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Microsoft Connector Bus

Thursday, December 30th, 2010

Microsoft Connector Bus

Thomas and Friends merchandise - GPS Navigator With ISDB-T Player Manufacturer - Mobile Internet Dev

Models

Models of Thomas the Tank Engine and the other characters have been around for as long as The Railway Series of books. Indeed, the Rev. W. Awdry created the original model of Thomas the Tank Engine, which inspired the character, soon after the first book of stories was complete. In 1927, while still at school, he built Annie, and in 1948, he built Clarabel.

The first ever commercially-produced character was Percy the Small Engine, released by Meccano in 1967 as part of a set. However, as this predated the TV Series by at least 20 years, it really counts as 'Railway Series' merchandise.

Several companies have made models of Thomas the Tank Engine and Friends characters, as a result of the TV Series. The Ertl Company, produced an extensive range of die-cast and plastic models; Learning Curve produce the Take Along Thomas and Friends range of travel Thomas playsets; and, more recently, Tomy has introduced a range of die-cast models too.

Press-out card models

The first commercial models released alongside The Railway Series, in 1957, were 'Pre-cut Model Engine Books'. These were full-colour printed cardboard kits whose pieces could be pressed out, folded and glued together to make fairly realistic models. They were produced right through the 1960s. Four titles were published:

"Thomas, with Annie the Coach"

"Percy, with Clarabel the Coach"

"Gordon the Big Engine and his Tender"

"James the Red Engine and his Tender"

The advertisements on the back of the Railway Series books promised, "Other models are being prepared", although, even if ever prepared, they were never published.

Later models

A 12-page "Thomas the Tank Engine Press-out Model Book" (ISBN 0434927589) by the Rev. W. Awdry and Ken Stott, was released in September 1987.

In 1994, a new range of press-out models was released, this time drawn by Ken Stott instead of C. Reginald Dalby. Each book came with accessories, track and a station. The range comprised the following characters: Thomas, Percy, James, Toby, Annie, Clarabel, Bertie the Bus, Harold the Helicopter.

Meccano 'Percy' train set

In 1967, Meccano Ltd released a train set featuring a clockwork model of Percy the Small Engine with some trucks a yellow open wagon and a red closed van and a circle of blue track. The model of Percy was a fair likeness of the pictures in the books and was about the size of an O gauge engine. The box featured special artwork by Peter Edwards and included the title, "Percy the Small Engine, brought to life by Meccano".

The plastic track was advertised as: "Gauge O track that clicks together and includes Brake Rail for automatic braking. Rails specially designed to make it easy to put train on the track." In practice, although it was advertised as 'Gauge O', this only indicated the size of the model, since the track design was not compatible with anything else (the models were effectively 'flangeless').

Adverts for the set, which showed the model train 'emerging' from the book Percy the Small Engine, appeared in Meccano Magazine and on the back of the dust-covers for several of The Railway Series books in print at the time.

The train set was only produced in 1967, and is now extremely rare. It is notable as the last O Gauge train to be made at Meccano's famous Binns Road factory in Liverpool, where the Hornby tinplate trains were made.

Photographs of the set and the adverts may be found here and a close-up of Percy may be found here.

ERTL Models

Ertl was the first company to manufacture numerous models of characters from the Thomas the Tank Engine and Friends TV series. They introduced the first die-cast models in 1985. The range was very popular in the UK, and the nature of the subject matter encouraged collecting. Eventually the range included a large number of models, although it has now been discontinued: Ertl ceased production for the US market in 2001, and for the UK market in 2004.

When the models were first released, they used stickers for faces which could be changed (for some engines, mostly Thomas) to 'happy' or 'sad'. These were soon replaced with fixed plastic faces.

The majority of locomotive models and some road vehicles had a diecast metal body with a moulded plastic chassis and plastic wheels. The bodies were fully painted and lined. They were free-wheeling (rather than motorised) although the chassis was rigid (locomotives were not fitted with separate bogies), and a steam locomotive's tender was part of the same moulding as its body. Models of coaches and trucks were assembled from self-coloured plastic mouldings, with some surface detail (such as coach sides) being applied using self-adhesive labels.

The railway models were designed to be coupled together, so that long trains could be formed. Locomotives had a moulded coupling 'eye' at each end, while rolling stock had one 'hook' and one 'eye'. The unfortunate side-effect of this was that an engine could not 'run-round' to the other end of a train, since, having no hook, there was no means to couple it up. Earlier models had pin couplings, but later ones had moulded loop couplings, with less 'give', and were more prone to breakage.

Unusually for TV Series -related merchandise, the range included a number of characters who only appeared in The Railway Series books, such as those from the Culdee Fell Railway.

The models released are listed on a dedicated page at Train Spotting World.

Miniatures

Around 1991, ERTL started to produce several miniature models of Thomas and his friends. These versions had sticker faces that were previously used in the regular models. They were packaged with random parts of a railway, and once all were collected formed a playset. In later years the models were adapted into keyrings.

The models in this range were essentially the 'major characters' from the TV Series.

The playset components included: a station and siding, a level crossing, a goods yard, engine sheds, a loop track, a windmill, and an airport. Ramp pieces and, later on, viaduct connector pieces were also included.

Ertl 'Gold Rail'

In the 90's ERTL also started another short-lived line called the Gold Rail series. These had no tracks, and the engines and rolling stock had magnetic couplings. The models in this range were about the size of an HO scale train, and were extremely similar to the Bandai range made in Japan. Again the series was comprised from some of the 'major' characters from the TV Series.

Merit products

Another toy company, Merit, produced several sizes of push-along toys to tie-in with the TV series. One such example was a sit-on Thomas built for toddlers, which had a black handle on the rear which enabled it to be pushed along by the parent. Merit also produced large push along toys of Thomas, Annie & Clarabel, Percy and Troublesome Trucks. Another version of the Thomas toy had shaped holes to allow the child to match up the shape with the right hole. All the engines and rolling stock could be coupled up by means of hooks, much like the Ertl models. The company also produced even smaller toys of Thomas, Annie and Clarabel, which could be coupled up in a similar way, except the couplings were on pivots to make it easier for the coaches to follow Thomas when he is pushed along.

Bluebell Toys Miniature Railway

In 1997, Bluebell Toys released an incredibly compact but action-packed playset featuring Thomas, Percy and Bulstrode. The engines and rolling stock had metal rivet wheels that allowed them to run on three-dimensional yellow plastic rails. Features included a tunnel, station and the ability to transfer loads from a truck into Bulstrode. Smaller sets featuring other characters such as James appeared later.

Take Along Thomas & Friends

Take Along Thomas & Friends is a series of die-cast 'Thomas' models made by Learning Curve and designed for preschool children. The models have superseded the Ertl die-cast models range, which has now been discontinued. The two ranges are incompatible as the new models use special 'two-way' magnets instead of the hook-and-loop couplers provided on the Ertl models.

The models are generally much chunkier, and considerably less accurate, than the Ertl range. Many items in the Ertl range were passable as 'scale' models of the TV Series characters, but the Take Along products are much more obviously toys.

The range includes all the major and minor characters from the TV series and Movies, plus Mike, Culdee, and D199 from The Railway Series. The rolling stock models include many of the 'special' (non-speaking) trucks that have featured in single episodes, and the vehicles include the members of The Pack. As well as the individual characters, a number of play-sets have been produced, either containing two or more characters, or a single engine with play scene and DVD. Some specials have been produced with a metallic finish, and a few models are fitted with sound chips and lights.

In 2006, two playsets called Train Yard Set and Working Hard Set were introduced. These were`much bigger than other playsets, being more than 1x1 metres. Original sets were less than 30x30 centimetres.

In 2010, Take-Along was bought by Mattel and became a Fisher-Price line and renamed Take-n-Play. New characters were re-released and the old models were re-released with upgraded paints and faces.

Tomy

Tomy have made several ranges of 'Thomas' models.

Wind-up series

In 1997 Tomy made a range of wind-up models that 'have an action when you wind them up'. The range was small and included only a few of the 'major' characters.

In 2006 another range was introduced. More characters were modelled than previously, and some had moving side rods. Additional models from the range were released in Japan.

Battery-powered

See Thomas Tomica Road & Rail below.

My First Thomas & Friends

My First Thomas & Friends is a range of chunky plastic toys, produced by British toy company: Golden Bear Toys.

The range started in c.1994, and was advertised for young infants who enjoyed the series. The models were safe for younger fans to play with.

The range started with only a dozen or so models, and has now grown to around 40-45, the range was (for a short-lived amount of time) available in America, under the company Tomy. The toys are still available in many good retail toy shops all around the UK, and despite speculation that perhaps the range has discontinued, after the absence of three years without new products; brand new models have started to appear on Amazon.

The range included most of the major and minor characters from the TV Series.

Talking My First Thomas & Friends

The talking versions of the My First Thomas models were first released in 2001. The models are more complex than the basic ones, their eyes move, and they speak familiar phrases from the original stock narrations by Michael Angelis.

Bandai

Other than the Tomix Thomas models Japan has also made a large number of die-cast vehicles. They resembled the "Gold Rail" models made by Ertl. However, this series had more characters, although none from The Railway Series. Most characters from Seasons 1-5 were made. The last new model, to date, is Jack the Frontloader. There have been 4 sets made for this range. Other than this Bandai had made small plastic toys (as big an index finger) labed "Pocket Thomas." There is another series where plastic models (as big as the die-casts) are sold mostly at convenience stores along with candy such as mints and feature more minor characters such as the Mailvan.

Railway systems

Several companies have produced ranges of merchandise where the intention is for the buyer to recreate a complete railway. Such ranges include track, buildings and accessories, in addition to the locomotive and rolling stock character models.

Learning Curve of Chicago produces and distributes the Thomas and Friends Wooden Railway System, which is compatible with BRIO and similar wooden toy trains. Tomy produce a Motor Road and Rail plastic train model set with battery-powered engines and a wide range of track types and Thomas characters.

Learning Curve wooden railway

The Thomas and Friends Wooden Railway (TAFWR) is a wooden railway system created by Learning Curve in Chicago and made in China. This is based on the Thomas the Tank Engine and Friends TV series and The Railway Series and is compatible with the defacto BRIO standard for wooden railway systems.

The majority of characters from the TV Series, both major and minor, plus some of the Railway Series characters, have appeared in the range. They have been accompanied by a comprehensive range of track, buildings and accessories. Also, in 2010 Learning Curve released a small range called Early Engineers, That features the main characters, but have two wheels and are smaller than the normal models.

History, design and construction

The company "Learning Curve" was founded by John W. Lee in Chicago, 1992. In 2003 the company was acquired by "Racing Champions Ertl" that was renamed in the same year to "RC2". Learning Curve introduced some new designs for the track surface of wooden toy railways, such as the "Clicketyclack" rails patented in 1995 and the newer tracks with a relief to supply better traction grip for battery powered trains patented in 2003. They also introduced a road track that uses the same gauge as the railway tracks.

The original models were constructed mainly from painted wood, with metal used in the coupling magnets and axles, and plastic wheels and faces. These models were relatively primitive having simple wooden stubs for the funnel and dome. Details such as windows, whistles and buffer beams were omitted.

In the late 1990s and early 2000s, the models were upgraded. The wooden funnel and painted smokebox were replaced with a separate plastic smokebox with a more realistic-looking funnel. The tender engines received an additional upgrade of moulded plastic 'coal'.

These improved designs were manufactured until 2002 when they were replaced with a third generation of design, which included new and more detailed faces.

Learning Curve continues to expand its lineup of locomotives, rolling stock and locations, although older, less popular, items are 'retired' when appropriate. Every year, begining in 2003, 1-3 retired models are re-released, with upgraded, more realistic shape and paint. These models are only avalible for one year.

Unusual items

Although a number of manufacturers produce ranges of 'Thomas' characters, the TAFWR range is particularly extensive, and includes some models not featured in any other range.

Special model types include "Sights and Sounds" locomotives and buildings, and some battery-powered models. (The majority of locomotives are hand-propelled (push-along).)

Several "Special scene" sets have also been released, modelling significant events in the series, such as "Thomas Comes to Breakfast", with a specially modelled Thomas with a sad face, adorned with a window frame and bush. "James Goes Buzz Buzz", featuring James with a red nose, and one year later "A Better view for Gordon" with flags all over him. These three special edition came each with a thing from the story: The stationmaster's house with Thomas, Knapford with James and the new station came with Gordon. These were brough back in recent months, but they were from newer episodes and are two-car packs. In June 2010, Story Packs will be released, and will contain one or two characters, a destination, a wooden figure, and some track.

The TAFWR includes characters from The Railway Series that have not been televised, such as Ada, Jane, and Mabel (coaches from the Skarloey Railway), Mike and Frank, (from Small Railway Engines), Wilbert (from Wilbert the Forest Engine), D199 (Spamcan), Ivo Hugh, Big City Engine (Foreign Engine), Catherine the Mountain Coach and Culdee (from Mountain Engines). Learning Curve has also made up some of their own models, such as the zoo cars, the Sodor Waterworks cars, the chicken cars and a few more.

Battery-Powered engines were released in the early 2000's are are still avalible. The line originaly included Thomas, Percy, James, Lady, and Bertie (Bertie is discontinued). In 2006, a Salty was released, and in the comimg months a Stanley will be released. A set is avalible that includes Thomas.

In 2009, a range was released called the Talking Railway Series, whitch features several major and minor chacters from the series and when placed on certain destinations they would be addresed by name by Sir Tophamm Hatt a job to do. Egines, destinations, and sets are avalible and the line is still growing. Normal egines can be placed on these destinations, but their name would not be said.

Several of the new characters introduced in Season 11 and Season 13 of the TV series were released by the company some months before the programmes had been broadcast anywhere.

Product recall (June 2007)

On June 13, 2007, the U.S. Consumer Product Safety Commission, with RC2, jointly issued a voluntary product recall notice for a number of the models in the TAFWR range. Tests had discovered lead present in these models, and hence a risk of lead poisoning was recognised. About 1.5 million units are affected, mainly models with red or yellow paint, sold between January 2005 and June 2007. (See recall notice for details of which models are affected.)

Thomas Tomica Road & Rail

Thomas Tomica Road & Rail is a battery-operated system that was introduced by Tomy in March 1992. It was based on the "Plarail" system introduced in Japan in 1959 and made into an electric toy train system in October 1961. As such the toy line is compatible with other Tomy Tomica Road & Rail sets, known as "Plarail system" in Japan and "Tomica World" outside of Japan. The engines run on a plastic blue track, and the roadway vehicles run on a dark gray road. Thomas Tomica Road & Rail is not compatible with most other brands of model railway. It does though have a similar gauge to the wooden toy train systems so that rolling stock may run on both systems to some degree. "Choo Choo Track & Toy Co." for example offers track adapters to connect the wooden tracks with similar gauge such as the blue plastic tracks from Tomy with the dove tail connectors and the tan tracks from Trackmaster. By 2007 the line seems to have been discontinued and theme has been converged to the Trackmaster system.

A large number of models have been released in the range, including the majority of major and minor characters from the TV Series.

This range appears to have changed names several times:

Tomy Trains

Tomica World

Thomas Tomica Road & Rail

Thomas Motor Road & Rail

Tomy has seemed to stopped selling its version of Thomas & Friends in the U.S. market, although it is still available outside of U.S. It has been superseded by the Trackmaster line in the retail stores with the same engines but with a different track system.

Trackmaster Thomas & Friends

In 2007, HIT Entertainment's subsidiary HIT Toys picked up the license to produce the Tomy range formerly known as Thomas Tomica Road & Rail. The Trackmaster engines are compatible with Tomy's Motor Rail and Road merchandise. Trackmaster's light brown coloured track is easily connected to existing blue track from TOMY (two adapters are included in every playset). An innovation in this range is the special face-changing engines that are included in some sets. The rights are now owned by Fisher Price.

Electric railway systems

Electrically-powered model railways have been popular for many years, and several companies have produced ranges of 'Thomas' merchandise to take advantage of this. As for other railway systems, the ranges include track, buildings and accessories, in addition to the locomotive and rolling stock character models. These ranges have the added advantage of being compatible with other, non-'Thomas' models, providing even more variety and play value.

Hornby Railways produce a range of 00 gauge electric 'Thomas' models. The models, based on moulds of real engines, are not finely detailed but are thus suitable for younger enthusiasts. In the United States, Lionel offers a range of Thomas models in the larger O scale. Lionel had previously manufactured Thomas and James models in G scale but dropped this line in 2001. In Japan where space is at a premium and small size is important Tomix have introduced a series of N scale Thomas models.

Hornby Thomas & Friends

Hornby Railways produces a series of 00 gauge model engines, track, accessories and box sets, based on the characters from the TV Series. They are designed to be compatible with other Hornby trains, thus allowing an easy migration to more prototypical modelling.

The models are designed for somewhat older children than most Thomas toys, as placing them correctly on the rails requires a certain degree of dexterity, and the plastic-bodied rolling stock may break if dropped. However, the level of detail is more basic than the 'real' models produced by the company, with the result that the trains can be handled safely by inexperienced hands without fear of damaging delicate parts.

History

Hornby launched its range in its current form in 1985, shortly after the debut of the television series. It mainly utilised modified versions of existing Hornby engines, rolling stock and lineside accessories. Over the following years, the range was expanded to include a large number of the characters from both the TV Series and the Railway Series books.

In addition to the two-rail electric versions, Thomas and Percy were also released as clockwork 'Playtrains'. Percy used the same moulding as his electric counterpart, but Thomas had an entirely unique body which ran on an inaccurate 0-4-0 chassis.

A battery-powered set featuring Thomas, Annie, Clarabel and Bertie the Bus was released, which allowed children to recreate the popular story in which Thomas and Bertie have a race. Thomas was unpowered, being pushed along by a motor in Annie.

Bachmann Thomas & Friends

In 2002 Bachmann USA made their own HO-scale electric Thomas the Tank Engine and Friends range for the US and Canada markets. The models are made with new body tools, to resemble the characters in the TV series. So far over two dozen models have been produced, along with character-themed train sets.

In January 2009, Bachmann announced that, in an agreement with HiT Entertainment, a line of large scale Thomas electric trains will be produced, under the title "Large Scale Thomas & Friends". Bachmann is expected to announce new products for this line at the American International Toy Fair 2009 in New York in February.

Thomas Tomix Rail

From 1998 onwards, a significant range from Tomix has been introduced providing an electric N gauge Thomas system which was still unique in 2007 and which then included 4 locomotives: Thomas, Percy, James and Henry. Some of the rolling stock looked similar to Graham Farish items.

Construction toys

Lego Duplo Thomas & Friends

In 2005, LEGO introduced the first sets in their Duplo 'Thomas' series. Four sets were made, featuring: James the Red Engine, Thomas the Tank Engine, a Troublesome Truck, Toby the Tram Engine, and Percy the Small Engine. Subsequently, in line with usual Lego practice, new sets have been released each year, featuring different scenes and characters.

Duplo is designed for very young children, so the sets have relatively few pieces (between 7 and 62) to assemble.

Thomas character builder

In 2006 MV Sports made their own self-assembly Thomas the Tank Engine and Friends engines and buildings. The range consists of the following models:

Thomas, Toby and Mavis Three Pack Set

Percy Track Set

James and Station Set

Edward and Engine Shed Set

Software

A number of different educational software packages and video games, all based on a 'Thomas' theme, have been released for a variety of different computer platforms.

Commodore

A Commodore 64 game was produced in 1987 whereby Thomas was given a series of seven missions (invariably picking up a coach and taking it to a destination) and a time limit to complete them in. The game featured a fair rendition of the show's distinctive theme tune.

Peakstar

Two PC-based DOS-scrolling games were developed by Peakstar and published by Alternative in 1992 and 1993:

"Thomas the Tank Engine"

"Thomas the Tank Engine 2"

Info about these games can be found at Home of the Underdogs.

Super Nintendo

There was also a game for Super Nintendo which featured a variety of activities such as creating a track for Thomas to get to his destination, races with Percy and Bertie, and three other stories, two of which were based on original stories by the Rev. W. Awdry.

Thomas the Tank Engine & Friends (THQ)

Main article: Thomas the Tank Engine & Friends (video game)

Thomas the Tank Engine & Friends was an educational one-player video game, developed and published by THQ. Released May 1, 1993, it was available for the Super Nintendo and Mega Drive/Genesis platforms. It featured the classic Thomas characters in eight adventures, and included "tricky" trivia questions.

Hasbro Interactive / Infogrames

In 1999, Hasbro Interactive made three Thomas & Friends games based on the television series. After Hasbro was purchased by Infogrames a further three games were released under the Infogrames name.

All of these games were designed as educational games for young children.

Games released by Hasbro

Thomas and Friends: Great Festival Adventures

Thomas and Friends: Trouble on the Tracks

Thomas and Friends: Thomas and the Magic Railroad Print Studio

Games released by Infogrames

Thomas and Friends: Building the New Line

Thomas and Friends: Railway Adventures

Thomas and Friends: Thomas Saves the Day

Microsoft Train Simulator / Trainz

A number of users have created models of the 'Thomas' characters for the train simulator packages made by Microsoft and Auran (Trainz). In these simulators, the user can drive and control a selected engine over a chosen route, created or downloaded by the user.

Many of the characters and items of rolling stock have been created, along with complete routes on the Island of Sodor.

PlayStation 2

A Day at the Races

The first game featuring Thomas for the PlayStation 2. Features: Thomas the Tank Engine, Edward the Blue Engine, James the Red Engine, Percy the Small Engine, The Fat Controller.

Hard Disk Drive

History

Main article: History of hard disk drives

HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally developed for use with general purpose computers. During the 1990s, the need for large-scale, reliable storage, independent of a particular device, led to the introduction of embedded systems such as RAIDs, network attached storage (NAS) systems, and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data. In the 21st century, HDD usage expanded into consumer applications such as camcorders, cellphones (e.g. the Nokia N91), digital audio players, digital video players, digital video recorders, personal digital assistants and video game consoles.

Technology

Diagram of a computer hard disk drive

HDDs record data by magnetizing ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle that holds one or more flat circular disks called platters, onto which the data are recorded. The platters are made from a non-magnetic material, usually aluminum alloy or glass, and are coated with a thin layer of magnetic material, typically 1020 nm in thickness for reference, standard copy paper may be between 0.07 millimetres (70,000 nm) and 0.18 millimetres (180,000 nm) thick. with an outer layer of carbon for protection. Older disks used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy.[citation needed]

A cross section of the magnetic surface in action. In this case the binary data are encoded using frequency modulation.

The platters are spun at very high speeds. Information is written to a platter as it rotates past devices called read-and-write heads that operate very close (tens of nanometers in new drives) over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it. 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.

The magnetic surface of each platter is conceptually divided into many small sub-micrometre-sized magnetic regions, each of which is used to encode a single binary unit of information. Initially the regions were oriented horizontally, but beginning about 2005, the orientation was changed to perpendicular. Due to the polycrystalline nature of the magnetic material each of these magnetic regions is composed of a few hundred magnetic grains. Magnetic grains are typically 10 nm in size and each form a single magnetic domain. Each magnetic region in total forms a magnetic dipole which generates a highly localized magnetic field nearby. A write head magnetizes a region by generating a strong local magnetic field. Early HDDs used an electromagnet both to magnetize the region and to then read its magnetic field by using electromagnetic induction. Later versions of inductive heads included metal in Gap (MIG) heads and thin film heads. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in these heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.

HD heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at, or close to, the platter speed.[citation needed] The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. It's a type of air bearing.

In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other. Another technology used 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.

This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (December 2009)

The grain boundaries turn out to be very important in HDD design. The grains are very small and close to each other, so the coupling between adjacent grains is very strong. When one grain is magnetized, the adjacent grains tend to be aligned parallel to it or demagnetized. Then both the stability of the data and signal-to-noise ratio will be sabotaged. A clear grain boundary can weaken the coupling of the grains and subsequently increase the signal-to-noise ratio. In longitudinal recording, the single-domain grains have uniaxial anisotropy with easy axes lying in the film plane. The consequence of this arrangement is that adjacent magnets repel each other. Therefore the magnetostatic energy is so large that it is difficult to increase areal density. Perpendicular recording media, on the other hand, has the easy axis of the grains oriented perpendicular to the disk plane. Adjacent magnets attract to each other and magnetostatic energy are much lower. So, much higher areal density can be achieved in perpendicular recording. Another unique feature in perpendicular recording is that a soft magnetic underlayer are incorporated into the recording disk. This underlayer is used to conduct writing magnetic flux so that the writing is more efficient. This will be discussed in writing process. Therefore, a higher anisotropy medium film, such as L10-FePt and rare-earth magnets, can be used.

Error handling

Modern drives also make extensive use of Error Correcting Codes (ECCs), particularly Reedolomon error correction. These techniques store extra bits for each block of data that are determined by mathematical formulae. The extra bits allow many errors to be fixed. While these extra bits take up space on the hard drive, they allow higher recording densities to be employed, resulting in much larger storage capacity for user data. In 2009, in the newest drives, low-density parity-check codes (LDPC) are supplanting Reed-Solomon. LDPC codes enable performance close to the Shannon Limit and thus allow for the highest storage density available.

Typical hard drives attempt to "remap" the data in a physical sector that is going bad to a spare physical sectoropefully while the number of errors in that bad sector is still small enough that the ECC can completely recover the data without loss. The S.M.A.R.T. system counts the total number of errors in the entire hard drive fixed by ECC, and the total number of remappings, in an attempt to predict hard drive failure.

See also: file system

Architecture

A hard disk drive with the platters and motor hub removed showing the copper colored stator coils surrounding a bearing at the center of the spindle motor. The orange stripe along the side of the arm is a thin printed-circuit cable. The spindle bearing is in the center.

A typical hard drive has two electric motors, one to spin the disks and one to position the read/write head assembly. The disk motor has an external rotor attached to the platters; the stator windings are fixed in place. The actuator has a read-write head under the tip of its very end (near center); a thin printed-circuit cable connects the read-write head to the hub of the actuator. A flexible, somewhat 'U'-shaped, ribbon cable, seen edge-on below and to the left of the actuator arm in the first image and more clearly in the second, continues the connection from the head to the controller board on the opposite side.

The head support arm is very light, but also rigid; in modern drives, acceleration at the head reaches 550 Gs.

Opened hard drive with top magnet removed, showing copper head actuator coil (top right).

The silver-colored structure at the upper left of the first image is the top plate of the permanent-magnet and moving coil motor that swings the heads to the desired position (it is shown removed in the second image). The plate supports a thin 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 only have one magnet).

The voice coil, itself, is shaped rather like an arrowhead, and made of doubly-coated coppmagnet[clarification needed] wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it's 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) interact with the magnetic field, developing a tangential force that rotates the actuator. Current flowing radially outward along one side of the arrowhead, and radially inward on the other produces the tangential force. (See magnetic field#Force on a charged particle.) 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 N pole, half S pole, with the 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.

Capacity and access speed

PC hard disk drive capacity (in GB) over time. The vertical axis is logarithmic, so the fit line corresponds to exponential growth.

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit them faster.

As of April 2009[update], the highest capacity consumer HDDs are 2 TB.

A typical "desktop HDD" might store between 120 GB and 2 TB although rarely above 500 GB of data (based on US market data), rotate at 5,400 to 15,000 rpm, and have a media transfer rate of 0.5 Gbit/s or higher. (1 GB = 109 Byte; 1 Gbit/s = 109 bit/s)

The fastest nterprise HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s. and a sustained transfer rate up to 1 Gbit/s. Drives running at 10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have less air drag) and therefore generally have lower capacity than the highest capacity desktop drives.

"Mobile HDDs", i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have lower capacity. A typical mobile HDD spins at either 4200rpm, 5400rpm, or 7200rpm, with 5400rpm being the most prominent. 7200rpm drives tend to be more expensive and have smaller capacities, while 4200rpm models usually have very-high storage capacities. Because of physically smaller platter(s), mobile HDDs generally have lower capacity than their larger desktop counterparts.

The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as digital video recorders and digital audio players. In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search, web archiving and video sharing (Google, Internet Archive, YouTube, etc.).

The main way to decrease access time is to increase rotational speed, thus reducing rotational delay, while the main way to increase throughput and storage capacity is to increase areal density. Based on historic trends, analysts predict a future growth in HDD bit density (and therefore capacity) of about 40% per year. Access times have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity.

The expected random IOPS capability of any HDD can be calculated by dividing 1000 msecs by the sum of the average seek time and the average rotational latency.

The first 3.5 HDD marketed as able to store 1 TB was the Hitachi Deskstar 7K1000. It contains five platters at approximately 200 GB each, providing 1 TB (935.5 GiB) of usable space; note the difference between its capacity in decimal units (1 TB = 1012 bytes) and binary units (1 TiB = 1024 GiB = 240 bytes). Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 334 GB platters), Seagate and Western Digital in the 1 TB drive market.

In September 2009, Showa Denko announced capacity improvements in platters that they manufacture for HDD makers. A single 2.5" platter is able to hold 334 GB worth of data, and preliminary results for 3.5" indicate a 750 GB per platter capacity.

Form factor

Width

Largest capacity

Platters (Max)

5.25 FH

146 mm

47 GB (1998)

5.25 HH

146 mm

19.3 GB (1998)

3.5 SATA

102 mm

2 TB (2009)

3.5 PATA

102 mm

750 GB (2006)

2.5 SATA

69.9 mm

1 TB (2009)

2.5 PATA

69.9 mm

320 GB (2009)

1.8 SATA

54 mm

320 GB (2009)

1.8 PATA/LIF

54 mm

240 GB (2008)

1.3

43 mm

40 GB (2007)

1 (CFII/ZIF/IDE-Flex)

42 mm

20 GB (2006)

0.85

24 mm

8 GB (2004)

Capacity measurements

A disassembled and labeled 1997 hard drive. All major components were placed on a mirror, which created the symmetrical reflections.

Raw unformatted capacity of a hard disk drive is usually quoted with SI prefixes (metric system prefixes), incrementing by powers of 1000; today that usually means gigabytes (GB) and terabytes (TB). This is conventional for data speeds and memory sizes which are not inherently manufactured in power of two sizes, as RAM and Flash memory are. Hard disks by contrast have no inherent binary size as capacity is determined by number of heads, tracks and sectors.

This can cause some confusion because some operating systems may report the formatted capacity of a hard drive using binary prefix units which increment by powers of 1024.

A one terabyte (1 TB) disk drive would be expected to hold around 1 trillion bytes (1,000,000,000,000) or 1000 GB; and indeed most 1 TB hard drives will contain slightly more than this number. However some operating system utilities would report this as around 931 GB or 953,674 MB, whereas the correct units would be 931 GiB or 953,674 MiB. (The actual number for a formatted capacity will be somewhat smaller still, depending on the file system). Following are the correct ways of reporting one Terabyte.

SI prefixes (Hard Drive)

equivalent

Binary prefixes (OS)

equivalent

1 TB (Terabytes)

1 * 10004 B

0.9095 TiB (Tebibytes)

0.9095 * 10244 B

1000 GB (Gigabytes)

1000 * 10003 B

931.3 GiB (Gibibytes)

931.3 * 10243 B

1,000,000 MB (Megabytes)

1,000,000 * 10002 B

953,674.3 MiB (Mebibytes)

953,674.3 * 10242 B

1,000,000,000 KB (Kilobytes)

1,000,000,000 * 1000 B

976,562,500 KiB (Kibibytes)

976,562,500 * 1024 B

1,000,000,000,000 B (bytes)

Microsoft Windows reports disk capacity both in a decimal integer to 12 or more digits and in binary prefix units to three significant digits.

The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). Drives with the ATA interface and a capacity of eight gigabytes or more behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with zone bit recording the actual number of sectors varies by zone. Disks with SCSI interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count.

The old C/H/S scheme has been replaced by logical block addressing. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no modern drive has anywhere near 32 platters.

Formatted disk overhead

For a formatted drive, the operating system's file system internal usage is another, although minor, reason why a computer hard drive or storage device's capacity may show its capacity as different from its theoretical capacity. This would include storage for, as examples, a file allocation table (FAT) or inodes, as well as other operating system data structures. This file system overhead is usually less than 1% on drives larger than 100 MB. For RAID drives, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID1 drive will be about half the total capacity as a result of data mirroring. For RAID5 drives with x drives you would lose 1/x of your space to parity. RAID drives are multiple drives that appear to be one drive to the user, but provides some fault-tolerance.

A general rule of thumb to quickly convert the manufacturer's hard disk capacity to the standard Microsoft Windows formatted capacity is 0.93*capacity of HDD from manufacturer for HDDs less than a terabyte and 0.91*capacity of HDD from manufacturer for HDDs equal to or greater than 1 terabyte.

Form factors

5 full height 110 MB HDD,

2 (8.5 mm) 6495 MB HDD,

US/UK pennies for comparison.

Six hard drives with 8, 5.25, 3.5, 2.5, 1.8, and 1 disks, partially disassembled to show platters and read-write heads, with a ruler showing inches.

Before the era of PCs and small computers, hard disks were of widely varying dimensions, typically in free standing cabinets the size of washing machines (e.g. DEC RP06 Disk Drive) or designed so that dimensions enabled placement in a 19" rack (e.g. Diablo Model 31).

With increasing sales of small computers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable, and this led to the evolution of the market towards drives with certain Form factors, initially derived from the sizes of 8", 5.25" and 3.5" floppy disk drives. Smaller sizes than 3.5" have emerged as popular in the marketplace and/or been decided by various industry groups.

8 inch: 9.5 in 4.624 in 14.25 in (241.3 mm 117.5 mm 362 mm)

In 1979, Shugart Associates' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface to the 8 FDD.

5.25 inch: 5.75 in 1.63 in 8 in (146.1 mm 41.4 mm 203 mm)

This smaller form factor, first used in an HDD by Seagate in 1980, was the same size as full height 5-inch diameter FDD, i.e., 3.25 inches high. This is twice as high as "half height" commonly used today; i.e., 1.63 in (41.4 mm). Most desktop models of drives for optical 120 mm disks (DVD, CD) use the half height 5 dimension, but it fell out of fashion for HDDs. The Quantum Bigfoot HDD was the last to use it in the late 1990s, with ow-profile (25 mm) and ltra-low-profile (20 mm) high versions.

3.5 inch: 4 in 1 in 5.75 in (101.6 mm 25.4 mm 146 mm) = 376.77344 cm

This smaller form factor, first used in an HDD by Rodime in 1984, was the same size as the "half height" 3 FDD, i.e., 1.63 inches high. Today it has been largely superseded by 1-inch high limline or ow-profile versions of this form factor which is used by most desktop HDDs.

2.5 inch: 2.75 in 0.3740.59 in 3.945 in (69.85 mm 715 mm 100 mm) = 48.895104.775 cm3

This smaller form factor was introduced by PrairieTek in 1988; there is no corresponding FDD. It is widely used today for hard-disk drives in mobile devices (laptops, music players, etc.) and as of 2008 replacing 3.5 inch enterprise-class drives. It is also used in the Xbox 360 and Playstation 3 video game consoles. Today, the dominant height of this form factor is 9.5 mm for laptop drives, but high capacity drives (750 GB and 1 TB) have a height of 12.5 mm. Enterprise-class drives can have a height up to 15 mm. Seagate has released a wafer-thin 7mm drive aimed at entry level laptops and high end netbooks in December 2009.

1.8 inch: 54 mm 8 mm 71 mm = 30.672 cm

This form factor, originally introduced by Integral Peripherals in 1993, has evolved into the ATA-7 LIF with dimensions as stated. It is increasingly used in digital audio players and subnotebooks. An original variant exists for 25 GB sized HDDs that fit directly into a PC card expansion slot. These became popular for their use in iPods and other HDD based MP3 players.

1 inch: 42.8 mm 5 mm 36.4 mm

This form factor was introduced in 1999 as IBM's Microdrive to fit inside a CF Type II slot. Samsung calls the same form factor "1.3 inch" drive in its product literature.

0.85 inch: 24 mm 5 mm 32 mm

Toshiba announced this form factor in January 2004 for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets. Toshiba currently sells a 4 GB (MK4001MTD) and 8 GB (MK8003MTD) version and holds the Guinness World Record for the smallest hard disk drive.

3.5" and 2.5" hard disks currently dominate the market.

By 2009 all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory.

The inch-based nickname of all these form factors usually do not indicate any actual product dimension (which are specified in millimeters for more recent form factors), but just roughly indicate a size relative to disk diameters, in the interest of historic continuity.

Other characteristics

Data transfer rate

As of 2008, a typical 7200rpm desktop hard drive has a sustained "disk-to-buffer" data transfer rate of about 70 megabytes per second. This rate depends on the track location, so it will be highest for data on the outer tracks (where there are more data sectors) and lower toward the inner tracks (where there are fewer data sectors); and is generally somewhat higher for 10,000rpm drives. A current widely-used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s 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.

Seek time

Seek time currently ranges from just under 2 ms for high-end server drives, to 15 ms for miniature drives, with the most common desktop type typically being around 9 ms.[citation needed] There has not been any significant improvement in this speed for some years. Some early PC drives used a stepper motor to move the heads, and as a result had access times as slow as 80120 ms, but this was quickly improved by voice coil type actuation in the late 1980s, reducing access times to around 20 ms.

Power consumption

Power consumption has become increasingly important, not just in mobile devices such as laptops but also in server and desktop markets. Increasing data center machine density has led to problems delivering sufficient power to devices (especially for spin up), and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see green computing). Similar issues exist for large companies with thousands of desktop PCs. Smaller form factor drives often use less power than larger drives. One interesting development in this area is actively controlling the seek speed so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around (i.e. the rotational latency). Many of the hard drive companies are now producing Green Drives that require much less power and cooling. Many of these 'Green Drives' spin slower (<5400 RPM compared to 7200 RPM, 10,000 RPM, and 15,000 RPM) and also generate less waste heat.

Also in Server and Workstation systems where there might be multiple hard disk drives, there are various ways of controlling when the hard drives spin up (highest power draw).

On SCSI hard disk drives, the SCSI controller can directly control spin up and spin down of the drives.

On Parallel ATA (aka PATA) and SATA hard disk drives, some support Power-up in standby or PUIS. The hard disk drive will not spin up until the controller or system BIOS issues a specific command to do so. This limits the power draw or consumption upon power on.

On newer SATA hard disk drives, there is Staggered Spin Up feature. The hard disk drive will not spin up until the SATA Phy comes ready (communications with the host controller starts).[citation needed]

To further control or reduce power draw and consumption, the hard disk drive can be spun down to reduce its power consumption.

Audible noise

Measured in dBA, audible noise is significant for certain applications, such as PVRs, digital audio recording and quiet computers. Low noise disks typically use fluid bearings, slower rotational speeds (usually 5,400 rpm) and reduce the seek speed under load (AAM) to reduce audible clicks and crunching sounds. Drives in smaller form factors (e.g. 2.5 inch) are often quieter than larger drives .

Shock resistance

Shock resistance is especially important for mobile devices. Some laptops now include active hard drive protection that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event. Maximum shock tolerance to date is 350 Gs for operating and 1000 Gs for non-operating.

Access and interfaces

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Hard disk drives are accessed over one of a number of bus types, including parallel ATA (P-ATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses that they cannot communicate with natively, such as IEEE 1394, USB and SCSI.

For the ST-506 interface, the data encoding scheme as written to the disk surface was also important. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding, and transferred data at a rate of 5 megabits per second. Later controllers using 2,7 RLL (or just "RLL") encoding caused 50% more data to appear under the heads compared to one rotation of an MFM drive, increasing data storage and data transfer rate by 50%, to 7.5 megabits per second.

Many ST-506 interface disk drives were only specified by the manufacturer to run at the 1/3rd lower MFM data transfer rate compared to RLL, while other drive models (usually more expensive versions of the same drive) were specified to run at the higher RLL data transfer rate. In some cases, a drive had sufficient margin to allow the MFM specified model to run at the denser/faster RLL data transfer rate (not recommended nor guaranteed by manufacturers). Also, any RLL-certified drive could run on any MFM controller, but with 1/3 less data capacity and as much as 1/3rd less data transfer rate compared to its RLL specifications.

Enhanced Small Disk Interface (ESDI) also supported multiple data rates (ESDI disks always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives weren't downward compatible (i.e. a 15 or 20 megabit disk drive wouldn't run on a 10 megabit controller). ESDI disk drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size.

Modern hard drives present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a DSP in the electronics inside the hard drive takes the raw analog voltages from the read head and uses PRML and Reedolomon error correction to decode the sector boundaries and sector 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.

SCSI originally had just one signaling frequency of 5 MHz for a maximum data rate of 5 megabytes/second over 8 parallel conductors, but later this was increased dramatically. The SCSI bus speed had no bearing on the disk's internal speed because of buffering between the SCSI bus and the disk drive's internal data bus; however, many early disk drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 disks) when used on slow computers, such as early Commodore Amiga, IBM PC compatibles and Apple Macintoshes.

ATA disks have typically had no problems with interleave or data rate, due to their controller design, but many early models were incompatible with each other and couldn't run with two devices on the same physical cable in a master/slave setup. This was mostly remedied by the mid-1990s, when ATA's specification was standardized and the details began to be cleaned up, but still causes problems occasionally (especially with CD-ROM and DVD-ROM disks, and when mixing Ultra DMA and non-UDMA devices).

Serial ATA does away with master/slave setups entirely, placing each disk on its own channel (with its own set of I/O ports) instead.

FireWire/IEEE 1394 and USB(1.0/2.0) HDDs are external units containing generally ATA or SCSI disks with ports on the back allowing very simple and effective expansion and mobility. Most FireWire/IEEE 1394 models are able to daisy-chain in order to continue adding peripherals without requiring additional ports on the computer itself. USB however, is a point to point network and doesn't allow for daisy-chaining. USB hubs are used to increase the number of available ports and are used for devices that don't require charging since the current supplied by hubs is typically lower than what's available from the built-in USB ports.

Disk interface families used in personal computers

Notable families of disk interfaces include:

Historical bit serial interfaces connect a hard disk drive (HDD) to a hard disk controller (HDC) with two cables, one for control and one for data. (Each drive also has an additional cable for power, usually connecting it directly to the power supply unit). The HDC provided significant functions such as serial/parallel conversion, data separation, and track formatting, and required matching to the drive (after formatting) in order to assure reliability. Each control cable could serve two or more drives, while a dedicated (and smaller) data cable served each drive.

ST506 used MFM (Modified Frequency Modulation) for the data encoding method.

ST412 was available in either MFM or RLL (Run Length Limited) encoding variants.

Enhanced Small Disk Interface (ESDI) was an interface developed by Maxtor to allow faster communication between the processor and the disk than MFM or RLL.

Modern bit serial interfaces connect a hard disk drive to a host bus interface adapter (today typically integrated into the "south bridge") with one data/control cable. (As for historical bit serial interfaces above, each drive also has an additional power cable, usually direct to the power supply unit.)

Fibre Channel (FC), is a successor to parallel SCSI interface on enterprise market. It is a serial protocol. In disk drives usually the Fibre Channel Arbitrated Loop (FC-AL) connection topology is used. FC has much broader usage than mere disk interfaces, and it is the cornerstone of storage area networks (SANs). Recently other protocols for this field, like iSCSI and ATA over Ethernet have been developed as well. Confusingly, drives usually use copper twisted-pair cables for Fibre Channel, not fibre optics. The latter are traditionally reserved for larger devices, such as servers or disk array controllers.

Serial ATA (SATA). The SATA data cable has one data pair for differential transmission of data to the device, and one pair for differential receiving from the device, just like EIA-422. That requires that data be transmitted serially. Similar differential signaling system is used in RS485, LocalTalk, USB, Firewire, and differential SCSI.

Serial Attached SCSI (SAS). The SAS is a new generation serial communication protocol for devices designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses a mechanically identical data and power connector to standard 3.5" SATA1/SATA2 HDDs, and many server-oriented SAS RAID controllers are also capable of addressing SATA hard drives. SAS uses serial communication instead of the parallel method found in traditional SCSI devices but still uses SCSI commands.

Word serial interfaces connect a hard disk drive to a host bus adapter (today typically integrated into the "south bridge") with one cable for combined data/control. (As for all bit serial interfaces above, each drive also has an additional power cable, usually direct to the power supply unit.) The earliest versions of these interfaces typically had a 8 bit parallel data transfer to/from the drive, but 16 bit versions became much more common, and there are 32 bit versions. Modern variants have serial data transfer. The word nature of data transfer makes the design of a host bus adapter significantly simpler than that of the precursor HDD controller.

Integrated Drive Electronics (IDE), later renamed to ATA, with the alias P-ATA ("parallel ATA") retroactively added upon introduction of the new variant Serial ATA. The original name reflected the innovative integration of HDD controller with HDD itself, which was not found in earlier disks. Moving the HDD controller from the interface card to the disk drive helped to standardize interfaces, and to reduce the cost and complexity. The 40 pin IDE/ATA connection transfers 16 bits of data at a time on the data cable. The data cable was originally 40 conductor, but later higher speed requirements for data transfer to and from the hard drive led to an "ultra DMA" mode, known as UDMA. Progressively faster versions of this standard ultimately added the requirement for an 80 conductor variant of the same cable; where half of the conductors provides grounding necessary for enhanced high-speed signal quality by reducing cross talk. The interface for 80 conductor only has 39 pins, the missing pin acting as a key to prevent incorrect insertion of the connector to an incompatible socket, a common cause of disk and controller damage.

EIDE was an unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of direct memory access (DMA) to transfer data between the disk and the computer without the involvement of the CPU, an improvement later adopted by the official ATA standards. By directly transferring data between memory and disk, DMA eliminates the need for the CPU to copy byte per byte, therefore allowing it to process other tasks while the data transfer occurs.

Small Computer System Interface (SCSI), originally named SASI for Shugart Associates System Interface, was an early competitor of ESDI. SCSI disks were standard on servers, workstations, Commodore Amiga and Apple Macintosh computers through the mid-90s, by which time most models had been transitioned to IDE (and later, SATA) family disks. Only in 2005 did the capacity of SCSI disks fall behind IDE disk technology, though the highest-performance disks are still available in SCSI and Fibre Channel only. The length limitations of the data cable allows for external SCSI devices. Originally SCSI data cables used single ended (common mode) data transmission, but server class SCSI could use differential transmission, either low voltage differential (LVD) or high voltage differential (HVD). ("Low" and "High" voltages for differential SCSI are relative to SCSI standards and do not meet the meaning of low voltage and high voltage as used in general electrical engineering contexts, as apply e.g. to statutory electrical codes; both LVD and HVD use low voltage signals (3.3 V and 5 V respectively) in general terminology.)

Acronym or abbreviation

Meaning

Description

SASI

Shugart Associates System Interface

Historical predecessor to SCSI.

SCSI

Small Computer System Interface

Bus oriented that handles concurrent operations.

SAS

Serial Attached SCSI

Improvement of SCSI, uses serial communication instead of parallel.

ST-506

Seagate Technology

Historical Seagate interface.

ST-412

Seagate Technology

Historical Seagate interface (minor improvement over ST-506).

ESDI

Enhanced Small Disk Interface

Historical; backwards compatible with ST-412/506, but faster and more integrated.

ATA

Advanced Technology Attachment

Successor to ST-412/506/ESDI by integrating the disk controller completely onto the device. Incapable of concurrent operations.

SATA

Serial ATA

Modification of ATA, uses serial communication instead of parallel.

Integrity

An IBM HDD head resting on a disk platter. Since the drive is not in operation, the head is simply pressed against the disk by the suspension.

Close-up of a hard disk head resting on a disk platter. A reflection of the head and its suspension is visible on the mirror-like disk.

Due to the extremely close spacing between the heads and the disk surface, any contamination of the read-write heads or platters can lead to 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, wear and tear, corrosion, or poorly manufactured platters and heads.

The HDD's spindle system relies on air pressure inside the enclosure to support the heads at their proper flying height while the disk rotates. Hard disk drives require a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in diameter), usually with a filter on the inside (the breather filter). If the air pressure is too low, then there is not enough lift for the flying head, so the head gets 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 3,000 m (10,000 feet). 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 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 for extended periods 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 problem which can partially be dealt with by proper electronic filtering of the read signal).

Actuation of moving arm

The hard drive'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 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.

Landing zones and load/unload technology

A read/write head from a circa-1998 Fujitsu 3.5" hard disk. The area pictured is approximately 2.0 mm x 3.0mm.

Microphotograph of an older generation hard disk head and slider (1990s). The size of the front face (which is the "trailing face" of the slider) is about 0.3 mm 1.0 mm. It is the location of the actual 'head' (magnetic sensors). The non-visible bottom face of the slider is about 1.0 mm 1.25 mm (so-called "nano" size) and faces the platter. It contains the lithographically micro-machined air bearing surface (ABS) that allows the slider to fly in a highly controlled fashion. One functional part of the head is the round, orange structure visible in the middle - the lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads.

Modern HDDs prevent power interruptions or other malfunctions from landing its heads in the data zone by parking the heads either in a landing zone or by unloading (i.e., load/unload) the heads. Some early PC HDDs did not park the heads automatically and they would land on data. In some other early units the user manually parked the heads by running a program to park the HDD's heads.

A landing zone is an area of the platter usually near its inner diameter (ID), where no data are stored. This area is called the Contact Start/Stop (CSS) zone. Disks are designed such that either a spring or, more recently, rotational inertia in the platters is used to park the heads in the case of unexpected power loss. In this case, the spindle motor temporarily acts as a generator, providing power to the actuator.

Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear. In CSS drives the sliders carrying the head sensors (often also just called heads) are designed to survive a number of landings and takeoffs from the media surface, though wear and tear on these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear: when a disk is younger and has had fewer start-stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage disk (as the head literally drags along the disk's surface until the air bearing is established). For example, the Seagate Barracuda 7200.10 series of desktop hard disks are rated to 50,000 start-stop cycles, in other words no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing.

Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone, thus vastly improving stiction and wear performance. This technology is still largely in use today (2008), predominantly in desktop and enterprise (3.5 inch) drives. In general, CSS technology can be prone to increased stiction (the tendency for the heads to stick to the platter surface), e.g. as a consequence of increased humidity. Excessive stiction can cause physical damage to the platter and slider or spindle motor.

Load/Unload technology relies on the heads being lifted off the platters into a safe location, thus eliminating the risks of wear and stiction altogether. The first HDD RAMAC and most early disk drives used complex mechanisms to load and unload the heads. Modern HDDs use ramp loading, first introduced by Memorex in 1967, to load/unload onto plastic "ramps" near the outer disk edge.

All HDDs today still use one of these two technologies listed above. Each has a list of advantages and drawbacks in terms of loss of storage area on the disk, relative difficulty of mechanical tolerance control, non-operating shock robustness, cost of implementation, etc.

Addressing shock robustness, IBM also created a technology for their ThinkPad line of laptop computers called the Active Protection System. When a sudden, sharp movement is detected by the built-in accelerometer in the Thinkpad, internal hard disk heads automatically unload themselves to reduce the risk of any potential data loss or scratch defects. Apple later also utilized this technology in their PowerBook, iBook, MacBook Pro, and MacBook line, known as the Sudden Motion Sensor. Sony, HP with their HP 3D DriveGuard and Toshiba have released similar technology in their notebook computers.

This accelerometer based shock sensor has also been used for building cheap earthquake sensor networks.

Disk failures and their metrics

Wikibooks has a book on the topic of

Minimizing hard disk drive failure and data loss

Most major hard disk and motherboard vendors now support S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology), which measures drive characteristics such as operating temperature, spin-up time, data error rates, etc. Certain trends and sudden changes in these parameters are thought to be associated with increased likelihood of drive failure and data loss.

However, not all failures are predictable. Normal use eventually can lead to a breakdown in the inherently fragile device, which makes it essential for the user to periodically back up the data onto a separate storage device. Failure to do so will lead to the loss of data. While it may sometimes be possible to recover lost information, it is normally an extremely costly procedure, and it is not possible to guarantee success. A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level; however, the correlation between manufacturer/model and failure rate was relatively strong. Statistics in this matter is kept highly secret by most entities. Google did not publish the manufacturer's names along with their respective failure rates, though they have since revealed that they use Hitachi Deskstar drives in some of their servers. While several S.M.A.R.T. parameters have an impact on failure probability, a large fraction of failed drives do not produce predictive S.M.A.R.T. parameters. S.M.A.R.T. parameters alone may not be useful for predicting individual drive failures.

A common misconception is that a colder hard drive will last longer than a hotter hard drive. The Google study seems to imply the reverse"lower temperatures are associated with higher failure rates". Hard drives with S.M.A.R.T.-reported average temperatures below 27 C (80.6 F) had higher failure rates than hard drives with the highest reported average temperature of 50 C (122 F), failure rates at least twice as high as the optimum S.M.A.R.T.-reported temperature range of 36 C (96.8 F) to 47 C (116.6 F).

SCSI, SAS and FC drives are typically more expensive and are traditionally used in servers and disk arrays, whereas inexpensive ATA and SATA drives evolved in the home computer market and were perceived to be less reliable. This distinction is now becoming blurred.

The mean time between failures (MTBF) of SATA drives is usually about 600,000 hours (some drives such as Western Digital Raptor have rated 1.2 million hours MTBF), while SCSI drives are rated for upwards of 1.5 million hours.[citation needed] However, independent research indicates that MTBF is not a reliable estimate of a drive's longevity. MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disk drive before it enters high volume production. Once the drive product is in production, the more valid metric is annualized failure rate (AFR).[citation needed] AFR is the percentage of real-world drive failures after shipping.

SAS drives are comparable to SCSI drives, with high MTBF and high reliability.[citation needed]

Enterprise S-ATA drives designed and produced for enterprise markets, unlike standard S-ATA drives, have reliability comparable to other enterprise class drives.

Typically enterprise drives (all enterprise drives, including SCSI, SAS, enterprise SATA and FC) experience between 0.70%-0.78% annual failure rates from the total installed drives.[citation needed]

Eventually all mechanical hard disk drives fail. And thus the strategy to mitigate loss of data is to have redundancy in some form, like RAID and backup. RAID should never be relied on as backup, as RAID controllers also break down, making the disks inaccessible. Following a backup strategy; for example, daily differential and weekly full backups, is the only sure way to prevent data loss.

Manufacturers

A Western Digital 3.5 inch 250 GB SATA HDD. This specific model features both SATA and Molex power inputs.

Seagate's hard disk drives being manufactured in a factory in Wuxi, China

See also List of defunct hard disk manufacturers

The technological resources and know-how required for modern drive development and production mean that as of 2010, virtually all of the world's HDDs are manufactured by just five large companies: Seagate, Western Digital, Hitachi, Samsung, and Toshiba.

Dozens of former HDD manufacturers have gone out of business, merged, or closed their HDD divisions; as capacities and demand for products increased, profits became hard to find, and the market underwent significant consolidation in the late 1980s and late 1990s. The first notable casualty of the business in the PC era was Computer Memories Inc. or CMI; after an incident with faulty 20 MB AT disks in 1985, CMI's reputation never recovered, and they exited the HDD business in 1987. Another notable failure was MiniScribe, who went bankrupt in 1990 after it was found that they had engaged in accounting fraud and inflated sales numbers for several years. Many other smaller companies (like Kalok, Microscience, LaPine, Areal, Priam and PrairieTek) also did not survive the shakeout, and had disappeared by 1993; Micropolis was able to hold on until 1997, and JTS, a relative latecomer to the scene, lasted only a few years and was gone by 1999, after attempting to manufacture HDDs in India. Their claim to fame was creating a new 3 form factor drive for use in laptops. Quantum and Integral also invested in the 3 form factor; but eventually ceased support as this form factor failed to catch on. Rodime was also an important manufacturer during the 1980s, but stopped making disks in the early 1990s amid the shakeout and now concentrates on technology licensing; they hold a number of patents related to 3.5-inch form factor HDDs.

The following is the genealogy of the current HDD Companies

1967: Hitachi enters the HDD business.

1967: Toshiba enters the HDD business.

1979: Seagate Technology is founded by a group of ex-IBM and ex-Memorex persons.

1988: Western Digital (WDC), then a well-known controller designer enters the HDD business by acquiring Tandon Corporation's disk manufacturing division.

1989: Seagate Technology purchases Control Data's HDD business.

1990: Maxtor purchases MiniScribe out of bankruptcy, making it the core of its low-end HDDs.

1994: Quantum purchases DEC's storage division, giving it a high-end disk range to go with its more consumer-oriented ProDrive range.

1996: Seagate acquires Conner Peripherals in a merger.

2000: Maxtor acquires Quantum's HDD business; Quantum remains in the tape business.

2003: Hitachi acquires the majority of IBMs disk division, who renamed it Hitachi Global Storage Technologies (HGST).

2006: Seagate acquires Maxtor.

2009: Toshiba acquires Fujitsu's HDD division

Sales

In the year 2007 516.2 million hard disks were sold .

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