when all defenders not only reach the zone, but gain their accustomed positions. Some teams then substitute specialised offence players. However, this implies that these players must play in the defence should the opposing team be able to switch quickly to offence. The latter is another benefit for fast playing teams. If the attacking team does not make sufficient progress (eventually releasing a shot on goal),


title: Handball content: the referees can call passive play (since about 1995, the referee gives a passive warning some time before the actual call by holding one hand up in the air, signalling that the attacking team should release a shot soon), turning control over to the other team. A shot on goal or an infringement leading to a yellow card or two-minute penalty will mark the start of a new attack, causing the hand to be taken down; but a shot blocked by the defense or a normal free throw will not. If it were not for this rule, it would be


title: Handball content: easy for an attacking team to stall the game indefinitely, as it is difficult to intercept a pass without at the same time conceding dangerous openings towards the goal. The usual formations of the defense are 6–0, when all the defense players line up between the and lines to form a wall; the 5–1, when one of the players cruises outside the perimeter, usually targeting the center forwards while the other 5 line up on the line; and the less common 4–2 when there are two such defenders out front. Very fast teams will also try a 3–3 formation which


title: Handball content: is close to a switching man-to-man style. The formations vary greatly from country to country, and reflect each country's style of play. 6–0 is sometimes known as "flat defense", and all other formations are usually called "offensive defense". Handball teams are usually organised as clubs. On a national level, the clubs are associated in federations which organize matches in leagues and tournaments. The International Handball Federation (IHF) is the administrative and controlling body for international handball. Handball is an Olympic sport played during the Summer Olympics. The IHF organizes world championships, held in odd-numbered years, with separate competitions for men


title: Handball content: and women. The IHF World Men's Handball Championship 2017 title holders are France. The IHF 2017 Women's World Championship title holders are also France. The IHF is composed of five continental federations: Asian Handball Federation, African Handball Confederation, Pan-American Team Handball Federation, European Handball Federation and Oceania Handball Federation. These federations organize continental championships held every other second year. Handball is played during the Pan American Games, All-Africa Games, and Asian Games. It is also played at the Mediterranean Games. In addition to continental competitions between national teams, the federations arrange international tournaments between club teams. The current worldwide attendance


title: Handball content: record for seven-a-side handball was set on September 6, 2014, during a neutral venue German league game between HSV Hamburg and the Mannheim-based Rhein-Neckar Lions. The matchup drew 44,189 spectators to Commerzbank Arena in Frankfurt, exceeding the previous record of 36,651 set at Copenhagen's Parken Stadium during the 2011 Danish Cup final. Handball events have been selected as a main motif in numerous collectors' coins. One of the recent samples is the €10 Greek Handball commemorative coin, minted in 2003 to commemorate the 2004 Summer Olympics. On the coin, the modern athlete directs the ball in his hands towards his


title: Handball content: target, while in the background the ancient athlete is just about to throw a ball, in a game known as cheirosphaira, in a representation taken from a black-figure pottery vase of the Archaic period. The most recent commemorative coin featuring handball is the British 50 pence coin, part of the series of coins commemorating the London 2012 Olympic Games. Notes Contributor: The Editors of Encyclopædia Britannica Article Title: Team handball Website Name: Encyclopædia Britannica Publisher: Encyclopædia Britannica, inc. Date Published: May 3, 2017 URL: https://www.britannica.com/sports/team-handball Handball Handball (also known as team handball, fieldball, European handball or Olympic handball) is a


title: "History of physics" content: in coordination with English scientist Robert Hooke, built an air pump. Using this pump, Boyle and Hooke noticed the pressure-volume correlation for a gas: "PV" = "k", where "P" is pressure, "V" is volume and "k" is a constant: this relationship is known as Boyle's Law. In that time, air was assumed to be a system of motionless particles, and not interpreted as a system of moving molecules. The concept of thermal motion came two centuries later. Therefore, Boyle's publication in 1660 speaks about a mechanical concept: the air spring. Later, after the invention of the thermometer, the property temperature


title: "Military of Honduras" content: a justification and cause for acquittal that will protect us." He said the decision was taken by the military leadership "in order to avoid bloodshed". Following the 2009 ouster of the president, the Honduran military together with other government security forces were allegedly responsible for thousands of allegedly arbitrary detentions and for several forced disappearances and extrajudicial executions of opponents to the "de facto" government, including members of the Democratic Unification Party. However, evidence about these actions has yet to be provided and there has been some questioning in local media about the actual perpetrators, suggesting that they could actually


title: "Howland Island" content: his ship's owners on December 1, 1828. Howland Island was at last named on September 9, 1842 after a lookout who sighted it from the whaleship "Isabella" under Captain Geo. E. Netcher of New Bedford. Howland Island was uninhabited when the United States took possession of it under the Guano Islands Act of 1856. The island was a known navigation hazard for many decades and several ships were wrecked there. Its guano deposits were mined by American companies from about 1857 until October 1878, although not without controversy. Captain Geo. E. Netcher of the "Isabella" informed Captain Taylor of its


title: Hamburg content: industrial rock band KMFDM was also formed in Hamburg, initially as a performance art project. The influences of these and other bands from the area helped establish the subgenre of power metal. Hamburg has a vibrant psychedelic trance community, with record labels such as Spirit Zone. Hamburg is noted for several festivals and regular events. Some of them are street festivals, such as the gay pride "Hamburg Pride" festival or the Alster fair (German: "Alstervergnügen"), held at the "Binnenalster". The "Hamburger DOM" is northern Germany's biggest funfair, held three times a year. "Hafengeburtstag" is a funfair to honour the birthday


title: "Heathrow Airport" content: the commission backed a third runway at Heathrow, which the government approved in October 2016. Heathrow is west of central London, near the south end of the London Borough of Hillingdon on a parcel of land that is designated part of the Metropolitan Green Belt. The airport is surrounded by the villages of Harlington, Harmondsworth, Longford and Cranford to the north and by Hounslow and Hatton to the east. To the south lie Bedfont and Stanwell while to the west Heathrow is separated from Slough in Berkshire by the M25 motorway. Heathrow falls entirely under the Twickenham postcode area, with


title: "Hexen: Beyond Heretic" content: played in low detail mode. Due to cartridge storage limitations, the Nintendo 64 version is based on the original PC floppy version and lacks the FMV scenes and Redbook audio music introduced in the CD-ROM version, although it has new narrative introductions to the levels. "Deathkings of the Dark Citadel" is an official expansion pack that was released for "Hexen" in 1996. It features three more hubs with a total of 20 new single player levels and six new deathmatch levels. Unlike the "Shadow of the Serpent Riders" expansion pack for "Heretic", it had to be purchased in retail stores


title: "Herman Melville" content: upon no source, and his prose is not based on anybody else's verse but on an awareness of "speech rhythm". Melville's mastering of Shakespeare, Matthiessen finds, supplied him with verbal resources that enabled him to create dramatic language through three essential techniques. First, the use of verbs of action creates a sense of movement and meaning. The effective tension caused by the contrast of "thou launchest navies of full-freighted worlds" and "there's that in here that still remains indifferent" in "The Candles" (Ch. 119) makes the last clause lead to a "compulsion to strike the breast," which suggests "how thoroughly


title: "Heat engine" content: Heat engine In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a low temperature state. During this process some of the thermal energy is


title: "Heat engine" content: converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, a lot of heat is lost to the surroundings and so cannot be converted to work. In general an engine converts energy to mechanical work. Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem. Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can


title: "Heat engine" content: be easily converted to heat by processes like exothermic reactions (such as combustion), absorption of light or energetic particles, friction, dissipation and resistance. Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines are very versatile and have a wide range of applicability. Heat engines are often confused with the cycles they attempt to implement. Typically, the term "engine" is used for a physical device and "cycle" for the model. In thermodynamics, heat engines are often modeled using a standard engineering model such as the Otto cycle.


title: "Heat engine" content: The theoretical model can be refined and augmented with actual data from an operating engine, using tools such as an indicator diagram. Since very few actual implementations of heat engines exactly match their underlying thermodynamic cycles, one could say that a thermodynamic cycle is an ideal case of a mechanical engine. In any case, fully understanding an engine and its efficiency requires gaining a good understanding of the (possibly simplified or idealized) theoretical model, the practical nuances of an actual mechanical engine, and the discrepancies between the two. In general terms, the larger the difference in temperature between the hot


title: "Heat engine" content: source and the cold sink, the larger is the potential thermal efficiency of the cycle. On Earth, the cold side of any heat engine is limited to being close to the ambient temperature of the environment, or not much lower than 300 kelvins, so most efforts to improve the thermodynamic efficiencies of various heat engines focus on increasing the temperature of the source, within material limits. The maximum theoretical efficiency of a heat engine (which no engine ever attains) is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, all


title: "Heat engine" content: expressed as absolute temperatures (in kelvins). The efficiency of various heat engines proposed or used today has a large range: All these processes gain their efficiency (or lack thereof) from the temperature drop across them. Significant energy may be used for auxiliary equipment, such as pumps, which effectively reduces efficiency. Heat engines can be characterized by their specific power, which is typically given in kilowatts per litre of engine displacement (in the U.S. also horsepower per cubic inch). The result offers an approximation of the peak power output of an engine. This is not to be confused with fuel efficiency,


title: "Heat engine" content: since high efficiency often requires a lean fuel-air ratio, and thus lower power density. A modern high-performance car engine makes in excess of 75 kW/l (1.65 hp/in). Examples of everyday heat engines include the steam engine and the internal combustion engine. The stirling engine is also heat engine, as well as the drinking bird toy. All of these heat engines are powered by the expansion of heated gases. It is important to note that although some cycles have a typical combustion location (internal or external), they often can be implemented with the other. For example, John Ericsson developed an external


title: "Heat engine" content: heated engine running on a cycle very much like the earlier Diesel cycle. In addition, externally heated engines can often be implemented in open or closed cycles. Earth's atmosphere and hydrosphere—Earth’s heat engine—are coupled processes that constantly even out solar heating imbalances through evaporation of surface water, convection, rainfall, winds, and ocean circulation, when distributing heat around the globe. The Hadley system provides an example of a heat engine. The Hadley circulation is identified with rising of warm and moist air in the equatorial region with descent of colder air in the subtropics corresponding to a thermally driven direct circulation,


title: "Heat engine" content: with consequent net production of kinetic energy. In these cycles and engines, the working fluids are gases and liquids. The engine converts the working fluid from a gas to a liquid, from liquid to gas, or both, generating work from the fluid expansion or compression. In these cycles and engines the working fluid is always a gas (i.e., there is no phase change): In these cycles and engines the working fluid are always like liquid: A domestic refrigerator is an example of a heat pump: a heat engine in reverse. Work is used to create a heat differential. Many cycles


title: "Heat engine" content: can run in reverse to move heat from the cold side to the hot side, making the cold side cooler and the hot side hotter. Internal combustion engine versions of these cycles are, by their nature, not reversible. Refrigeration cycles include: The Barton evaporation engine is a heat engine based on a cycle producing power and cooled moist air from the evaporation of water into hot dry air. Mesoscopic heat engines are nanoscale devices that may serve the goal of processing heat fluxes and perform useful work at small scales. Potential applications include e.g. electric cooling devices. In such mesoscopic


title: "Heat engine" content: heat engines, work per cycle of operation fluctuates due to thermal noise. There is exact equality that relates average of exponents of work performed by any heat engine and the heat transfer from the hotter heat bath. This relation transforms the Carnot's inequality into exact equality. The efficiency of a heat engine relates how much useful work is output for a given amount of heat energy input. From the laws of thermodynamics, after a completed cycle: In other words, a heat engine absorbs heat energy from the high temperature heat source, converting part of it to useful work and delivering


title: "Heat engine" content: the rest to the cold temperature heat sink. In general, the efficiency of a given heat transfer process (whether it be a refrigerator, a heat pump or an engine) is defined informally by the ratio of "what you get out" to "what you put in". In the case of an engine, one desires to extract work and puts in a heat transfer. The "theoretical" maximum efficiency of any heat engine depends only on the temperatures it operates between. This efficiency is usually derived using an ideal imaginary heat engine such as the Carnot heat engine, although other engines using different


title: "Heat engine" content: cycles can also attain maximum efficiency. Mathematically, this is because in reversible processes, the change in entropy of the cold reservoir is the negative of that of the hot reservoir (i.e., formula_7), keeping the overall change of entropy zero. Thus: where formula_9 is the absolute temperature of the hot source and formula_10 that of the cold sink, usually measured in kelvins. Note that formula_11 is positive while formula_12 is negative; in any reversible work-extracting process, entropy is overall not increased, but rather is moved from a hot (high-entropy) system to a cold (low-entropy one), decreasing the entropy of the heat


title: "Heat engine" content: source and increasing that of the heat sink. The reasoning behind this being the maximal efficiency goes as follows. It is first assumed that if a more efficient heat engine than a Carnot engine is possible, then it could be driven in reverse as a heat pump. Mathematical analysis can be used to show that this assumed combination would result in a net decrease in entropy. Since, by the second law of thermodynamics, this is statistically improbable to the point of exclusion, the Carnot efficiency is a theoretical upper bound on the reliable efficiency of "any" thermodynamic cycle. Empirically, no


title: "Heat engine" content: heat engine has ever been shown to run at a greater efficiency than a Carnot cycle heat engine. Figure 2 and Figure 3 show variations on Carnot cycle efficiency. Figure 2 indicates how efficiency changes with an increase in the heat addition temperature for a constant compressor inlet temperature. Figure 3 indicates how the efficiency changes with an increase in the heat rejection temperature for a constant turbine inlet temperature. The most Carnot efficiency as a criterion of heat engine performance is the fact that by its nature, any maximally efficient Carnot cycle must operate at an infinitesimal temperature gradient.


title: "Heat engine" content: This is because "any" transfer of heat between two bodies at differing temperatures is irreversible, and therefore the Carnot efficiency expression only applies in the infinitesimal limit. The major problem with that is that the object of most heat engines is to output some sort of power, and infinitesimal power is usually not what is being sought. A different measure of ideal heat engine efficiency is given by considerations of endoreversible thermodynamics, where the cycle is identical to the Carnot cycle except in that the two processes of heat transfer are "not" reversible (Callen 1985): This model does a better


title: "Heat engine" content: job of predicting how well real-world heat engines can do (Callen 1985, see also endoreversible thermodynamics): As shown, the endoreversible efficiency much more closely models the observed. Heat engines have been known since antiquity but were only made into useful devices at the time of the industrial revolution in the 18th century. They continue to be developed today. Engineers have studied the various heat engine cycles extensively in effort to improve the amount of usable work they could extract from a given power source. The Carnot cycle limit cannot be reached with any gas-based cycle, but engineers have worked out


title: "Heat engine" content: at least two ways to possibly go around that limit, and one way to get better efficiency without bending any rules. Each process is one of the following: Heat engine In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the


title: "Marrubium vulgare" content: Marrubium vulgare Marrubium vulgare (white horehound or common horehound) is a flowering plant in the mint family (Lamiaceae), native to Europe, northern Africa, and southwestern and central Asia. It is also widely naturalized in many places, including most of North and South America. It is a grey-leaved herbaceous perennial plant, and grows to tall. The leaves are long with a densely crinkled surface, and are covered in downy hairs. The flowers are white, borne in clusters on the upper part of the main stem. The Oxford English Dictionary derives the word from two Old English forms: "hoar" ("white," "light-colored," as


title: "Marrubium vulgare" content: in "hoarfrost") and "hune" a word of unknown origin designating a class of herbs or plants. The second element was altered by folk etymology. Horehound has been mentioned in conjunction with medicinal use dating at least back to the 1st century BC, where it appeared as a remedy for respiratory ailments in the treatise "De Medicina" by Roman encyclopaedist Aulus Cornelius Celsus. The Roman agricultural writer Columella lists it as a remedy for expelling worms in farm animals in his important first-century work "On Agriculture". Since then, horehound has appeared for similar purposes in numerous herbals over the centuries, such


title: "Marrubium vulgare" content: as "The Herball, or, Generall historie of plantes" by John Gerard, and "Every Man His Own Doctor: or, The Poor Planter’s Physician" by Dr. John Tennent. Horehound is used to make hard lozenge candies that are considered by folk medicine to aid digestion, soothe sore throats, and relieve inflammation. It is also used in beverages, such as horehound beer, steeped as tea (similar to the Maghrebi mint tea), and in the rock and rye cocktail. Horehound was introduced to southern Australia in the 19th century as a medicinal herb. It became a weed of native grasslands and pastures where it


title: "Marrubium vulgare" content: was introduced with settlers’ livestock, and was first declared under noxious weeds legislation. It now appears to have reached its full potential distribution. It occupies disturbed or overgrazed ground, and is favoured by grazing because it is highly unpalatable to livestock. It may persist in native vegetation that has been grazed. "Marrubium vulgare" is also used as a natural grasshopper repellent in agriculture. According to John Gower in Book 7 of the "Confessio Amantis", this plant was the herb of the fourth star of Nectanebus' astrology, Capella. Gower uses the older name, Alhaiot (VII:1338). Marrubium vulgare Marrubium vulgare (white horehound


title: "Henry Fielding" content: past. Although begun as a parody, it developed into an accomplished novel in its own right and is considered to mark Fielding's debut as a serious novelist. In 1743, he published a novel in the "Miscellanies" volume III (which was the first volume of the Miscellanies): "The Life and Death of Jonathan Wild, the Great", which is sometimes counted as his first, as he almost certainly began it before he wrote "Shamela" and "Joseph Andrews". It is a satire of Walpole that draws a parallel between him and Jonathan Wild, the infamous gang leader and highwayman. He implicitly compares the


title: "Hard disk drive" content: Hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk, is an electromechanical 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


title: "Hard disk drive" content: 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,


title: "Hard disk drive" content: 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 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 : a 1-terabyte (TB) drive has a capacity of gigabytes (GB; where 1 gigabyte = bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by


title: "Hard disk drive" content: the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is specified by the time required to move the heads to a track or cylinder (average access time) plus 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


title: "Hard disk drive" content: systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables. The first production IBM hard disk drive, the 350 disk storage, shipped in 1957 as a component of the IBM 305 RAMAC system. It was approximately the size of two medium-sized refrigerators and stored five million six-bit characters (3.75 megabytes) on a stack of 50 disks. In 1962, the IBM 350 was superseded by the IBM 1301 disk storage unit, which consisted of 50 platters, each about -inch thick and 24 inches in diameter. While the IBM 350 used only


title: "Hard disk drive" content: two read/write heads, the 1301 used an array of heads, one per platter, moving as a single unit. Cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches (about 6 µm) above the platter surface. Motion of the head array depended upon a binary adder system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes. Access time was about a quarter of a second. Also, in 1962, IBM introduced the model 1311 disk drive, which was


title: "Hard disk drive" content: about the size of a washing machine and stored two million characters on a removable disk pack. Users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called "fixed disk" drives. Some high-performance HDDs were manufactured with one head per track (e.g. IBM 2305 in 1970) so that no time was lost physically moving the heads to a track. Known as fixed-head or head-per-track


title: "Hard disk drive" content: disk drives they were very expensive and are no longer in production. In 1973, IBM introduced a new type of HDD code-named "Winchester". Its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to "land" on a special area of the disk surface upon spin-down, "taking off" again when the disk was later powered on. This greatly reduced the cost of the head actuator mechanism, but precluded removing just the disks from the drive as was done with the disk


title: "Hard disk drive" content: packs of the day. Instead, the first models of "Winchester technology" drives featured a removable disk module, which included both the disk pack and the head assembly, leaving the actuator motor in the drive upon removal. Later "Winchester" drives abandoned the removable media concept and returned to non-removable platters. Like the first removable pack drive, the first "Winchester" drives used platters in diameter. A few years later, designers were exploring the possibility that physically smaller platters might offer advantages. Drives with non-removable eight-inch platters appeared, and then drives that used a form factor (a mounting width equivalent to that used


title: "Hard disk drive" content: by contemporary floppy disk drives). The latter were primarily intended for the then-fledgling personal computer (PC) market. As the 1980s began, HDDs were a rare and very expensive additional feature in PCs, but by the late 1980s their cost had been reduced to the point where they were standard on all but the cheapest computers. Most HDDs in the early 1980s were sold to PC end users as an external, add-on subsystem. The subsystem was not sold under the drive manufacturer's name but under the subsystem manufacturer's name such as Corvus Systems and Tallgrass Technologies, or under the PC system


title: "Hard disk drive" content: manufacturer's name such as the Apple ProFile. The IBM PC/XT in 1983 included an internal 10 MB HDD, and soon thereafter internal HDDs proliferated on personal computers. External HDDs remained popular for much longer on the Apple Macintosh. Many Macintosh computers made between 1986 and 1998 featured a SCSI port on the back, making external expansion simple. Older compact Macintosh computers did not have user-accessible hard drive bays (indeed, the Macintosh 128K, Macintosh 512K, and Macintosh Plus did not feature a hard drive bay at all), so on those models external SCSI disks were the only reasonable option for expanding


title: "Hard disk drive" content: upon any internal storage. The 2011 Thailand floods damaged the manufacturing plants and impacted hard disk drive cost adversely between 2011 and 2013. Driven by ever increasing areal density, HDDs have continuously improved; a few highlights are listed in the table above. Market applications expanded through the 2000s, from the mainframe computers of the late 1950s to most mass storage applications including computers and consumer applications such as storage of entertainment content. NAND performance is improving faster than HDDs, and applications for HDDs are eroding. Smaller form factors, 1.8-inches and below, were discontinued around 2010. The price of solid-state storage


title: "Hard disk drive" content: (NAND), represented by Moore's law, is improving faster than HDDs. NAND has a higher price elasticity of demand than HDDs, and this drives market growth. During the late 2000s and 2010s, the product life cycle of HDDs entered a mature phase, and slowing sales may indicate the onset of the declining phase. A modern HDD records data by magnetizing a thin film of ferromagnetic material on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme,


title: "Hard disk drive" content: such as run-length limited encoding, which determines how the data is represented by the magnetic transitions. A typical HDD design consists of a "" that holds flat circular disks, also called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminum alloy, glass, or ceramic. They are coated with a shallow layer of magnetic material typically 10–20 nm in depth, with an outer layer of carbon for protection. For reference, a standard piece of copy paper is thick. The platters in contemporary HDDs are spun at speeds varying from 4,200 rpm in energy-efficient portable


title: "Hard disk drive" content: devices, to 15,000 rpm for high-performance servers. The first HDDs spun at 1,200 rpm and, for many years, 3,600 rpm was the norm. As of December 2013, the platters in most consumer-grade HDDs spin at either 5,400 rpm or 7,200 rpm. Information is written to and read from a platter as it rotates past devices called read-and-write heads that are positioned to operate very close to the magnetic surface, with their flying height often in the range of tens of nanometers. The read-and-write head is used to detect and modify the magnetization of the material passing immediately under it. In


title: "Hard disk drive" content: modern drives, there is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a voice coil actuator or in some older designs a stepper motor. Early hard disk drives wrote data at some constant bits per second, resulting in all tracks having the same amount of data per track but modern drives (since the


title: "Hard disk drive" content: 1990s) use zone bit recording – increasing the write speed from inner to outer zone and thereby storing more data per track in the outer zones. In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects, thermally induced magnetic instability which is commonly known as the "superparamagnetic limit". To counter this, the platters are coated with two parallel magnetic layers, separated by a three-atom layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other. Another technology used


title: "Hard disk drive" content: to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005, and as of 2007 the technology was used in many HDDs. In 2004, a new concept was introduced to allow further increase of the data density in magnetic recording, using recording media consisting of coupled soft and hard magnetic layers. That so-called "exchange spring media", also known as "exchange coupled composite media", allows good writability due to the write-assist nature of the soft layer. However, the thermal stability is determined only by the hardest layer and not influenced by the soft layer. A typical


title: "Hard disk drive" content: HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place. Opposite the actuator at the end of the head support arm is the read-write head; thin printed-circuit cables connect the read-write heads to amplifier electronics mounted at the pivot of the actuator. The head support arm is very light, but also stiff; in modern drives, acceleration at the head reaches 550 "g". The "" is a


title: "Hard disk drive" content: permanent magnet and moving coil motor that swings the heads to the desired position. A metal plate supports a squat neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate is the moving coil, often referred to as the "voice coil" by analogy to the coil in loudspeakers, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives have only one magnet). The voice coil itself is shaped rather like an arrowhead, and made of doubly coated copper magnet wire. The inner layer is insulation, and the outer


title: "Hard disk drive" content: is thermoplastic, which bonds the coil together after it is wound on a form, making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the actuator bearing center) then interact with the magnetic field of the fixed magnet. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the tangential force. If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore, the surface of the magnet is half north pole and half south pole, with the


title: "Hard disk drive" content: radial dividing line in the middle, causing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head. The HDD's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to servo feedback. These are either complete concentric circles (in the case of dedicated


title: "Hard disk drive" content: servo technology), or segments interspersed with real data (in the case of embedded servo technology). The servo feedback optimizes the signal to noise ratio of the GMR sensors by adjusting the voice-coil of the actuated arm. The spinning of the disk also uses a servo motor. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed. Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra


title: "Hard disk drive" content: bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity. For example, a typical 1 TB hard disk with 512-byte sectors provides additional capacity of about 93 GB for the ECC data. In the newest drives, as of 2009, low-density parity-check codes (LDPC) were supplanting Reed–Solomon; LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available. Typical hard disk drives attempt to "remap" the data in a


title: "Hard disk drive" content: physical sector that is failing to a spare physical sector provided by the drive's "spare sector pool" (also called "reserve pool"), while relying on the ECC to recover stored data while the number of errors in a bad sector is still low enough. The S.M.A.R.T (Self-Monitoring, Analysis and Reporting Technology) feature counts the total number of errors in the entire HDD fixed by ECC (although not on all hard drives as the related S.M.A.R.T attributes "Hardware ECC Recovered" and "Soft ECC Correction" are not consistently supported), and the total number of performed sector remappings, as the occurrence of many such


title: "Hard disk drive" content: errors may predict an HDD failure. The "No-ID Format", developed by IBM in the mid-1990s, contains information about which sectors are bad and where remapped sectors have been located. Only a tiny fraction of the detected errors end up as not correctable. Examples of specified uncorrected bit read error rates include: Within a given manufacturers model the uncorrected bit error rate is typically the same regardless of capacity of the drive. The worst type of errors are silent data corruptions which are errors undetected by the disk firmware or the host operating system; some of these errors may be caused


title: "Hard disk drive" content: by hard disk drive malfunctions while others originate elsewhere in the connection between the drive and the host. The rate of areal density advancement was similar to Moore's law (doubling every two years) through 2010: 60% per year during 1988–1996, 100% during 1996–2003 and 30% during 2003–2010. Gordon Moore (1997) called the increase "flabbergasting," while observing later that growth cannot continue forever. Price improvement decelerated to −12% per year during 2010–2017, as the growth of areal density slowed. The rate of advancement for areal density slowed to 10% per year during 2010–2016, and there was difficulty in migrating from perpendicular


title: "Hard disk drive" content: recording to newer technologies. As bit cell size decreases, more data can be put onto a single drive platter. In 2013, a production desktop 3 TB HDD (with four platters) would have had an areal density of about 500 Gbit/in which would have amounted to a bit cell comprising about 18 magnetic grains (11 by 1.6 grains). Since the mid-2000s areal density progress has increasingly been challenged by a superparamagnetic trilemma involving grain size, grain magnetic strength and ability of the head to write. In order to maintain acceptable signal to noise smaller grains are required; smaller grains may self-reverse


title: "Hard disk drive" content: (electrothermal instability) unless their magnetic strength is increased, but known write head materials are unable to generate a magnetic field sufficient to write the medium. Several new magnetic storage technologies are being developed to overcome or at least abate this trilemma and thereby maintain the competitiveness of HDDs with respect to products such as flash memory–based solid-state drives (SSDs). In 2013, Seagate introduced one such technology, shingled magnetic recording (SMR). Additionally, SMR comes with design complexities that may cause reduced write performance. Other new recording technologies that, , still remain under development include heat-assisted magnetic recording (HAMR), microwave-assisted magnetic recording


title: "Hard disk drive" content: (MAMR), two-dimensional magnetic recording (TDMR), bit-patterned recording (BPR), and "current perpendicular to plane" giant magnetoresistance (CPP/GMR) heads. The rate of areal density growth has dropped below the historical Moore's law rate of 40% per year, and the deceleration is expected to persist through at least 2020. Depending upon assumptions on feasibility and timing of these technologies, the median forecast by industry observers and analysts for 2020 and beyond for areal density growth is 20% per year with a range of 10–30%. The achievable limit for the HAMR technology in combination with BPR and SMR may be 10 Tbit/in, which would


title: "Hard disk drive" content: be 20 times higher than the 500 Gbit/in represented by 2013 production desktop HDDs. As of 2015, HAMR HDDs have been delayed several years, and are expected in 2018. They require a different architecture, with redesigned media and read/write heads, new lasers, and new near-field optical transducers. The capacity of a hard disk drive, as reported by an operating system to the end user, is smaller than the amount stated by the manufacturer for several reasons: the operating system using some space, use of some space for data redundancy, and space use for file system structures. Also the difference in


title: "Hard disk drive" content: capacity reported in SI decimal prefixed units vs. binary prefixes can lead to a false impression of missing capacity. Modern hard disk drives appear to their host controller as a contiguous set of logical blocks, and the gross drive capacity is calculated by multiplying the number of blocks by the block size. This information is available from the manufacturer's product specification, and from the drive itself through use of operating system functions that invoke low-level drive commands. The gross capacity of older HDDs is calculated as the product of the number of cylinders per recording zone, the number of bytes


title: "Hard disk drive" content: per sector (most commonly 512), and the count of zones of the drive. Some modern SATA drives also report cylinder-head-sector (CHS) capacities, but these are not physical parameters because the reported values are constrained by historic operating system interfaces. The C/H/S scheme has been replaced by logical block addressing (LBA), a simple linear addressing scheme that locates blocks by an integer index, which starts at LBA 0 for the first block and increments thereafter. When using the C/H/S method to describe modern large drives, the number of heads is often set to 64, although a typical hard disk drive, ,


title: "Hard disk drive" content: has between one and four platters. In modern HDDs, spare capacity for defect management is not included in the published capacity; however, in many early HDDs a certain number of sectors were reserved as spares, thereby reducing the capacity available to the operating system. For RAID subsystems, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID 1 array has about half the total capacity as a result of data mirroring, while a RAID 5 array with drives loses of capacity (which equals to the capacity of a single drive) due to storing parity information. RAID


title: "Hard disk drive" content: subsystems are multiple drives that appear to be one drive or more drives to the user, but provide fault tolerance. Most RAID vendors use checksums to improve data integrity at the block level. Some vendors design systems using HDDs with sectors of 520 bytes to contain 512 bytes of user data and eight checksum bytes, or by using separate 512-byte sectors for the checksum data. Some systems may use hidden partitions for system recovery, reducing the capacity available to the end user. Data is stored on a hard drive in a series of logical blocks. Each block is delimited by


title: "Hard disk drive" content: markers identifying its start and end, error detecting and correcting information, and space between blocks to allow for minor timing variations. These blocks often contained 512 bytes of usable data, but other sizes have been used. As drive density increased, an initiative known as Advanced Format extended the block size to 4096 bytes of usable data, with a resulting significant reduction in the amount of disk space used for block headers, error checking data, and spacing. The process of initializing these logical blocks on the physical disk platters is called "low-level formatting", which is usually performed at the factory and


title: "Hard disk drive" content: is not normally changed in the field. "High-level formatting" writes data structures used by the operating system to organize data files on the disk. This includes writing partition and file system structures into selected logical blocks. For example, some of the disk space will be used to hold a directory of disk file names and a list of logical blocks associated with a particular file. Examples of partition mapping scheme include Master boot record (MBR) and GUID Partition Table (GPT). Examples of data structures stored on disk to retrieve files include the File Allocation Table (FAT) in the DOS file


title: "Hard disk drive" content: system and inodes in many UNIX file systems, as well as other operating system data structures (also known as metadata). As a consequence, not all the space on an HDD is available for user files, but this system overhead is usually small compared with user data. The total capacity of HDDs is given by manufacturers using SI decimal prefixes such as gigabytes (1 GB = 1,000,000,000 bytes) and terabytes (1 TB = 1,000,000,000,000 bytes). This practice dates back to the early days of computing; by the 1970s, "million", "mega" and "M" were consistently used in the decimal sense for drive


title: "Hard disk drive" content: capacity. However, capacities of memory are quoted using a binary interpretation of the prefixes, i.e. using powers of 1024 instead of 1000. Software reports hard disk drive or memory capacity in different forms using either decimal or binary prefixes. The Microsoft Windows family of operating systems uses the binary convention when reporting storage capacity, so an HDD offered by its manufacturer as a 1 TB drive is reported by these operating systems as a 931 GB HDD. Mac OS X 10.6 ("Snow Leopard") uses decimal convention when reporting HDD capacity. The default behavior of the command-line utility on Linux is


title: "Hard disk drive" content: to report the HDD capacity as a number of 1024-byte units. The difference between the decimal and binary prefix interpretation caused some consumer confusion and led to class action suits against HDD manufacturers. The plaintiffs argued that the use of decimal prefixes effectively misled consumers while the defendants denied any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the law and that no class member sustained any damages or injuries. HDD price per byte improved at the rate of −40% per year during 1988–1996, −51% per year during 1996–2003, and −34% per year during


title: "Hard disk drive" content: 2003–2010. The price improvement decelerated to −13% per year during 2011–2014, as areal density increase slowed and the 2011 Thailand floods damaged manufacturing facilities. IBM's first hard drive, the IBM 350, used a stack of fifty 24-inch platters and was of a size comparable to two large refrigerators. In 1962, IBM introduced its model 1311 disk, which used six 14-inch (nominal size) platters in a removable pack and was roughly the size of a washing machine. This became a standard platter size and drive form-factor for many years, used also by other manufacturers. The IBM 2314 used platters of the


title: "Hard disk drive" content: same size in an eleven-high pack and introduced the "drive in a drawer" layout, although the "drawer" was not the complete drive. Later drives were designed to fit entirely into a chassis that would mount in a 19-inch rack. Digital's RK05 and RL01 were early examples using single 14-inch platters in removable packs, the entire drive fitting in a 10.5-inch-high rack space (six rack units). In the mid-to-late 1980s the similarly sized Fujitsu Eagle, which used (coincidentally) 10.5-inch platters, was a popular product. Such large platters were never used with microprocessor-based systems. With increasing sales of microcomputers having built in


title: "Hard disk drive" content: floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Thus HDD "Form factors", initially followed those of 8-inch, 5.25-inch, and 3.5-inch floppy disk drives. Although referred to by these nominal sizes, the actual sizes for those three drives respectively are 9.5″, 5.75″ and 4″ wide. Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards. 2.5-inch drives are actually 2.75″ wide. , 2.5-inch and 3.5-inch hard disks were the most popular sizes. By 2009, all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch


title: "Hard disk drive" content: and 0.85-inch form factors due to falling prices of flash memory, which has no moving parts. While nominal sizes are in inches, actual dimensions are specified in millimeters. The factors that limit the time to access the data on an HDD are mostly related to the mechanical nature of the rotating disks and moving heads. Seek time is a measure of how long it takes the head assembly to travel to the track of the disk that contains data. The first HDD had an average seek time of about 600 ms. Some early PC drives used a stepper motor to


title: "Hard disk drive" content: move the heads, and as a result had seek times as slow as 80–120 ms, but this was quickly improved by voice coil type actuation in the 1980s, reducing seek times to around 20 ms. Seek time has continued to improve slowly over time. The fastest server drives today have a seek time around 4 ms. The average seek time is strictly the time to do all possible seeks divided by the number of all possible seeks, but in practice is determined by statistical methods or simply approximated as the time of a seek over one-third of the number of


title: "Hard disk drive" content: tracks. Rotational latency is incurred because the desired disk sector may not be directly under the head when data transfer is requested. Average rotational latency is shown in the table, based on the statistical relation that the average latency is one-half the rotational period. The bit rate or data transfer rate (once the head is in the right position) creates delay which is a function of the number of blocks transferred; typically relatively small, but can be quite long with the transfer of large contiguous files. Delay may also occur if the drive disks are stopped to save energy. Defragmentation


title: "Hard disk drive" content: is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk. Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce access delays, performance will be temporarily reduced while the procedure is in progress. Time to access data can be improved by increasing rotational speed (thus reducing latency) or by reducing the time spent seeking. Increasing areal density increases throughput by increasing data rate and by increasing the amount of data under a set of heads, thereby potentially reducing seek activity for a given amount of


title: "Hard disk drive" content: data. The time to access data has not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity. , a typical 7,200-rpm desktop HDD has a sustained "disk-to-buffer" data transfer rate up to 1,030 Mbit/s. This rate depends on the track location; the rate is higher for data on the outer tracks (where there are more data sectors per rotation) and lower toward the inner tracks (where there are fewer data sectors per rotation); and is generally somewhat higher for 10,000-rpm drives. A current widely used standard for the "buffer-to-computer" interface


title: "Hard disk drive" content: is 3.0 Gbit/s SATA, which can send about 300 megabyte/s (10-bit encoding) from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates. Data transfer rate (read/write) can be measured by writing a large file to disk using special file generator tools, then reading back the file. Transfer rate can be influenced by file system fragmentation and the layout of the files. HDD data transfer rate depends upon the rotational speed of the platters and the data recording density. Because heat and vibration limit rotational speed, advancing density becomes the main method to improve


title: "Hard disk drive" content: sequential transfer rates. Higher speeds require a more powerful spindle motor, which creates more heat. While areal density advances by increasing both the number of tracks across the disk and the number of sectors per track, only the latter increases the data transfer rate for a given rpm. Since data transfer rate performance tracks only one of the two components of areal density, its performance improves at a lower rate. Other performance considerations include quality-adjusted price, power consumption, audible noise, and both operating and non-operating shock resistance. The Federal Reserve Board has a quality-adjusted price index for large-scale enterprise storage


title: "Hard disk drive" content: systems including three or more enterprise HDDs and associated controllers, racks and cables. Prices for these large-scale storage systems improved at the rate of ‒30% per year during 2004–2009 and ‒22% per year during 2009–2014. Current hard drives connect to a computer over one of several bus types, including parallel ATA, Serial ATA , SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Some drives, especially external portable drives, use IEEE 1394, or USB. All of these interfaces are digital; electronics on the drive process the analog signals from the read/write heads. Current drives present a consistent interface to the rest


title: "Hard disk drive" content: of the computer, independent of the data encoding scheme used internally, and independent of the physical number of disks and heads within the drive. Typically a DSP in the electronics inside the drive takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction to decode the data, then sends that data out the standard interface. That DSP also watches the error rate detected by error detection and correction, and performs bad sector remapping, data collection for Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks. Modern interfaces connect the drive to the host interface


title: "Hard disk drive" content: with a single data/control cable. Each drive also has an additional power cable, usually direct to the power supply unit. Older interfaces had separate cables for data signals and for drive control signals. Due to the extremely close spacing between the heads and the disk surface, HDDs are vulnerable to being damaged by a head crash – a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by electronic failure, a sudden power failure, physical shock, contamination of the drive's


title: "Hard disk drive" content: internal enclosure, wear and tear, corrosion, or poorly manufactured platters and heads. The HDD's spindle system relies on air density inside the disk enclosure to support the heads at their proper flying height while the disk rotates. HDDs require a certain range of air densities to operate properly. The connection to the external environment and density occurs through a small hole in the enclosure (about 0.5 mm in breadth), usually with a filter on the inside (the "breather filter"). If the air density is too low, then there is not enough lift for the flying head, so the head gets


title: "Hard disk drive" content: too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about . Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disk drives – they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter


title: "Hard disk drive" content: to remove any leftover contaminants from manufacture, any particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity present for extended periods of time can corrode the heads and platters. For giant magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) still results in the head temporarily overheating, due to friction with the disk surface, and can render the data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity", a


title: "Hard disk drive" content: problem which can partially be dealt with by proper electronic filtering of the read signal). When the logic board of a hard disk fails, the drive can often be restored to functioning order and the data recovered by replacing the circuit board with one of an identical hard disk. In the case of read-write head faults, they can be replaced using specialized tools in a dust-free environment. If the disk platters are undamaged, they can be transferred into an identical enclosure and the data can be copied or cloned onto a new drive. In the event of disk-platter failures, disassembly


title: "Hard disk drive" content: and imaging of the disk platters may be required. For logical damage to file systems, a variety of tools, including fsck on UNIX-like systems and CHKDSK on Windows, can be used for data recovery. Recovery from logical damage can require file carving. A common expectation is that hard disk drives designed and marketed for server use will fail less frequently than consumer-grade drives usually used in desktop computers. However, two independent studies by Carnegie Mellon University and Google found that the "grade" of a drive does not relate to the drive's failure rate. A 2011 summary of research, into SSD


title: "Hard disk drive" content: and magnetic disk failure patterns by Tom's Hardware summarized research findings as follows: More than 200 companies have manufactured HDDs over time. But consolidations have concentrated production into just three manufacturers today: Western Digital, Seagate, and Toshiba. Worldwide revenue for disk storage declined 4% per year, from a peak of $38 billion in 2012 to $27 billion in 2016. Production of HDDs grew 16% per year, from 335 exabytes in 2011 to 693 exabytes in 2016. Shipments declined 7% per year during this time period, from 620 million units to 425 million. Seagate and Western Digital each have 40–45% of


title: "Hard disk drive" content: unit shipments, while Toshiba has 13–17%. The average sales price for the two largest manufacturers was $60 per unit in 2015. The maximum areal storage density for flash memory used in solid state drives (SSDs) is 2.8 Tbit/in in laboratory demonstrations as of 2016, and the maximum for HDDs is 1.5 Tbit/in. The areal density of flash memory is doubling every two years, similar to Moore's law (40% per year) and faster than the 10–20% per year for HDDs. As of 2016, maximum capacity was 10 terabytes for an HDD, and 15 terabytes for an SSD. HDDs were used in


title: "Hard disk drive" content: 70% of the desktop and notebook computers produced in 2016, and SSDs were used in 30%. The usage share of HDDs is declining and could drop below 50% in 2018–2019 according to one forecast, because SSDs are replacing smaller-capacity (less than one-terabyte) HDDs in desktop and notebook computers and MP3 players. The market for silicon-based flash memory (NAND) chips, used in SSDs and other applications, is growing rapidly. Worldwide revenue grew 12% per year during 2011–2016. It rose from $22 billion in 2011 to $39 billion in 2016, while production grew 46% per year from 19 exabytes to 120 exabytes.


title: "Hard disk drive" content: External hard disk drives typically connect via USB; variants using USB 2.0 interface generally have slower data transfer rates when compared to internally mounted hard drives connected through SATA. Plug and play drive functionality offers system compatibility and features large storage options and portable design. , available capacities for external hard disk drives ranged from 500 GB to 10 TB. External hard disk drives are usually available as pre-assembled integrated products, but may be also assembled by combining an external enclosure (with USB or other interface) with a separately purchased drive. They are available in 2.5-inch and 3.5-inch sizes; 2.5-inch


title: "Hard disk drive" content: variants are typically called "portable external drives", while 3.5-inch variants are referred to as "desktop external drives". "Portable" drives are packaged in smaller and lighter enclosures than the "desktop" drives; additionally, "portable" drives use power provided by the USB connection, while "desktop" drives require external power bricks. Features such as biometric security or multiple interfaces (for example, Firewire) are available at a higher cost. There are pre-assembled external hard disk drives that, when taken out from their enclosures, cannot be used internally in a laptop or desktop computer due to embedded USB interface on their printed circuit boards, and lack


title: "Hard disk drive" content: of SATA (or Parallel ATA) interfaces. Hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk, is an electromechanical 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


title: "High jump" content: High jump The high jump is a track and field event in which competitors must jump unaided over a horizontal bar placed at measured heights without dislodging it. In its modern most practised format, a bar is placed between two standards with a crash mat for landing. In the modern era, athletes run towards the bar and use the Fosbury Flop method of jumping, leaping head first with their back to the bar. Since ancient times, competitors have introduced increasingly effective techniques to arrive at the current form. The discipline is, alongside the pole vault, one of two vertical clearance


title: "High jump" content: events to feature on the Olympic athletics programme. It is contested at the World Championships in Athletics and IAAF World Indoor Championships, and is a common occurrence at track and field meetings. The high jump was among the first events deemed acceptable for women, having been held at the 1928 Olympic Games. Javier Sotomayor (Cuba) is the current men's record holder with a jump of set in 1993 – the longest standing record in the history of the men's high jump. Stefka Kostadinova (Bulgaria) has held the women's world record at since 1987, also the longest-held record in the event.


title: "High jump" content: The rules for the high jump are set internationally by the International Association of Athletics Federations (IAAF). Jumpers must take off on one foot. A jump is considered a failure if the bar is dislodged by the action of the jumper whilst jumping or the jumper touches the ground or breaks the plane of the near edge of the bar before clearance. The technique one uses for the jump must be almost flawless in order to have a chance of clearing a high bar. Competitors may begin jumping at any height announced by the chief judge, or may pass, at


title: "High jump" content: their own discretion. Most competitions state that three consecutive missed jumps, at any height or combination of heights, will eliminate the jumper from competition. The victory goes to the jumper who clears the greatest height during the final. Tie-breakers are used for any place in which scoring occurs. If two or more jumpers tie for one of these places, the tie-breakers are: 1) the fewest misses at the height at which the tie occurred; and 2) the fewest misses throughout the competition. If the event remains tied for first place (or a limited advancement position to a subsequent meet), the


title: "High jump" content: jumpers have a jump-off, beginning at the next greater height. Each jumper has one attempt. The bar is then alternately lowered and raised until only one jumper succeeds at a given height. The first recorded high jump event took place in Scotland in the 19th century. Early jumpers used either an elaborate straight-on approach or a scissors technique. In latter years, soon then after, the bar was approached diagonally, and the jumper threw first the inside leg and then the other over the bar in a scissoring motion. Around the turn of the 20th century, techniques began to change, beginning


title: "High jump" content: with the Irish-American Michael Sweeney's "Eastern cut-off". By taking off like the scissors and extending his spine and flattening out over the bar, Sweeney raised the world record to in 1895. Another American, George Horine, developed an even more efficient technique, the "Western roll". In this style, the bar again is approached on a diagonal, but the inner leg is used for the take-off, while the outer leg is thrust up to lead the body sideways over the bar. Horine increased the world standard to in 1912. His technique was predominant through the Berlin Olympics of 1936, in which the


title: "High jump" content: event was won by Cornelius Johnson at . American and Soviet jumpers were the most successful for the next four decades, and they pioneered the evolution of the straddle technique. Straddle jumpers took off as in the Western roll, but rotated their (belly-down) torso around the bar, obtaining the most efficient and highest clearance (of the bar) up to that time. Straddle-jumper, Charles Dumas, was the first to clear 7 feet (2.13 m), in 1956, and American John Thomas pushed the world mark to in 1960. Valeriy Brumel took over the event for the next four years. The elegant Soviet


title: "High jump" content: jumper radically sped up his approach run, took the record up to , and won the Olympic gold medal in 1964, before a motorcycle accident ended his career. American coaches, including two-time NCAA champion Frank Costello of the University of Maryland, flocked to Russia to learn from Brumel and his coaches. However, it would be a solitary innovator at Oregon State University, Dick Fosbury, who would bring the high jump into the next century. Taking advantage of the raised, softer landing areas by then in use, Fosbury added a new twist to the outmoded Eastern Cut-off. He directed himself over


title: "High jump" content: the bar head and shoulders first, sliding over on his back and landing in a fashion which would likely have broken his neck in the old, sawdust landing pits. After he used this Fosbury flop to win the 1968 Olympic gold medal, the technique began to spread around the world, and soon "floppers" were dominating international high jump competitions. The last straddler to set a world record was Vladimir Yashchenko, who cleared in 1977 and then indoors in 1978. Among renowned high jumpers following Fosbury's lead were Americans Dwight Stones and his rival, tall Franklin Jacobs of Paterson, NJ, who


title: "High jump" content: cleared , over his head (a feat equalled 27 years later by Sweden's Stefan Holm); Chinese record-setters Ni-chi Chin and Zhu Jianhua; Germans Gerd Wessig and Dietmar Mögenburg; Swedish Olympic medalist and former world record holder Patrik Sjöberg; and female jumpers Iolanda Balaş of Romania, Ulrike Meyfarth of Germany and Italy's Sara Simeoni. The approach run of the high jump may actually be more important than the take-off. If a high jumper runs with bad timing or without enough aggression, clearing a high bar becomes more of a challenge. The approach requires a certain shape or curve, the right amount


title: "High jump" content: of speed, and the correct number of strides. The approach angle is also critical for optimal height. Most great straddle jumpers have a run at angles of about 30 to 40 degrees. The length of the run is determined by the speed of the person's approach. A slower run requires about 8 strides. However, a faster high jumper might need about 13 strides. A greater run speed allows a greater part of the body's forward momentum to be converted upward. The J type approach, favored by Fosbury floppers, allows for horizontal speed, the ability to turn in the air (centripetal


title: "High jump" content: force), and good take-off position. This allows for horizontal momentum to turn into vertical momentum, propelling the jumper off the ground and over the bar. The approach should be a hard controlled stride so that a person does not fall from creating an angle with speed. Athletes should run tall and lean on the curve, from the ankles and not the hips. This allows the correct angle to force their hips to rotate during take-off, which allows their center of gravity to pass under the bar. Unlike the classic straddle technique, where the take-off foot is "planted" in the same


title: "High jump" content: spot at every height, flop-style jumpers must adjust their take-off as the bar is raised. Their approach run must be adjusted slightly so that their take-off spot is slightly further out from the bar in order to allow their hips to clear the bar while still maintaining enough momentum to carry their legs across the bar. Jumpers attempting to reach record heights commonly fail when most of their energy is directed into the vertical effort, and they brush the bar off the standards with the backs of their legs as they stall out in mid-air. An effective approach shape can


title: "High jump" content: be derived from physics. For example, the rate of backward spin required as the jumper crosses the bar to facilitate shoulder clearance on the way up and foot clearance on the way down can be determined by computer simulation. This rotation rate can be back-calculated to determine the required angle of lean away from the bar at plant, based on how long the jumper is on the take-off foot. This information, together with the jumper's speed in the curve, can be used to calculate the radius of the curved part of the approach. This is a lot of work and


title: "High jump" content: requires measurements of running speed and time of take-off foot on the ground. However, one can work in the opposite direction by assuming an approach radius and watching the resulting backward rotation. This only works if some basic rules are followed in how one executes the approach and take-off. Drills can be practiced to solidify the approach. One drill is to run in a straight line (the linear part of the approach) and then run two to three circles spiraling into one another. Another is to run or skip a circle of any size, two to three times in a


title: "High jump" content: row. It is important to train to leap upwards without first leaning into the bar, allowing the momentum of the J approach to carry the body across the bar. In competition the winner is the person who cleared the highest height. In case of a tie, fewer failed attempts at that height are better: "i.e.", the jumper who makes a height on his or her first attempt is placed ahead of someone who clears the same height on the second or third attempt. If there still is a tie, all the failed attempts at lower heights are added up, and


title: "High jump" content: the one with the fewest total misses is declared the winner. If still tied, a playoff is held. Starting height is the next higher height after the overjumped one. If all the competitors clear the height, the bar is raised , and if they fail, the bar is lowered 2 cm. That continues until only one competitor succeeds in overjumping that height, and he or she is declared the winner. In high jump, it helps if the athlete is tall, has long legs, and limited weight on their body. They must have a strong lower body and flexibility helps a


title: "High jump" content: lot as well. High jumpers tend to go through very vigorous training methods to achieve this ideal body frame. High jumpers must have a fast approach so it is crucial to work on speed and also speed endurance. Lots of high jump competitions may take hours and athletes must make sure they have the endurance to last the entire competition. Common sprint endurance workouts for high jumpers include 200-, 400-, and 800-meter training. Other speed endurance training methods such as hill training or a ladder workout may also be used. It is crucial for high jumpers to have strong lower


title: "High jump" content: bodies and cores, as the bar progressively gets higher, the strength of an athlete's legs (along with speed and technique) will help propel them over the bar. Squats, deadlifts, and core exercises will help a high jumper achieve these goals. It is important, however, for a high jumper to keep a slim figure as any unnecessary weight makes it difficult to jump higher. Arguably the most important training for a high jumper is plyometric training. Because high jump is such a technical event, any mistake in the technique could either lead to failure, injury, or both. To prevent these from


title: "High jump" content: happening, high jumpers tend to focus heavily on plyometrics. This includes hurdle jumps, flexibility training, skips, or scissor kick training. Plyometric workouts tend to be performed at the beginning of the workout. Athletes who have won multiple titles at the two most important competitions, the Olympic Games and the World Championships: Kostadinova and Sotomayor are the only high jumpers to have been Olympic Champion, World Champion and broken the world record. All time lists of athletes with the highest recorded jumps above their own height. , 67 different female athletes had ever been able to jump . High jump The


title: "History of modern Greece" content: in September 1939, Greece remained neutral. Despite this declared neutrality, Greece became a target for Mussolini's expansionist policies. Provocations against Greece included the sinking of the Greek cruiser "Elli" on 15 August 1940. Italian troops crossed the border on 28 October 1940, beginning the Greco-Italian War, but were stopped by a determined Greek defence that ultimately drove them back into Albania. Metaxas died suddenly in January 1941. His death raised hopes for a liberalization of his regime and the restoration of parliamentary rule, but King George quashed these hopes when he retained the regime's machinery in place. In the meantime,


title: Horsepower content: motors and other machinery. The definition of the unit varied among geographical regions. Most countries now use the SI unit "watt" for measurement of power. With the implementation of the EU Directive 80/181/EEC on January 1, 2010, the use of horsepower in the EU is permitted only as a supplementary unit. The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in "The Miner's Friend": So that an engine which will raise as much water as two horses, working together at


title: H.263 content: videoconferencing and videotelephony), but it also found use in H.323 (RTP/IP-based videoconferencing), H.320 (ISDN-based videoconferencing), RTSP (streaming media) and SIP (IP-based videoconferencing) solutions. H.263 is a required video coding format in ETSI 3GPP technical specifications for IP Multimedia Subsystem (IMS), Multimedia Messaging Service (MMS) and Transparent end-to-end Packet-switched Streaming Service (PSS). In 3GPP specifications, H.263 video is usually used in 3GP container format. H.263 also found many applications on the internet: much Flash Video content (as used on sites such as YouTube, Google Video, and MySpace) used to be encoded in Sorenson Spark format (an incomplete implementation of H.263). The


title: Histone content: Kornberg showed that a nucleosome on a core promoter prevents the initiation of transcription in vitro, and Michael Grunstein demonstrated that histones repress transcription in vivo, leading to the idea of the nucleosome as a general gene repressor. Relief from repression is believed to involve both histone modification and the action of chromatin-remodeling complexes. Vincent Allfrey and Alfred Mirsky had earlier proposed a role of histone modification in transcriptional activation, regarded as a molecular manifestation of epigenetics. Michael Grunstein and David Allis found support for this proposal, in the importance of histone acetylation for transcription in yeast and the activity


title: Heroin content: of injected heroin and morphine in individuals formerly addicted to opioids; these subjects showed no preference for one drug over the other. Equipotent injected doses had comparable action courses, with no difference in subjects' self-rated feelings of euphoria, ambition, nervousness, relaxation, drowsiness, or sleepiness. The rush is usually accompanied by a warm flushing of the skin, dry mouth, and a heavy feeling in the extremities. Nausea, vomiting, and severe itching may also occur. After the initial effects, users usually will be drowsy for several hours; mental function is clouded; heart function slows; and breathing is also severely slowed, sometimes enough


title: Halloween content: Europe, Japan, and other parts of East Asia. In the Philippines, during Halloween, Filipinos return to their hometowns and purchase candles and flowers, in preparation for the following All Saints Day ("Araw ng mga Patay") on 1 November and All Souls Day – though it falls on 2 November, most of them observe it on the day before. In Mexico and Latin American in general, it is referred to as " Día de los Muertos " which translates in English to "Day of the dead". Most of the people from Latin America construct altars in their homes to honor their


title: Handloading content: reloading, which would be a safety issue. Two sizes of primer pocket uniformer tools exist, the larger one is for large rifle (0.130-inch nominal depth) primer pockets and the smaller one is used for uniforming small rifle/pistol primer pockets. Flash hole uniforming tools are used to remove any burrs, which are residual brass remaining from the manufacturing punching operation used in creating flash holes. These tools resemble primer pocket uniformer tools, except being thinner, and commonly include deburring, chamfering, and uniforming functions. The purpose of these tools is to achieve a more equal distribution of flame from the primer to


title: Habakkuk content: the Great, he went to Ecbatana and remained there until he died, and was buried somewhere nearby, in what is today Tuyserkan. Habakkuk is called both Habaghugh and Hayaghugh by the Muslim locals. The surrounding shrine may date to the period of the Seljuq Empire (11–12th century); it consists of an octagonal wall and conical dome. Underneath the shrine is a hidden basement with three floors. In the center of the shrine's courtyard is the grave where Habakkuk is said to be buried. A stone upon the grave is inscribed in both Hebrew and Persian stating that the prophet's father


title: "Handheld game console" content: July 2005 when Tapwave declared bankruptcy. The Nintendo DS was released in November 2004. Among its new features were the incorporation of two screens, a touchscreen, wireless connectivity, and a microphone port. As with the Game Boy Advance SP, the DS features a clamshell design, with the two screens aligned vertically on either side of the hinge. The DS's lower screen is touch sensitive, designed to be pressed with a stylus, a user's finger or a special "thumb pad" (a small plastic pad attached to the console's wrist strap, which can be affixed to the thumb to simulate an analog


title: "History of mathematics" content: used it in general relativity. Entirely new areas of mathematics such as mathematical logic, topology, and John von Neumann's game theory changed the kinds of questions that could be answered by mathematical methods. All kinds of structures were abstracted using axioms and given names like metric spaces, topological spaces etc. As mathematicians do, the concept of an abstract structure was itself abstracted and led to category theory. Grothendieck and Serre recast algebraic geometry using sheaf theory. Large advances were made in the qualitative study of dynamical systems that Poincaré had begun in the 1890s. Measure theory was developed in the


title: "Hate speech" content: or indirect privileges citizens on the grounds of race, color, political, religious or other beliefs, sex, disability, ethnic or social origin, property status, place of residence, language or other grounds"(Maximum criminal sentence of up to 8 years in prison) Article 300 : "Importation, manufacture or distribution of works promoting a cult of violence and cruelty, racial, national or religious intolerance and discrimination" (Maximum criminal sentence of up to 5 years in prison) In the United Kingdom, several statutes criminalize hate speech against several categories of people. The statutes forbid communication that is hateful, threatening, or abusive, and targets a person


title: "Hoover Dam" content: Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. Originally known as Boulder Dam from 1933, it was officially renamed Hoover Dam, for President Herbert Hoover, by a joint resolution of Congress in 1947. Since about 1900, the Black


title: "Hoover Dam" content: Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc., which began construction on the dam in early 1931. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned the dam over to the federal government on


title: "Hoover Dam" content: March 1, 1936, more than two years ahead of schedule. Hoover Dam impounds Lake Mead, the largest reservoir in the United States by volume (when it is full). The dam is located near Boulder City, Nevada, a municipality originally constructed for workers on the construction project, about southeast of Las Vegas, Nevada. The dam's generators provide power for public and private utilities in Nevada, Arizona, and California. Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year. The heavily traveled U.S. Route 93 (US 93) ran along the dam's crest until October 2010, when


title: "Hoover Dam" content: the Hoover Dam Bypass opened. As the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border; the canal dipped into Mexico before running to a desolate area Beatty named the Imperial Valley. Though water from the Imperial Canal allowed for the widespread settlement of the valley, the canal proved expensive to maintain. After a catastrophic breach that caused the Colorado River to


title: "Hoover Dam" content: fill the Salton Sea, the Southern Pacific Railroad spent $3 million in 1906–07 to stabilize the waterway, an amount it hoped in vain would be reimbursed by the Federal Government. Even after the waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on the Mexican side of the border. As the technology of electric power transmission improved, the Lower Colorado was considered for its hydroelectric-power potential. In 1902, the Edison Electric Company of Los Angeles surveyed the river in the hope of building a rock dam which could generate . However, at the time, the limit of


title: "Hoover Dam" content: transmission of electric power was , and there were few customers (mostly mines) within that limit. Edison allowed land options it held on the river to lapse—including an option for what became the site of Hoover Dam. In the following years, the Bureau of Reclamation (BOR), known as the Reclamation Service at the time, also considered the Lower Colorado as the site for a dam. Service chief Arthur Powell Davis proposed using dynamite to collapse the walls of Boulder Canyon, north of the eventual dam site, into the river. The river would carry off the smaller pieces of debris, and


title: "Hoover Dam" content: a dam would be built incorporating the remaining rubble. In 1922, after considering it for several years, the Reclamation Service finally rejected the proposal, citing doubts about the unproven technique and questions as to whether it would in fact save money. In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado River for flood control and electric power generation. The report was principally authored by Davis, and was called the Fall-Davis report after Interior Secretary Albert Fall. The Fall-Davis report cited use of the Colorado River as a federal concern because the