Coordinates	20°34′00″N103°40′35″N
name	Automobile
classification	Vehicle
industry	Various
application	Conveyance
fuel source	Gasoline, Diesel, Electric
powered	Yes
self-propelled	Yes
wheels	3–4
axles	0–2
inventor	Ferdinand Verbiest
examples	}}

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the transport of people rather than goods.

The term ''motorcar'' has also been used in the context of electrified rail systems to denote a car which functions as a small locomotive but also provides space for passengers and baggage. These locomotive cars were often used on suburban routes by both interurban and intercity railroad systems.

There are approximately 600 million passenger cars worldwide (roughly one car per eleven people). Around the world, there were about 806 million cars and light trucks on the road in 2007; the engines of these burn over a billion cubic meters (260 billion US gallons) of petrol/gasoline and diesel fuel yearly. The numbers are increasing rapidly, especially in China and India.

Etymology

The word automobile comes, via the French ''automobile'', from the Ancient Greek word αὐτός (''autós'', "self") and the Latin ''mobilis'' ("movable"); meaning a vehicle that moves itself. The alternative name ''car'' is believed to originate from the Latin word ''carrus'' or ''carrum'' ("wheeled vehicle"), or the Middle English word ''carre'' ("cart") (from Old North French), or from the Gaulish word ''karros'' (a Gallic Chariot).

History

The first working steam-powered vehicle was probably designed by Ferdinand Verbiest, a Flemish member of a Jesuit mission in China around 1672. It was a 65 cm-long scale-model toy for the Chinese Emperor, that was unable to carry a driver or a passenger. It is not known if Verbiest's model was ever built.

In 1752, Leonty Shamshurenkov, a Russian peasant, constructed a human-pedalled four-wheeled "auto-running" carriage, and subsequently proposed to equip it with odometer and to use the same principle for making a self-propelling sledge.

Nicolas-Joseph Cugnot is widely credited with building the first self-propelled mechanical vehicle or automobile in about 1769; he created a steam-powered tricycle. He also constructed two steam tractors for the French Army, one of which is preserved in the French National Conservatory of Arts and Crafts. His inventions were however handicapped by problems with water supply and maintaining steam pressure. In 1801, Richard Trevithick built and demonstrated his ''Puffing Devil'' road locomotive, believed by many to be the first demonstration of a steam-powered road vehicle. It was unable to maintain sufficient steam pressure for long periods, and was of little practical use.

In the 1780s, a Russian inventor, Ivan Kulibin, developed a human-pedalled, three-wheeled carriage with an elementary differential transmission of power from the pedals to the axle.

In 1807 Nicéphore Niépce and his brother Claude probably created the world's first internal combustion engine which they called a Pyréolophore, but they chose to install it in a boat on the river Saone in France. Coincidentally, in 1807 the Swiss inventor François Isaac de Rivaz designed his own 'de Rivaz internal combustion engine' and used it to develop the world's first vehicle, to be powered by such an engine. The Niépces' Pyréolophore was fuelled by a mixture of Lycopodium powder (dried Lycopodium moss), finely crushed coal dust and resin that were mixed with oil, whereas de Rivaz used a mixture of hydrogen and oxygen. Neither design was very successful, as was the case with others, such as Samuel Brown, Samuel Morey, and Etienne Lenoir with his hippomobile, who each produced vehicles (usually adapted carriages or carts) powered by clumsy internal combustion engines.

In November 1881, French inventor Gustave Trouvé demonstrated a working three-wheeled automobile powered by electricity at the International Exposition of Electricity, Paris.

Although several other German engineers (including Gottlieb Daimler, Wilhelm Maybach, and Siegfried Marcus) were working on the problem at about the same time, Karl Benz generally is acknowledged as the inventor of the modern automobile.

An automobile powered by his own four-stroke cycle gasoline engine was built in Mannheim, Germany by Karl Benz in 1885, and granted a patent in January of the following year under the auspices of his major company, Benz & Cie., which was founded in 1883. It was an integral design, without the adaptation of other existing components, and included several new technological elements to create a new concept. He began to sell his production vehicles in 1888.

In 1879, Benz was granted a patent for his first engine, which had been designed in 1878. Many of his other inventions made the use of the internal combustion engine feasible for powering a vehicle.

His first ''Motorwagen'' was built in 1885, and he was awarded the patent for its invention as of his application on January 29, 1886. Benz began promotion of the vehicle on July 3, 1886, and about 25 Benz vehicles were sold between 1888 and 1893, when his first four-wheeler was introduced along with a model intended for affordability. They also were powered with four-stroke engines of his own design. Emile Roger of France, already producing Benz engines under license, now added the Benz automobile to his line of products. Because France was more open to the early automobiles, initially more were built and sold in France through Roger than Benz sold in Germany.

In August 1888 Bertha Benz, the wife of Karl Benz, undertook the first road trip by car, to prove the road-worthiness of her husband's invention.

In 1896, Benz designed and patented the first internal-combustion flat engine, called ''boxermotor''. During the last years of the nineteenth century, Benz was the largest automobile company in the world with 572 units produced in 1899 and, because of its size, Benz & Cie., became a joint-stock company.

Daimler and Maybach founded Daimler Motoren Gesellschaft (DMG) in Cannstatt in 1890, and sold their first automobile in 1892 under the brand name, ''Daimler''. It was a horse-drawn stagecoach built by another manufacturer, that they retrofitted with an engine of their design. By 1895 about 30 vehicles had been built by Daimler and Maybach, either at the Daimler works or in the Hotel Hermann, where they set up shop after disputes with their backers. Benz, Maybach and the Daimler team seem to have been unaware of each others' early work. They never worked together; by the time of the merger of the two companies, Daimler and Maybach were no longer part of DMG.

Daimler died in 1900 and later that year, Maybach designed an engine named ''Daimler-Mercedes'', that was placed in a specially ordered model built to specifications set by Emil Jellinek. This was a production of a small number of vehicles for Jellinek to race and market in his country. Two years later, in 1902, a new model DMG automobile was produced and the model was named Mercedes after the Maybach engine which generated 35 hp. Maybach quit DMG shortly thereafter and opened a business of his own. Rights to the ''Daimler'' brand name were sold to other manufacturers.

Karl Benz proposed co-operation between DMG and Benz & Cie. when economic conditions began to deteriorate in Germany following the First World War, but the directors of DMG refused to consider it initially. Negotiations between the two companies resumed several years later when these conditions worsened and, in 1924 they signed an ''Agreement of Mutual Interest'', valid until the year 2000. Both enterprises standardized design, production, purchasing, and sales and they advertised or marketed their automobile models jointly, although keeping their respective brands. On June 28, 1926, Benz & Cie. and DMG finally merged as the ''Daimler-Benz'' company, baptizing all of its automobiles ''Mercedes Benz'', as a brand honoring the most important model of the DMG automobiles, the Maybach design later referred to as the ''1902 Mercedes-35 hp'', along with the Benz name. Karl Benz remained a member of the board of directors of Daimler-Benz until his death in 1929, and at times, his two sons participated in the management of the company as well.

In 1890, Émile Levassor and Armand Peugeot of France began producing vehicles with Daimler engines, and so laid the foundation of the automobile industry in France.

The first design for an American automobile with a gasoline internal combustion engine was made in 1877 by George Selden of Rochester, New York. Selden applied for a patent for an automobile in 1879, but the patent application expired because the vehicle was never built. After a delay of sixteen years and a series of attachments to his application, on November 5, 1895, Selden was granted a United States patent () for a two-stroke automobile engine, which hindered, more than encouraged, development of automobiles in the United States. His patent was challenged by Henry Ford and others, and overturned in 1911.

In 1893, the first running, gasoline-powered American car was built and road-tested by the Duryea brothers of Springfield, Massachusetts. The first public run of the Duryea Motor Wagon took place on September 21, 1893, on Taylor Street in Metro Center Springfield. To construct the Duryea Motor Wagon, the brothers had purchased a used horse-drawn buggy for $70 and then installed a 4 HP, single cylinder gasoline engine. The car had a friction transmission, spray carburetor, and low tension ignition. It was road-tested again on November 10, when the The Springfield Republican newspaper made the announcement. This particular car was put into storage in 1894 and stayed there until 1920 when it was rescued by Inglis M. Uppercu and presented to the United States National Museum.

In Britain, there had been several attempts to build steam cars with varying degrees of success, with Thomas Rickett even attempting a production run in 1860. Santler from Malvern is recognized by the Veteran Car Club of Great Britain as having made the first petrol-powered car in the country in 1894 followed by Frederick William Lanchester in 1895, but these were both one-offs. The first production vehicles in Great Britain came from the Daimler Motor Company, a company founded by Harry J. Lawson in 1896, after purchasing the right to use the name of the engines. Lawson's company made its first automobiles in 1897, and they bore the name ''Daimler''.

In 1892, German engineer Rudolf Diesel was granted a patent for a "New Rational Combustion Engine". In 1897, he built the first Diesel Engine. Steam-, electric-, and gasoline-powered vehicles competed for decades, with gasoline internal combustion engines achieving dominance in the 1910s.

Although various pistonless rotary engine designs have attempted to compete with the conventional piston and crankshaft design, only Mazda's version of the Wankel engine has had more than very limited success.

Mass production

The large-scale, production-line manufacturing of affordable automobiles was debuted by Ransom Olds at his Oldsmobile factory in 1902 based on the assembly line techniques pioneered by Marc Isambard Brunel at the Portsmouth Block Mills, England in 1802. The assembly line style of mass production and interchangeable parts had been pioneered in the U.S. by Thomas Blanchard in 1821, at the Springfield Armory in Springfield, Massachusetts. This concept was greatly expanded by Henry Ford, beginning in 1914.

As a result, Ford's cars came off the line in fifteen minute intervals, much faster than previous methods, increasing productivity eightfold (requiring 12.5 man-hours before, 1 hour 33 minutes after), while using less manpower. It was so successful, paint became a bottleneck. Only Japan black would dry fast enough, forcing the company to drop the variety of colors available before 1914, until fast-drying Duco lacquer was developed in 1926. This is the source of Ford's apocryphal remark, "any color as long as it's black". In 1914, an assembly line worker could buy a Model T with four months' pay.

Ford's complex safety procedures—especially assigning each worker to a specific location instead of allowing them to roam about—dramatically reduced the rate of injury. The combination of high wages and high efficiency is called "Fordism," and was copied by most major industries. The efficiency gains from the assembly line also coincided with the economic rise of the United States. The assembly line forced workers to work at a certain pace with very repetitive motions which led to more output per worker while other countries were using less productive methods.

In the automotive industry, its success was dominating, and quickly spread worldwide seeing the founding of Ford France and Ford Britain in 1911, Ford Denmark 1923, Ford Germany 1925; in 1921, Citroen was the first native European manufacturer to adopt the production method. Soon, companies had to have assembly lines, or risk going broke; by 1930, 250 companies which did not, had disappeared.

Development of automotive technology was rapid, due in part to the hundreds of small manufacturers competing to gain the world's attention. Key developments included electric ignition and the electric self-starter (both by Charles Kettering, for the Cadillac Motor Company in 1910–1911), independent suspension, and four-wheel brakes.

Since the 1920s, nearly all cars have been mass-produced to meet market needs, so marketing plans often have heavily influenced automobile design. It was Alfred P. Sloan who established the idea of different makes of cars produced by one company, so buyers could "move up" as their fortunes improved.

Reflecting the rapid pace of change, makes shared parts with one another so larger production volume resulted in lower costs for each price range. For example, in the 1930s, LaSalles, sold by Cadillac, used cheaper mechanical parts made by Oldsmobile; in the 1950s, Chevrolet shared hood, doors, roof, and windows with Pontiac; by the 1990s, corporate powertrains and shared platforms (with interchangeable brakes, suspension, and other parts) were common. Even so, only major makers could afford high costs, and even companies with decades of production, such as Apperson, Cole, Dorris, Haynes, or Premier, could not manage: of some two hundred American car makers in existence in 1920, only 43 survived in 1930, and with the Great Depression, by 1940, only 17 of those were left.

In Europe much the same would happen. Morris set up its production line at Cowley in 1924, and soon outsold Ford, while beginning in 1923 to follow Ford's practise of vertical integration, buying Hotchkiss (engines), Wrigley (gearboxes), and Osberton (radiators), for instance, as well as competitors, such as Wolseley: in 1925, Morris had 41% of total British car production. Most British small-car assemblers, from Abbey to Xtra had gone under. Citroen did the same in France, coming to cars in 1919; between them and other cheap cars in reply such as Renault's 10CV and Peugeot's 5CV, they produced 550,000 cars in 1925, and Mors, Hurtu, and others could not compete. Germany's first mass-manufactured car, the Opel 4PS ''Laubfrosch'' (Tree Frog), came off the line at Russelsheim in 1924, soon making Opel the top car builder in Germany, with 37.5% of the market.

Weight

The weight of a car influences fuel consumption and performance, with more weight resulting in increased fuel consumption and decreased performance. According to a research conducted by Julian Allwood of the University of Cambridge, global energy use could be heavily reduced by using lighter cars, and an average weight of 500 kg has been said to be well achievable.

In some competitions such as the Shell Eco Marathon, average car weights of 45 kg have also been achieved. These cars are only single-seaters (still falling within the definition of a car, although 4-seater cars are more common), but it nevertheless demonstrates the huge degree in which car weights can still be reduced, and the forthfluing lower fuel use (i.e. up to a fuel use of 2560 km/l.

Fuel and propulsion technologies

Most automobiles in use today are propelled by a internal combustion engine, fueled by deflagration of gasoline (also known as petrol) or diesel. Both fuels are known to cause air pollution and are also blamed for contributing to climate change and global warming. Rapidly increasing oil prices, concerns about oil dependence, tightening environmental laws and restrictions on greenhouse gas emissions are propelling work on alternative power systems for automobiles. Efforts to improve or replace existing technologies include the development of hybrid vehicles, plug-in electric vehicles and hydrogen vehicles. Vehicles using alternative fuels such as ethanol flexible-fuel vehicles and natural gas vehicles are also gaining popularity in some countries.

Safety

While road traffic injuries represent the leading cause in worldwide injury-related deaths, their popularity undermines this statistic.

Mary Ward became one of the first documented automobile fatalities in 1869 in Parsonstown, Ireland and Henry Bliss one of the United States' first pedestrian automobile casualties in 1899 in New York. There are now standard tests for safety in new automobiles, like the EuroNCAP and the US NCAP tests, and insurance industry-backed tests by the Insurance Institute for Highway Safety (IIHS).

Costs and benefits

The costs of automobile usage, which may include the cost of: acquiring the vehicle, repairs, maintenance, fuel, depreciation, injury, driving time, parking fees, tire replacement, taxes, and insurance, are weighed against the cost of the alternatives, and the value of the benefits – perceived and real – of vehicle usage. The benefits may include on-demand transportation, mobility, independence and convenience.

Similarly the costs to society of encompassing automobile use, which may include those of: maintaining roads, land use, pollution, public health, health care, and of disposing of the vehicle at the end of its life, can be balanced against the value of the benefits to society that automobile use generates. The societal benefits may include: economy benefits, such as job and wealth creation, of automobile production and maintenance, transportation provision, society wellbeing derived from leisure and travel opportunities, and revenue generation from the tax opportunities. The ability for humans to move flexibly from place to place has far reaching implications for the nature of societies.

Environmental impact

Transportation is a major contributor to air pollution in most industrialised nations. According to the American Surface Transportation Policy Project nearly half of all Americans are breathing unhealthy air. Their study showed air quality in dozens of metropolitan areas has worsened over the last decade. In the United States the average passenger car emits of the greenhouse gas, carbon dioxide annually, along with smaller amounts of carbon monoxide, hydrocarbons, and nitrogen.

Animals and plants are often negatively impacted by automobiles via habitat destruction and pollution. Over the lifetime of the average automobile the "loss of habitat potential" may be over based on primary production correlations.

Fuel taxes may act as an incentive for the production of more efficient, hence less polluting, car designs (e.g. hybrid vehicles) and the development of alternative fuels. High fuel taxes may provide a strong incentive for consumers to purchase lighter, smaller, more fuel-efficient cars, or to not drive. On average, today's automobiles are about 75 percent recyclable, and using recycled steel helps reduce energy use and pollution. In the United States Congress, federally mandated fuel efficiency standards have been debated regularly, passenger car standards have not risen above the standard set in 1985. Light truck standards have changed more frequently, and were set at in 2007. Alternative fuel vehicles are another option that is less polluting than conventional petroleum powered vehicles.

Other negative effects

Residents of low-density, residential-only sprawling communities are also more likely to die in car collisions which kill 1.2 million people worldwide each year, and injure about forty times this number. Sprawl is more broadly a factor in inactivity and obesity, which in turn can lead to increased risk of a variety of diseases.

Millions of animals are also killed every year on roads by automobiles—so-called Roadkill.

Driverless cars

Fully autonomous vehicles, also known as robotic cars, or driverless cars, already exist in prototype, and are expected to be commercially available around 2020. According to urban designer and futurist Michael E. Arth, driverless electric vehicles—in conjunction with the increased use of virtual reality for work, travel, and pleasure—could reduce the world's 800 million vehicles to a fraction of that number within a few decades. This would be possible if almost all private cars requiring drivers, which are not in use and parked 90% of the time, would be traded for public self-driving taxis that would be in near constant use. This would also allow for getting the appropriate vehicle for the particular need—a bus could come for a group of people, a limousine could come for a special night out, and a Segway could come for a short trip down the street for one person. Children could be chauffeured in supervised safety, DUIs would no longer exist, and 41,000 lives could be saved each year in the US alone.

Future car technologies

Automobile propulsion technology under development include gasoline/electric and plug-in hybrids, battery electric vehicles, hydrogen cars, biofuels, and various alternative fuels.

Research into future alternative forms of power include the development of fuel cells, Homogeneous Charge Compression Ignition (HCCI), stirling engines, and even using the stored energy of compressed air or liquid nitrogen.

New materials which may replace steel car bodies include duraluminum, fiberglass, carbon fiber, and carbon nanotubes.

Telematics technology is allowing more and more people to share cars, on a pay-as-you-go basis, through such schemes as City Car Club in the UK, Mobility in mainland Europe, and Zipcar in the US.

Communication is also evolving due to connected car systems.

Open source development

There have been several projects aiming to develop a car on the principles of open design. The projects include OScar, Riversimple (through 40fires.org) and c,mm,n. None of the projects have reached significant success in terms of developing a car as a whole both from hardware and software perspective and no mass production ready open-source based design have been introduced as of late 2009. Some car hacking through on-board diagnostics (OBD) has been done so far.

Alternatives to the automobile

Established alternatives for some aspects of automobile use include public transit (buses, trolleybuses, trains, subways, monorails, tramways), cycling, walking, rollerblading, skateboarding, horseback riding and using a velomobile. Car-share arrangements and carpooling are also increasingly popular–the US market leader in car-sharing has experienced double-digit growth in revenue and membership growth between 2006 and 2007, offering a service that enables urban residents to "share" a vehicle rather than own a car in already congested neighborhoods. Bike-share systems have been tried in some European cities, including Copenhagen and Amsterdam. Similar programs have been experimented with in a number of US Cities. Additional individual modes of transport, such as personal rapid transit could serve as an alternative to automobiles if they prove to be socially accepted.

Industry

The automotive industry designs, develops, manufactures, markets, and sells the world's motor vehicles. In 2008, more than 70 million motor vehicles, including cars and commercial vehicles were produced worldwide.

In 2007, a total of 71.9 million new automobiles were sold worldwide: 22.9 million in Europe, 21.4 million in Asia-Pacific, 19.4 million in USA and Canada, 4.4 million in Latin America, 2.4 million in the Middle East and 1.4 million in Africa. The markets in North America and Japan were stagnant, while those in South America and other parts of Asia grew strongly. Of the major markets, China, Russia, Brazil and India saw the most rapid growth.

About 250 million vehicles are in use in the United States. Around the world, there were about 806 million cars and light trucks on the road in 2007; they burn over 260 billion gallons of gasoline and diesel fuel yearly. The numbers are increasing rapidly, especially in China and India. In the opinion of some, urban transport systems based around the car have proved unsustainable, consuming excessive energy, affecting the health of populations, and delivering a declining level of service despite increasing investments. Many of these negative impacts fall disproportionately on those social groups who are also least likely to own and drive cars. The sustainable transport movement focuses on solutions to these problems.

In 2008, with rapidly rising oil prices, industries such as the automotive industry, are experiencing a combination of pricing pressures from raw material costs and changes in consumer buying habits. The industry is also facing increasing external competition from the public transport sector, as consumers re-evaluate their private vehicle usage. Roughly half of the US's fifty-one light vehicle plants are projected to permanently close in the coming years, with the loss of another 200,000 jobs in the sector, on top of the 560,000 jobs lost this decade. Combined with robust growth in China, in 2009, this resulted in China becoming the largest automobile producer and market in the world. China 2009 sales had increased to 13.6 million, a significant increase from one million of domestic car sales in 2000.

Market

The automotive market is formed by the demand and the industry. This article is about the general, major trends in the automotive market, mainly from the demand side.

The European automotive market has always boasted a higher number of smaller cars than the United States. With the high fuel prices and the world petroleum crisis, the United States may see its automotive market become more like the European market with fewer large vehicles on the road and more small cars.

For luxurious cars, with the current volatility in oil prices, going for smaller cars is not only smart, but also trendy. And because fashion is of high importance with the upper classes, the little green cars with luxury trimmings become quite plausible.

See also

Air pollution

Bus

Car classification

Carfree city

Driving

List of countries by automobile production

List of countries by vehicles per capita

Lists of automobiles

Motocycle

Motor vehicle theft

Noise pollution

Peak car

Road trip

Steering

Society of Automotive Engineers

Sustainable transport

Traffic collision

Traffic congestion

Truck

U.S. Automobile Production Figures – production figures for each make from 1899 to 2000

References

Further reading

Halberstam, David, ''The Reckoning'', New York, Morrow, 1986. ISBN 0688048382

Kay, Jane Holtz, ''Asphalt nation : how the automobile took over America, and how we can take it back'', New York, Crown, 1997. ISBN 0517587025

Heathcote Williams, ''Autogeddon'', New York, Arcade, 1991. ISBN 1559701765

Wolfgang Sachs: ''For love of the automobile: looking back into the history of our desires'', Berkeley: University of California Press, 1992, ISBN 0520068785

External links

Fédération Internationale de l'Automobile

Forum for the Automobile and Society

Category:Wheeled vehicles

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Coordinates	20°34′00″N103°40′35″N
Name	Parallel ATA
Type	Internal storage device connector
Logo
Designer	Western Digital, subsequently amended by many others
Design date	1986
Superseded by	Serial ATA
Superseded by date	2003
External	No
Hotplug	No
Data bit width	16 bits
Data bandwidth	16 MB/s originally later 33, 66, 100 and 133 MB/s
Data devices	2 (master/slave)
Data style	Parallel
Cable	40 or 80 wires ribbon cable
Num pins	40
Pinout image
Pin1	Reset
Pin2	Ground
Pin3	Data 7
Pin4	Data 8
Pin5	Data 6
Pin6	Data 9
Pin7	Data 5
Pin8	Data 10
Pin9	Data 4
Pin10	Data 11
Pin11	Data 3
Pin12	Data 12
Pin13	Data 2
Pin14	Data 13
Pin15	Data 1
Pin16	Data 14
Pin17	Data 0
Pin18	Data 15
Pin19	Ground
Pin20	Key or VCC_in
Pin21	DDRQ
Pin22	Ground
Pin23	I/O write
Pin24	Ground
Pin25	I/O read
Pin26	Ground
Pin27	IOCHRDY
Pin28	Cable select
Pin29	DDACK
Pin30	Ground
Pin31	IRQ
Pin32	No connect
Pin33	Addr 1
Pin34	GPIO_DMA66_Detect
Pin35	Addr 0
Pin36	Addr 2
Pin37	Chip select 1P
Pin38	Chip select 3P
Pin39	Activity
Pin40	Ground
Pinout notes	}}

Parallel ATA (PATA), originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee. It uses the underlying AT Attachment (ATA) and AT Attachment Packet Interface (ATAPI) standards.

The Parallel ATA standard is the result of a long history of incremental technical development, which began with the original AT Attachment interface, developed for use in early PC AT equipment. The ATA interface itself evolved in several stages from Western Digital's original Integrated Drive Electronics (IDE) interface. As a result, many near-synonyms for ATA/ATAPI and its previous incarnations are still in common informal use. After the introduction of Serial ATA in 2003, the original ATA was retroactively renamed ''Parallel ATA''.

Parallel ATA cables have a maximum allowable length of only . Because of this limit, the technology normally appears as an internal computer storage interface. For many years ATA provided the most common and the least expensive interface for this application. It has largely been replaced by Serial ATA (SATA) in newer systems.

History and terminology

The standard was originally conceived as "PC/AT Attachment" as its primary feature was a direct connection to the 16-bit ISA bus introduced with the IBM PC/AT. The "AT" in "IBM PC/AT" is an initialism for "Advanced Technology," but that term does not appear in current or recent versions of the ATA specification; it is simply "AT Attachment". This name was chosen to avoid possible trademark issues.

IDE and ATA-1

The first version of what is now called the ATA/ATAPI interface was developed by Western Digital under the name ''Integrated Drive Electronics'' (IDE). Together with Control Data Corporation (who manufactured the hard drive part) and Compaq Computer (into whose systems these drives would initially go), they developed the connector, the signaling protocols, and so on with the goal of remaining software compatible with the existing ST-506 hard drive interface. The first such drives appeared in Compaq PCs in 1986.

The term ''Integrated Drive Electronics'' refers not just to the connector and interface definition, but also to the fact that the drive controller is integrated into the drive, as opposed to a separate controller on or connected to the motherboard. The interface cards used to connect a parallel ATA drive to, for example, a PCI slot are not drive controllers, they are merely bridges between the host bus and the ATA interface. Since the original ATA interface is essentially just a 16-bit ISA bus in disguise, the bridge was especially simple in case of an ATA connector being located on an ISA interface card. The integrated controller presented the drive to the host computer as an array of 512-byte blocks with a relatively simple command interface. This relieved the mainboard and interface cards in the host computer of the chores of stepping the disk head arm, moving the head arm in and out, and so on, as had to be done with earlier ST-506 and ESDI hard drives. All of these low-level details of the mechanical operation of the drive were now handled by the controller on the drive itself. This also eliminated the need to design a single controller that could handle many different types of drives, since the controller could be unique for the drive. The host need only ask for a particular sector, or block, to be read or written, and either accept the data from the drive or send the data to it.

The interface used by these drives was standardized in 1994 as ANSI standard X3.221-1994, ''AT Attachment Interface for Disk Drives''. After later versions of the standard were developed, this became known as "ATA-1".

A short-lived, seldom-used implementation of ATA was created for the IBM XT and similar machines that used the 8-bit version of the ISA bus. It has been referred to as "XTA" or "XT Attachment."

Second ATA interface

When PC motherboard makers started to include onboard ATA interfaces in place of the earlier ISA plug-in cards, there was usually only one ATA connector on the board, which could support up to two hard drives. At the time in combination with the floppy drive, this was sufficient for most people, and eventually it became common to have two hard drives installed. When the CD-ROM was developed, many computers would have been unable to accept these drives if they had been ATA devices, due to already having two hard drives installed. Adding the CD-ROM drive would have required removal of one of the drives.

SCSI was available as a CD-ROM expansion option at the time, but devices with SCSI were more expensive than ATA devices due to the need for a smart interface that is capable of bus arbitration. SCSI typically added US$ 100-300 to the cost of a storage device, in addition to the cost of a SCSI host adapter.

The less-expensive solution was the addition of a dedicated CD-ROM interface, typically included as an expansion option on a sound card. It was included on the sound card because early business PCs did not include support for more than simple beeps from the internal speaker, and tuneful sound playback was considered unnecessary for early business software. When the CD-ROM was introduced, it was logical to also add digital audio to the computer at the same time (for the same reason, sound cards tended to include a gameport interface for joysticks). An older business PC could be upgraded in this manner to meet the Multimedia PC standard for early software packages that used sound (which required the sound card) and colorful video animation (which required the CD-ROM as floppy disks simply did not have the necessary data capacity).

The second drive interface initially was not well-defined. It was first introduced with interfaces specific to certain CD-ROM drives such as Mitsumi, Sony or Panasonic drives, and it was common to find early sound cards with two or three separate connectors each designed to match a certain brand of CD-ROM drive. This evolved into the standard ATA interface for ease of cross-compatibility, though the sound card ATA interface still usually supported only a single CD-ROM and not hard drives.

This second ATA interface on the sound card eventually evolved into the second motherboard ATA interface which was long included as a standard component in all PCs. Called the "primary" and "secondary" ATA interfaces, they were assigned to base addresses 0x1F0 and 0x170 on ISA bus systems.

EIDE and ATA-2

In 1994, about the same time that the ATA-1 standard was adopted, Western Digital introduced drives under a newer name, Enhanced IDE (EIDE). These included most of the features of the forthcoming ATA-2 specification and several additional enhancements. Other manufacturers introduced their own variations of ATA-1 such as "Fast ATA" and "Fast ATA-2".

The new version of the ANSI standard, ''AT Attachment Interface with Extensions ATA-2'' (X3.279-1996), was approved in 1996. It included most of the features of the manufacturer-specific variants.

ATA-2 also was the first to note that devices other than hard drives could be attached to the interface:

ATAPI

As mentioned in the previous sections, ATA was originally designed for, and worked only with hard disks and devices that could emulate them. The introduction of ATAPI (ATA Packet Interface) by a group called the Small Form Factor committee (SFF) allowed ATA to be used for a variety of other devices that require functions beyond those necessary for hard disks. For example, any removable media device needs a "media eject" command, and a way for the host to determine whether the media is present, and these were not provided in the ATA protocol.

The Small Form Factor committee approached this problem by defining ATAPI, the "ATA Packet Interface". ATAPI is actually a protocol allowing the ATA interface to carry SCSI commands and responses; therefore all ATAPI devices are actually "speaking SCSI" other than at the electrical interface. In fact, some early ATAPI devices were simply SCSI devices with an ATA/ATAPI to SCSI protocol converter added on. The SCSI commands and responses are embedded in "packets" (hence "ATA Packet Interface") for transmission on the ATA cable. This allows any device class for which a SCSI command set has been defined to be interfaced via ATA/ATAPI.

ATAPI devices are also "speaking ATA", as the ATA physical interface and protocol are still being used to send the packets. On the other hand, ATA hard drives and solid state drives do not use ATAPI.

ATAPI devices include CD-ROM and DVD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive and SuperDisk drive.

The SCSI commands and responses used by each class of ATAPI device (CD-ROM, tape, etc.) are described in other documents or specifications specific to those device classes and are not within ATA/ATAPI or the T13 committee's purview. One commonly used set is defined in the MMC SCSI command set.

ATAPI was adopted as part of ATA in INCITS 317-1998, ''AT Attachment with Packet Interface Extension (ATA/ATAPI-4)''.

UDMA and ATA-4

The ATA/ATAPI-4 also introduced several "Ultra DMA" transfer modes. These initially supported speeds from 16 MByte/s to 33 MByte/second. In later versions faster Ultra DMA modes were added, requiring a new 80-wire cable to reduce crosstalk. The latest versions of Parallel ATA support up to 133 MByte/s.

Current terminology

The terms "integrated drive electronics" (IDE), "enhanced IDE" and "EIDE" have come to be used interchangeably with ATA (now Parallel ATA, or PATA).

In addition there have been several generations of "EIDE" drives marketed, compliant with various versions of the ATA specification. An early "EIDE" drive might be compatible with ATA-2, while a later one with ATA-6.

Nevertheless a request for an "IDE" or "EIDE" drive from a computer parts vendor will almost always yield a drive that will work with most Parallel ATA interfaces.

Another common usage is to refer to the specification version by the fastest mode supported. For example, ATA-4 supported Ultra DMA modes 0 through 2, the latter providing a maximum transfer rate of 33 megabytes per second. ATA-4 drives are thus sometimes called "UDMA-33" drives, and sometimes "ATA-33" drives. Similarly, ATA-6 introduced a maximum transfer speed of 100 megabytes per second, and some drives complying to this version of the standard are marketed as "PATA/100" drives.

x86 BIOS size limitations

Initially the size of an ATA drive was stored in the system x86 BIOS using a type number that predefined the C/H/S parameters. and often the landing zone as well. Which decides where to park the drive heads. Later a "user definable" format called C/H/S or cylinders, heads, sectors were made available. These numbers were important for the earlier ST-506 interface, but were generally meaningless for ATA—the CHS parameters for later ATA large drives often specified impossibly high numbers of heads or sectors that did not actually define the internal physical layout of the drive at all. From the start and up to ATA-2 every user had to specify explicitly how large every attached drive was. From ATA-2 an "identify drive" command were implemented that can be sent and which will return all drive parameters.

Due to a lack of foresight by motherboard manufacturers, the system BIOS was often hobbled by artificial C/H/S size limitations due to the manufacturer assuming certain values would never exceed a certain numerical maximum.

The first of these BIOS limits occurred when ATA drives reached sizes in excess of . Because some motherboard BIOS would not allow C/H/S values above , , and . Multiplied by 512 bytes per sector, this totals which divided by per megabyte, equals 504 megabytes.

The second of these BIOS limitations occurred at 1024 cylinders, 256 heads, and 63 sectors, but a bug in MS-DOS and MS-Windows 95 limit the number heads to 255. This totals to , commonly referred to as the 8.4 gigabyte barrier. This also a limit imposed by x86 BIOSes, and not a limit imposed by the ATA interface.

It was eventually determined that these size limitations could be overridden with a tiny program loaded at startup from a hard drive's boot sector. Some hard drive manufacturers such as Western Digital started including these override utilities with new large hard drives to help overcome these problems. However, if the computer were booted in some other manner without loading the special utility, the invalid BIOS settings would be used, and the drive could either be inaccessible or could appear to be damaged to the operating system.

Later an extension to the x86 BIOS disk services called the "Extended Disk Drive" (EDD) were made available which makes it possible to address drives as large as .

Interface size limitations

Due to lack of foresight the first drive interface used 22-bit addressing mode which resulted in a maximum drive capacity of . Later the first formalized ATA specification used a 28-bit addressing mode, allowing for the addressing of 2²⁸ (blocks) of 512 bytes each, resulting in a maximum capacity of 128 GiB (137 GB).

ATA-6 introduced 48-bit addressing, increasing the limit to 128 PiB (144 PB). As a consequence, any ATA drive of capacity larger than about 137 gigabytes must be an ATA-6 or later drive. Connecting such a drive to a host with an ATA-5 or earlier interface will limit the usable capacity to the maximum of the interface.

Some operating systems, including Windows XP pre-SP 1, and Windows 2000, disable 48-bit LBA by default, requiring the user to take extra steps to use the entire capacity of an ATA drive larger than about 137 gigabytes. Older operating systems, such as Windows 98, do not support 48-bit LBA at all.

Obsolescence

For a long period of time, ATA ruled as the primary storage device interface and in some systems a third and fourth motherboard interface was provided (for example, Promise Ultra-100), for up to eight ATA devices attached to the motherboard.

After the introduction of SATA (Serial ATA), use of Parallel ATA declined, and new motherboards had only a single PATA connector, for up to two PATA optical drives, along with (typically) six or more SATA connectors for hard drives and other devices. In new computers, the parallel ATA interface is rarely used, and several PC chipsets have removed support for PATA, and motherboard vendors still wishing to offer ATA with those chipsets must include an additional interface chip.

Parallel ATA interface

Parallel ATA cables transfer data 16 bits at a time. The traditional cable uses 40-pin connectors attached to a ribbon cable. Each cable has two or three connectors, one of which plugs into an adapter interfacing with the rest of the computer system. The remaining connector(s) plug into drives.

ATA's cables have had 40 wires for most of its history (44 conductors for the smaller form-factor version used for 2.5" drives — the extra four for power), but an 80-wire version appeared with the introduction of the ''Ultra DMA/33'' (''UDMA'') mode. All of the additional wires in the new cable are ground wires, interleaved with the previously defined wires to reduce the effects of capacitive coupling between neighboring signal wires, reducing crosstalk. Capacitive coupling is more of a problem at higher transfer rates, and this change was necessary to enable the 66 megabytes per second (MB/s) transfer rate of ''UDMA4'' to work reliably. The faster ''UDMA5'' and ''UDMA6'' modes also require 80-conductor cables.

Though the number of wires doubled, the number of connector pins and the pinout remain the same as 40-conductor cables, and the external appearance of the connectors is identical. Internally the connectors are different; the connectors for the 80-wire cable connect a larger number of ground wires to a smaller number of ground pins, while the connectors for the 40-wire cable connect ground wires to ground pins one-for-one. 80-wire cables usually come with three differently colored connectors (blue, black, and gray for controller, master drive, and slave drive respectively) as opposed to uniformly colored 40-wire cable's connectors (commonly all gray). The gray connector on 80-conductor cables has pin 28 CSEL not connected, making it the slave position for drives configured cable select.

Round parallel ATA cables (as opposed to ribbon cables) were eventually made available as they were believed to have less effect on computer cooling and were easier to handle; however, only ribbon cables are supported by the ATA specifications.

; Pin 20 In the ATA standard pin 20 is defined as (mechanical) key and is not used. This socket on the female connector is often obstructed, requiring pin 20 to be omitted from the male cable or drive connector, making it impossible to plug it in the wrong way round; a male connector with pin 20 present cannot be used. However, some flash memory drives can use pin 20 as VCC_in to power the drive without requiring a special power cable; this feature can only be used if the equipment supports this use of pin 20.

; Pin 28 Pin 28 of the gray (slave/middle) connector of an 80 conductor cable is not attached to any conductor of the cable. It is attached normally on the black (master drive end) and blue (motherboard end) connectors.

; Pin 34 Pin 34 is connected to ground inside the blue connector of an 80 conductor cable but not attached to any conductor of the cable. It is attached normally on the gray and black connectors. See page 315 of.

Differences between connectors on 80-conductor cables

The image shows PATA connectors after removal of strain relief, cover, and cable. Pin one is at bottom left of the connectors, pin 2 is top left, etc., except that the lower image of the blue connector shows the view from the opposite side, and pin one is at top right.

Each contact comprises a pair of points which together pierce the insulation of the ribbon cable with such precision that they make a connection to the desired conductor without harming the insulation on the neighboring wires. The center row of contacts are all connected to the common ground bus and attached to the odd numbered conductors of the cable. The top row of contacts are the even-numbered sockets of the connector (mating with the even-numbered pins of the receptacle) and attach to every other even-numbered conductor of the cable. The bottom row of contacts are the odd-numbered sockets of the connector (mating with the odd-numbered pins of the receptacle) and attach to the remaining even-numbered conductors of the cable.

Note the connections to the common ground bus from sockets 2 (top left), 19 (center bottom row), 22, 24, 26, 30, and 40 on all connectors. Also note (enlarged detail, bottom, looking from the opposite side of the connector) that socket 34 of the blue connector does not contact any conductor but unlike socket 34 of the other two connectors, it does connect to the common ground bus. On the gray connector, note that socket 28 is completely missing, so that pin 28 of the drive attached to the gray connector will be open. On the black connector, sockets 28 and 34 are completely normal, so that pins 28 and 34 of the drive attached to the black connector will be connected to the cable. Pin 28 of the black drive reaches pin 28 of the host receptacle but not pin 28 of the gray drive, while pin 34 of the black drive reaches pin 34 of the gray drive but not pin 34 of the host. Instead, pin 34 of the host is grounded.

The standard dictates color-coded connectors for easy identification by both installer and cable maker. All three connectors are different from one another. The blue (host) connector has the socket for pin 34 connected to ground inside the connector but not attached to any conductor of the cable. Since the old 40 conductor cables do not ground pin 34, the presence of a ground connection indicates that an 80 conductor cable is installed. The wire for pin 34 is attached normally on the other types and is not grounded. Installing the cable backwards (with the black connector on the system board, the blue connector on the remote device and the gray connector on the center device) will ground pin 34 of the remote device and connect host pin 34 through to pin 34 of the center device. The gray center connector omits the connection to pin 28 but connects pin 34 normally, while the black end connector connects both pins 28 and 34 normally.

Multiple devices on a cable

If two devices attach to a single cable, one must be designated as ''device 0'' (commonly referred to as ''master'') and the other as ''device 1'' (''slave''). This distinction is necessary to allow both drives to share the cable without conflict. The ''master'' drive is the drive that usually appears "first" to the computer's BIOS and/or operating system. On old BIOSes (Intel 486 era and older), the drives are often referred to by the BIOS as "C" for the master and "D" for the slave following the way DOS would refer to the active primary partitions on each.

The mode that a drive must use is often set by a jumper setting on the drive itself, which must be manually set to ''master'' or ''slave''. If there is a single device on a cable, it should be configured as ''master''. However, some hard drives have a special setting called ''single'' for this configuration (Western Digital, in particular). Also, depending on the hardware and software available, a single drive on a cable can work reliably even though configured as the ''slave'' drive (this configuration is most often seen when a CD ROM has a channel to itself).

===Cable select===

A drive mode called ''cable select'' was described as optional in ATA-1 and has come into fairly widespread use with ATA-5 and later. A drive set to "cable select" automatically configures itself as master or slave, according to its position on the cable. Cable select is controlled by pin 28. The host adapter grounds this pin; if a device sees that the pin is grounded, it becomes the master device; if it sees that pin 28 is open, the device becomes the slave device.

This setting is usually chosen by a jumper setting on the drive called "cable select", usually marked ''CS'', which is separate from the "master" or "slave" setting.

Note that if two drives are configured as ''master'' and ''slave'' manually, this configuration does not need to correspond to their position on the cable. Pin 28 is only used to let the drives know their position on the cable; it is not used by the host when communicating with the drives.

With the 40-wire cable it was very common to implement cable select by simply cutting the pin 28 wire between the two device connectors; putting the slave device at the end of the cable, and the master on the middle connector. This arrangement eventually was standardized in later versions. If there is just one device on the cable, this results in an unused stub of cable, which is undesirable for physical convenience and electrical reasons. The stub causes signal reflections, particularly at higher transfer rates.

Starting with the 80-wire cable defined for use in ATAPI5/UDMA4, the master device goes at the end of the cable—the black connector—and the slave device goes on the middle connector—the gray one—and the blue connector goes onto the motherboard. So, if there is only one (master) device on the cable, there is no cable stub to cause reflections. Also, cable select is now implemented in the slave device connector, usually simply by omitting the contact from the connector body.

Master and slave clarification

Although they are in extremely common use, the terms "master" and "slave" do not actually appear in current versions of the ATA specifications. The two devices are simply referred to as "device 0" and "device 1", respectively, in ATA-2 and later.

It is a common myth that the controller on the master drive assumes control over the slave drive, or that the master drive may claim priority of communication over the other device on the channel. In fact, the drivers in the host operating system perform the necessary arbitration and serialization, and each drive's onboard controller operates independently of the other.

The terms "master" and "slave" have not been without controversy. In 2003, the County of Los Angeles, California, US requested that, when possible, suppliers stop using the terms because the county found them unacceptable in light of its "cultural diversity and sensitivity".

Serialized, overlapped, and queued operations

The parallel ATA protocols up through ATA-3 require that once a command has been given on an ATA interface, it must complete before any subsequent command may be given. Operations on the devices must be serialized—with only one operation in progress at a time—with respect to the ATA host interface. A useful mental model is that the host ATA interface is busy with the first request for its entire duration, and therefore can not be told about another request until the first one is complete. The function of serializing requests to the interface is usually performed by a device driver in the host operating system.

The ATA-4 and subsequent versions of the specification have included an "overlapped feature set" and a "queued feature set" as optional features, both being given the name "Tagged Command Queuing", a reference to a set of features from SCSI which the ATA version attempts to emulate. However, support for these is extremely rare in actual parallel ATA products and device drivers because these feature sets were implemented in such a way as to maintain software compatibility with its heritage as originally an extension of the ISA bus. This implementation resulted in excessive CPU utilization which largely negated the advantages of command queuing. By contrast, overlapped and queued operations have been common in other storage buses, in particular, SCSI's version of tagged command queuing had no need to be software compatible with ISA's APIs, allowing it to attain high performance with low overhead on buses which supported first party DMA like PCI. This has long been seen as a major advantage of SCSI.

The Serial ATA standard has supported native command queueing since its first release, but it is an optional feature for both host-adapters and target-devices. Many less expensive PC motherboards do not support NCQ. Many SATA/II hard drives sold today support NCQ, while no removable (CD/DVD) drives do because the ATAPI command set used to control them prohibits queued operations.

Two devices on one cable — speed impact

There are many debates about how much a slow device can impact the performance of a faster device on the same cable. There is an effect, but the debate is confused by the blurring of two quite different causes, called here "Lowest speed" and "One operation at a time".

"Lowest speed"

It is a common misconception that, if two devices of different speed capabilities are on the same cable, both devices' data transfers will be constrained to the speed of the slower device.

For all modern ATA host adapters this is not true, as modern ATA host adapters support ''independent device timing''. This allows each device on the cable to transfer data at its own best speed. Even with older adapters without independent timing, this effect only applies to the data transfer phase of a read or write operation. This is usually the shortest part of a complete read or write operation.

"One operation at a time"

This is caused by the omission of both overlapped and queued feature sets from most parallel ATA products. Only one device on a cable can perform a read or write operation at one time, therefore a fast device on the same cable as a slow device under heavy use will find it has to wait for the slow device to complete its task first.

However, most modern devices will report write operations as complete once the data is stored in its onboard cache memory, before the data is written to the (slow) magnetic storage. This allows commands to be sent to the other device on the cable, reducing the impact of the "one operation at a time" limit.

The impact of this on a system's performance depends on the application. For example, when copying data from an optical drive to a hard drive (such as during software installation), this effect probably doesn't matter: Such jobs are necessarily limited by the speed of the optical drive no matter where it is. But if the hard drive in question is also expected to provide good throughput for other tasks at the same time, it probably should not be on the same cable as the optical drive.

HDD passwords and security

The disk lock is a built-in security feature in the disk. It is part of the ATA specification, and thus not specific to any brand or device. The disk lock can be enabled and disabled by sending special ATA commands to the drive. If a disk is locked, it will refuse all access until it is unlocked.

A disk always has two passwords: A User password and a Master password. Most disks support a Master Password Revision Code. Reportedly some disks can report if the Master password has been changed, or if it still the factory default. The revision code is word 92 in the IDENTIFY response. Reportedly on some disks a value of 0xFFFE means the Master password is unchanged. The standard does not distinguish this value.

A disk can be locked in two modes: High security mode or Maximum security mode. Bit 8 in word 128 of the IDENTIFY response shows which mode the disk is in: 0 = High, 1 = Maximum.

In High security mode, the disk can be unlocked with either the User or Master password, using the "SECURITY UNLOCK DEVICE" ATA command. There is an attempt limit, normally set to 5, after which the disk must be power cycled or hard-reset before unlocking can be attempted again. Also in High security mode the SECURITY ERASE UNIT command can be used with either the User or Master password.

In Maximum security mode, the disk cannot be unlocked without the User password — the only way to get the disk back to a usable state is to issue the SECURITY ERASE PREPARE command, immediately followed by SECURITY ERASE UNIT. In Maximum security mode the SECURITY ERASE UNIT command requires the Master password and will completely erase all data on the disk. The operation is slow, it may take longer than half an hour or more, depending on the size of the disk. (Word 89 in the IDENTIFY response indicates how long the operation will take.)

While the ATA disk lock is intended to be impossible to defeat without a valid password, there are workarounds to unlock a drive. Many data recovery companies offer unlocking services, so while the disk lock will deter a casual attacker, it is not secure against a qualified adversary.

External parallel ATA devices

It is extremely uncommon to find external PATA devices that directly use the interface for connection to a computer. PATA is primarily restricted to devices installed internally, due to the short data cable specification. A device connected externally needs additional cable length to form a U-shaped bend so that the external device may be placed alongside, or on top of the computer case, and the standard cable length is too short to permit this.

For ease of reach from motherboard to device, the connectors tend to be positioned towards the front edge of motherboards, for connection to devices protruding from the front of the computer case. This front-edge position makes extension out the back to an external device even more difficult. Ribbon cables are poorly shielded, and the standard relies upon the cabling to be installed inside a shielded computer case to meet RF emissions limits.

All external PATA devices, such as external hard drives, use some other interface technology to bridge the distance between the external device and the computer. USB is the most common external interface, followed by Firewire. A bridge chip inside the external devices converts from the USB interface to PATA, and typically only supports a single external device without cable select or master/slave.

Compact Flash interface

Compact flash is essentially just a miniaturized ATA interface, for use on devices that use flash memory storage. No interfacing chips or circuitry are required, other than to directly adapt the smaller CF socket onto the larger ATA connector.

The ATA connector specification does not include pins for supplying power to a CF device, so power is inserted into the connector from a separate source.

CF devices can be designated as master or slave on an ATA interface, though since most CF devices offer only a single socket, it is not necessary to offer this selection to end users.

Although CF can be hot pluggable with additional design methods, by default when wired directly to an ATA interface, it is not intended to be hot-pluggable.

ATA standards versions, transfer rates, and features

The following table shows the names of the versions of the ATA standards and the transfer modes and rates supported by each. Note that the transfer rate for each mode (for example, 66.7 MB/s for UDMA4, commonly called "Ultra-DMA 66", defined by ATA-5) gives its maximum theoretical transfer rate on the cable. This is simply two bytes multiplied by the effective clock rate, and presumes that every clock cycle is used to transfer end-user data. In practice, of course, protocol overhead reduces this value.

Congestion on the host bus to which the ATA adapter is attached may also limit the maximum burst transfer rate. For example, the maximum data transfer rate for conventional PCI bus is 133 MB/s, and this is shared among all active devices on the bus.

In addition, no ATA hard drives existed in 2005 that were capable of measured sustained transfer rates of above 80 MB/s. Furthermore, sustained transfer rate tests do not give realistic throughput expectations for most workloads: They use I/O loads specifically designed to encounter almost no delays from seek time or rotational latency. Hard drive performance under most workloads is limited first and second by those two factors; the transfer rate on the bus is a distant third in importance. Therefore, transfer speed limits above 66 MB/s really affect performance only when the hard drive can satisfy all I/O requests by reading from its internal cache — a very unusual situation, especially considering that such data are usually already buffered by the operating system.

As of April 2010 mechanical hard disk drives can transfer data at up to 157 MB/s, which is beyond the capabilities of the PATA/133 specification. High-performance flash drives can transfer data at up to 308 MB/s.

Only the Ultra DMA modes use CRC to detect errors in data transfer between the controller and drive. This is a 16 bit CRC, and it is used for data blocks only. Transmission of command and status blocks do not use the fast signaling methods that would necessitate CRC. For comparison, in Serial ATA, 32 bit CRC is used for both commands and data.

Features introduced with each ATA revision

Programmed input/output ATA, IDE 128 Gibibyte EIDE, , , EIDE ATA-4, ATA-5, ATA-6, 128 Pebibyte ATA-7, ATA-8

Standard	! Other Names	! New Transfer Modes	! Maximum disk size(512 byte sector)	! Other New Features	! ANSI Reference
IDE (pre-ATA)	IDE	PIO 0 || 2 GiB (2.1 GB) ||	22-bit logical block addressing (LBA)	-
ATA-1	|	Multi-word DMA 0	GiB (137 GB) ||	28-bit logical block addressing (LBA)	X3.221-1994(obsolete since 1999)
ATA-2	|	WDMA (computer)>Multi-word DMA 1, 2		PCMCIA connector. Identify drive command.	X3.279-1996(obsolete since 2001)
ATA-3	|	WDMA (computer)>Single-word DMA modes dropped		S.M.A.R.T., Security, 44 pin connector for 2.5" drives	X3.298-1997(obsolete since 2002)
ATA/ATAPI-4	|	aka UDMA/33		AT Attachment Packet Interface (ATAPI) (support for CD-ROM, tape drives etc.), Optional overlapped and queued command set features, Host Protected Area (HPA), CompactFlash Association (CFA) feature set for solid state drives	NCITS 317-1998
ATA/ATAPI-5	|	Ultra DMA 3, 4aka UDMA/66		80-wire cables; CompactFlash connector	NCITS 340-2000
ATA/ATAPI-6	|	UDMA 5aka UDMA/100	PiB (144 PB) ||	48-bit LBA, Device Configuration Overlay (DCO),Automatic Acoustic Management (AAM)	NCITS 361-2002
ATA/ATAPI-7	|	UDMA 6aka UDMA/133SATA/150		Serial ATA>SATA 1.0, Streaming feature set, long logical/physical sector feature set for non-packet devices	NCITS 397-2005 (vol 1)NCITS 397-2005 (vol 2)NCITS 397-2005 (vol 3)
ATA/ATAPI-8	|	—		Hybrid drive featuring non-volatile cache to speed up critical OS files	In progress

Speed of defined transfer modes

+Transfer Modes	Mode	#	Maximum transfer rate<	(MB/s)
rowspan=5>Programmed input/output	PIO	0	3.3
1	5.2
2	8.3
3	11.1
4	16.7
rowspan=3	Single-word DMA	0	2.1
1	4.2
2	8.3
rowspan=5	Multi-word DMA	0	4.2
1	13.3
2	16.7
3<		20
4	25
rowspan=8>Ultra DMA	0	16.7
1	25.0
2 (Ultra ATA/33)	33.3
3	44.4
4 (Ultra ATA/66)	66.7
5 (Ultra ATA/100)	100
6 (Ultra ATA/133)	133
7 (Ultra ATA/167)	167

Related standards, features, and proposals

ATAPI Removable Media Device (ARMD)

ATAPI devices with removable media, other than CD and DVD drives, are classified as ARMD (ATAPI Removable Media Device) and can appear as either a super-floppy (non-partitioned media) or a hard drive (partitioned media) to the operating system. These can be supported as bootable devices by a BIOS complying with the ATAPI Removable Media Device BIOS Specification, originally developed by Compaq Computer Corporation and Phoenix Technologies. It specifies provisions in the BIOS of a personal computer to allow the computer to be bootstrapped from devices such as Zip drives, Jaz drives, SuperDisk (LS-120) drives, and similar devices.

These devices have removable media like floppy disk drives, but capacities more commensurate with hard drives, and programming requirements unlike either. Due to limitations in the floppy controller interface most of these devices were ATAPI devices, connected to one of the host computer's ATA interfaces, similarly to a hard drive or CD-ROM device. However, existing BIOS standards did not support these devices. An ARMD-compliant BIOS allows these devices to be booted from and used under the operating system without requiring device-specific code in the OS.

A BIOS implementing ARMD allows the user to include ARMD devices in the boot search order. Usually an ARMD device is configured earlier in the boot order than the hard drive. Similarly to a floppy drive, if bootable media is present in the ARMD drive, the BIOS will boot from it; if not, the BIOS will continue in the search order, usually with the hard drive last.

There are two variants of ARMD, ARMD-FDD and ARMD-HDD. Originally ARMD caused the devices to appear as a sort of very large floppy drive, either the primary floppy drive device 00h or the secondary device 01h. Some operating systems required code changes to support floppy disks with capacities far larger than any standard floppy disk drive. Also, standard-floppy disk drive emulation proved to be unsuitable for certain high-capacity floppy disk drives such as Iomega Zip drives. Later the ARMD-HDD, ARMD-"Hard disk device", variant was developed to address these issues. Under ARMD-HDD, an ARMD device appears to the BIOS and the operating system as a hard drive.

ATA over Ethernet

In August 2004, Sam Hopkins and Brantley Coile of Coraid specified a lightweight ATA over Ethernet protocol to carry ATA commands over Ethernet instead of directly connecting them to a PATA host adapter. This permitted the established block protocol to be reused in storage area network (SAN) applications.

See also

Master/slave (technology)

Advanced Host Controller Interface (AHCI)

List of device bandwidths

CE-ATA Consumer Electronics (CE) ATA

Serial ATA

FATA (hard drive)

SCSI

BIOS for BIOS Boot Specification (BBS)

INT 13H for BIOS Enhanced Disk Drive Specification (SFF-8039i)

ATA over Ethernet (AoE)

References

Category:Advanced Technology Attachment Category:Computer storage buses

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