title: Siege of Orléans

text: The agreement would have given the English the chance to pass through Orléans and strike into Bourges, the administrative capital of the Dauphin, which had been the primary motivator for the siege itself. Burgundy hurried to Paris in early April to persuade the English regent John of Bedford to take the offer. But Bedford, certain Orléans was on the verge of falling, refused to surrender his prize. The disappointed Philip withdrew his Burgundian auxiliaries from the English siege in a huff. The Burgundian contingent left on 17 April 1429, which left the English with an extremely small army to prosecute the siege. The decision proved to be a lost opportunity, and a terrible mistake in the long run for the English.


title: Siege of Orléans

text: It was on the very day of the Battle of the Herrings that a young French peasant girl, Joan of Arc, was meeting with Robert de Baudricourt, the "Dauphinois" captain of Vaucouleurs, trying to explain to the skeptical captain her divinely-ordained mission to rescue the Dauphin Charles and deliver him to his royal coronation at Reims. She had met and been rebuffed by Baudricourt twice before, but apparently this time he assented and arranged to escort her to the Dauphin's court in Chinon. According to the "Chronique de la Pucelle", at this meeting with Baudricourt, Joan disclosed that the Dauphin's arms had suffered a great reversal near Orléans that day, and if she were not sent to him soon, there would be others. Accordingly, when news of the defeat at Rouvray reached Vaucouleurs, Baudricourt became convinced of the girl's prescience and agreed to escort her. Whatever the truth of the story – and it is not accepted by all authorities – Joan left Vaucouleurs on 23 February for Chinon.


title: Siege of Orléans

text: For years, vague prophecies had been circulating in France concerning an armored maiden who would rescue France. Many of these prophecies foretold that the armored maiden would come from the borders of Lorraine, where Domrémy, Joan's birthplace, is located. As a result, when word reached the besieged citizens of Orléans concerning Joan's journey to see the King, expectations and hopes were high.


title: Siege of Orléans

text: Escorted by several of Baudricourt's soldiers, Joan arrived in Chinon on 6 March 1429 and met with the skeptical La Trémoille. On 9 March she finally met the Dauphin Charles, although it would be a few days more before she had a private meeting where the Dauphin was finally convinced of her "powers" (or at least, her usefulness). Nonetheless, he insisted she first proceed to Poitiers to be examined by church authorities. With the clerical verdict that she posed no harm and could be safely taken on, Dauphin Charles finally accepted her services on 22 March. She was provided with a suit of plate armor, a banner, a pageboy, and heralds.


title: Siege of Orléans

text: Joan's first mission was to join a convoy assembling at Blois, under the command of Marshal Jean de La Brosse, Lord of Boussac bringing supplies to Orléans. It was from Blois that Joan dispatched her famous missives to the English siege commanders, calling herself "the Maiden" ("La Pucelle"), and ordering them, in the name of God, to "Begone, or I will make you go".


title: Siege of Orléans

text: The relief convoy, escorted by some 400–500 soldiers, finally left Blois on 27 or 28 April, in nearly religious processional array. Joan had insisted on approaching Orléans from the north (through the Beauce region), where English forces were concentrated, intent on fighting them immediately. But the commanders decided to take the convoy in a circuitous route around the south (through the Sologne region) without telling Joan, reaching the south bank of the Loire at Rully (near Chécy), some four miles east of the city. Orléans' commander, Jean de Dunois, came out to meet them across the river. Joan was indignant at the deception and ordered an immediate attack on St. Jean-le-Blanc, the nearest English bastille on the south bank. But Dunois, supported by the Marshals, protested and with some effort, finally prevailed on her to allow the city to be resupplied before any assaults on anything. The provisions convoy approached the landing of Port Saint-Loup, across the river from the English bastille of Saint-Loup on the north bank. While French skirmishers kept the English garrison of Saint-Loup contained, a fleet of boats from Orléans sailed down to the landing to pick up the supplies, Joan and 200 soldiers. One of Joan's reputed miracles was said to have taken place here: the wind which had brought the boats upriver suddenly reversed itself, allowing them to sail back to Orléans smoothly under the cover of darkness. Joan of Arc entered Orléans in triumph on 29 April around 8:00 PM, to much rejoicing. The rest of the convoy returned to Blois.


title: Siege of Orléans

text: Over the next couple of days, to boost morale, Joan periodically toured the streets of Orléans, distributing food to the people and salaries to the garrison. Joan of Arc also sent out messengers to the English bastions demanding their departure, which the English commanders greeted with jeers. Some even threatened to kill the messengers as "emissaries of a witch".


title: Siege of Orléans

text: The "Journal du siege d'Orléans", as quoted in Pernoud, reports several discussions during the course of the following week between Joan and Jean de Dunois, the illegitimate half-brother of the Duke of Orléans and the chief leader directing the city's defense on behalf of the captive duke.


title: Siege of Orléans

text: Believing the garrison too small for any action, on 1 May Dunois left the city in the hands of La Hire and made his way personally to Blois to arrange for reinforcements. During this interlude, Joan went outside the city walls and surveyed all of the English fortifications personally, at one point exchanging words with the English commander William Glasdale.


title: Siege of Orléans

text: On 3 May Dunois's reinforcement convoy left Blois to head for Orléans. At the same time, other troop convoys set out from Montargis and Gien in the direction of Orléans. Dunois's military convoy arrived via the Beauce district, on the north bank of the river, in the early morning of 4 May, in full view of the English garrison at St. Laurent. The English declined to challenge the convoy's entry on account of its strength. Joan rode out to escort it in.


title: Siege of Orléans

text: At noon that day, 4 May 1429, apparently to secure the entry of more provisions convoys, which had taken the usual circuitous route via the east, Dunois launched an attack on the easterly English bastille of St. Loup together with the Montargis-Gien troops. Joan nearly missed out on it, having been napping when the assault began, but she hurried to join in. The English garrison of 400 was heavily outnumbered by the 1,500 French attackers. Hoping to divert the French away, the English commander, Lord John Talbot, launched an attack from St. Pouair, on the northern end of Orléans, but it was held back by a French sortie. After a few hours, St. Loup fell, with some 140 English killed and 40 prisoners taken. Some of the English defenders of St. Loup were captured in the ruins of a nearby church, their lives spared at Joan's request. Hearing that St. Loup had fallen, Talbot retired the northern assault.


title: Siege of Orléans

text: The next day, 5 May, was Ascension Day, and Joan urged an attack on the largest English outwork, the bastille of St. Laurent to the west. But the French captains, knowing its strength and that their men needed rest, prevailed on her to allow them to honor the feast-day in peace.


title: Siege of Orléans

text: The operation began in the early morning of 6 May. The citizens of Orléans, inspired by Joan of Arc, raised urban militias on her behalf and showed up at the gates, much to the distress of the professional commanders. Nonetheless, Joan prevailed upon the professionals to allow the militia to join. The French crossed the river from Orléans on boats and barges and landed on the island of St. Aignan, crossing over to the south bank via a makeshift pontoon bridge, landing on the stretch between the bridge complex and the bastille of St. Jean-le-Blanc. That plan had been to cut off and take St. Jean-le-Blanc from the west, but the English garrison commander, William Glasdale, sensing the intent of the French operation, had already hurriedly destroyed the St. Jean-le-Blanc outwork and concentrated his troops in the central Boulevart-Tourelles-Augustines complex.


title: Siege of Orléans

text: Before the French had properly disembarked on the south bank, La Hire reportedly launched a precipitous attack on the strongpoint of the Boulevart (an outlying fortification to the south of Les Tourelles). This nearly turned into a disaster, as the assault was exposed on the flanks to English fire from the Augustines. The assault broke off when there were cries that the English garrison of the bastille of St. Privé further west was rushing upriver to reinforce Glasdale and cut them off. Panic set in, and the French attackers retreated from the Boulevart back to the landing grounds, dragging Joan back with them. Seeing the "witch" on the run and the "spell" broken, Glasdale's garrison burst out to give chase, but according to legend, Joan turned around on them alone, raised her holy standard and cried out ""Au Nom De Dieu"" ("In the name of God"), which reportedly was sufficient to impress the English to halt their pursuit and return to the Boulevart. The fleeing French troops turned around and rallied to her.


title: Siege of Orléans

text: French commanders then launched an assault against the fortified monastery of "Les Augustins", which was finally taken just before nightfall.


title: Siege of Orléans

text: With the Augustins in French hands, Glasdale's garrison was blockaded in the Tourelles complex. That same night, what remained of the English garrison at St. Privé evacuated their outwork and went north of the river to join their comrades in St. Laurent. Glasdale was isolated, but he could count on a strong and well-ensconced English garrison of 700–800 troops.


title: Siege of Orléans

text: Joan had been wounded in the foot by stepping on a metal spike during the assault on the Augustins, and taken back to Orléans overnight to recover, and as a result did not participate in the evening war council. The next morning, 7 May, she was asked to sit out the final assault on the Boulevart-Tourelles, but she refused and roused to join the French camp on the south bank, much to the joy of the people of Orléans. The citizens raised more levies on her behalf and set about repairing the bridge with beams to enable a two-sided attack on the complex. Artillery was positioned on the island of Saint-Antoine.


title: Siege of Orléans

text: Early in the morning, Joan was struck down while standing in the trench to the south of Les Tourelles, by a longbow arrow between the neck and left shoulder and was hurriedly taken away. Rumors of her death bolstered the English defenders and faltered French morale. But, according to eyewitnesses, she returned later during the evening and told the soldiers that a final assault would carry the fortress. Joan's confessor / chaplain, Jean Pasquerel, later stated that Joan herself had some type of premonition or foreknowledge of her wound, stating the day before the attack that "tomorrow blood will flow from my body above my breast." Further assaults against Les Tourelles during the day were beaten back. As evening was approaching, Jean de Dunois had decided to leave the final assault for the next day. Informed of the decision, Joan went off for a period of quiet prayer, then returned to the area south of Les Tourelles, telling the troops that when her banner touched the fortress wall the place would be theirs. When one soldier shouted "It's touching! [the wall]", Joan replied ""Tout est vostre – et y entrez!"" ("All is yours, – go in!"). The French soldiery rushed in, swarming up the ladders into the fortification.


title: Siege of Orléans

text: The French carried the day and forced the English out of the boulevart and back into the last redoubt of the Tourelles. But the drawbridge connecting them gave way, and Glasdale fell into the river and perished. The French pressed on to storm the Tourelles itself, from both sides (the bridge now repaired). The Tourelles, half-burning, was finally taken in the evening.


title: Siege of Orléans

text: English losses were heavy. Counting other actions on the day (notably the interception of reinforcements rushed to the defense), the English had suffered nearly a thousand killed, and 600 prisoners. 200 French prisoners were found in the complex and released.


title: Siege of Orléans

text: With the Tourelles complex taken, the English had lost the south bank of the Loire. There was little point of continuing the siege, as Orléans could now be easily re-supplied indefinitely.


title: Siege of Orléans

text: On the morning of 8 May the English troops on the north bank, under the command of the Earl of Suffolk and Lord John Talbot, demolished their outworks and assembled in battle array in the field near St. Laurent. The French army under Dunois lined up before them. They stood facing each other immobile for about an hour, before the English withdrew from the field and marched off to join other English units in Meung, Beaugency and Jargeau. Some of the French commanders urged an attack to destroy the English army then and there. Joan of Arc reportedly forbade it, on account of it being Sunday.


title: Siege of Orléans

text: The English did not consider themselves beaten. Although they had suffered a setback and immense losses at Orléans itself, the surrounding perimeter of the Orleanais region – Beaugency, Meung, Janville, Jargeau – was still in their hands. Indeed, it was possible for the English to reorganize and resume the siege of Orléans itself soon after, this time perhaps with more success, as the bridge was now repaired, and thus more susceptible to being taken by assault. Suffolk's priority that day (8 May) was to salvage what remained of English arms.


title: Siege of Orléans

text: The French commanders realized as much, Joan less so. Leaving Orléans, she met the Dauphin Charles outside of Tours on 13 May to report her victory. She immediately called for a march northeast into Champagne, towards Reims, but the French commanders knew they had to first clear the English out of their dangerous positions on the Loire.


title: Siege of Orléans

text: The Loire Campaign began a couple of weeks later, after a period of rest and reinforcement. Volunteers of men and supplies swelled the French army, eager to serve under Joan of Arc's banner. Even the ostracized constable Arthur de Richemont was eventually permitted to join the campaign. After a series of brief sieges and battles at Jargeau (12 June), Meung (15 June) and Beaugency (17 June), the Loire was back in French hands. An English reinforcement army rushing from Paris under John Talbot was defeated at the Battle of Patay shortly after (18 June), the first significant field victory for French arms in years. The English commanders, the Earl of Suffolk and Lord Talbot, were taken prisoner in this campaign. Only thereafter did the French feel safe enough to accede to Joan's request for a march on Reims.


title: Siege of Orléans

text: After some preparation, the march on Reims began from Gien on 29 June, the Dauphin Charles following Joan and the French army through the dangerous Burgundian-occupied territory of Champagne. Although Auxerre (1 July) closed its gates and refused them entry, Saint-Florentin (3 July) yielded, as did, after some resistance, Troyes (11 July) and Châlons-sur-Marne (15 July). They reached Reims the next day and the Dauphin Charles, with Joan at his side, was finally consecrated as King Charles VII of France on 17 July 1429.


title: Siege of Orléans

text: The city of Orléans commemorates the lifting of the siege with an annual festival, including both modern and medieval elements and a woman representing Joan of Arc in full armor atop a horse. On 8 May Orléans simultaneously celebrates the lifting of the siege and V-E Day (Victory in Europe, the day that Nazi Germany surrendered to the Allies to end World War II in Europe.)


title: Optical disc drive

text: In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from certain discs, but recent drives can both read and record, also called burners or writers (since they physically burn the organic dye on write-once CD-R, DVD-R and BD-R LTH discs). Compact discs, DVDs, and Blu-ray discs are common types of optical media which can be read and recorded by such drives.


title: Optical disc drive

text: , most of the optical disc drives on the market are DVD-ROM drives and BD-ROM drives which read and record from those formats, along with having backward compatibility with CD, CD-R and CD-ROM discs; compact disc drives are no longer manufactured outside of audio devices. Read-only DVD and Blu-ray drives are also manufactured, but are less commonly found in the consumer market and mainly limited to media devices such as game consoles and disc media players. Over the last ten years, laptop computers no longer come with optical disc drives in order to reduce costs and make devices lighter, requiring consumers to purchase external optical drives.


title: Optical disc drive

text: Optical disc drives are an integral part of standalone appliances such as CD players, DVD players, Blu-ray Disc players, DVD recorders, certain desktop video game consoles, such as Sony PlayStation 4, Microsoft Xbox One, Nintendo Wii U, Sony PlayStation 5 and Xbox Series X and also in older consoles, such as the Sony PlayStation 3 and Xbox 360, and certain portable video game consoles, such as Sony PlayStation Portable (using proprietary now discontinued UMDs). They are also very commonly used in computers to read software and media distributed on disc and to record discs for archival and data exchange purposes. Floppy disk drives, with capacity of 1.44 MB, have been made obsolete: optical media are cheap and have vastly higher capacity to handle the large files used since the days of floppy discs, and the vast majority of computers and much consumer entertainment hardware have optical writers. USB flash drives, high-capacity, small, and inexpensive, are suitable where read/write capability is required.


title: Optical disc drive

text: Disc recording is restricted to storing files playable on consumer appliances (films, music, etc.), relatively small volumes of data (e.g. a standard DVD holds 4.7 gigabytes, however, higher-capacity formats such as multi-layer Blu-ray Discs exist) for local use, and data for distribution, but only on a small scale; mass-producing large numbers of identical discs by pressing (replication) is cheaper and faster than individual recording (duplication).


title: Optical disc drive

text: Optical discs are used to back up relatively small volumes of data, but backing up of entire hard drives, which typically contain many hundreds of gigabytes or even multiple terabytes, is less practical. Large backups are often instead made on external hard drives, as their price has dropped to a level making this viable; in professional environments magnetic tape drives are also used.


title: Optical disc drive

text: Some optical drives also allow predictively scanning the surface of discs for errors and detecting poor recording quality.


title: Optical disc drive

text: With an option in the optical disc authoring software, optical disc writers are able to simulate the writing process on CD-R, CD-RW, DVD-R and DVD-RW, which allows for testing such as observing the writing speeds and patterns (e.g. constant angular velocity, constant linear velocity and P-CAV and Z-CLV variants) with different writing speed settings and testing the highest capacity of an individual disc that would be achievable using overburning, without writing any data to the disc.


title: Optical disc drive

text: Few optical drives allow simulating a FAT32 flash drive from optical discs containing ISO9660/Joliet and UDF file systems or audio tracks (simulated as codice_1 files), for compatibility with most USB multimedia appliances.


title: Optical disc drive

text: Optical drives for computers come in two main form factors: "half-height" (also known as "desktop drive") and "slim type" (used in laptop computers and compact desktop computers). They exist as both internal and external variants.


title: Optical disc drive

text: "Half-height" optical drives are around 4 centimetres tall, while "slim type" optical drives are around 1 cm tall.


title: Optical disc drive

text: "Half-height" optical drives operate upwards of twice the speeds as "slim type" optical drives, because speeds on slim type optical drives are constrained to the physical limitations of the drive motor's rotation speed (around 5000rpm) rather than the performance of the optical pickup system.


title: Optical disc drive

text: Because "half-height" demand much more electrical power and a voltage of 12 V DC, while "slim" optical drives run on 5 volts, external "half height" optical drives require separate external power input, while external "slim type" are usually able to operate entirely on power delivered through a computer's USB port. Half height drives are also faster than Slim drives due to this, since more power is required to spin the disc at higher speeds.


title: Optical disc drive

text: "Half-height" optical drives hold discs in place from both sides while "slim type" optical drives fasten the disc from the bottom.


title: Optical disc drive

text: Half height drives fasten the disc using 2 spindles containing a magnet each, one under and one above the disc tray. The spindles may be lined with flocking or a texturized silicone material to exert friction on the disc, to keep it from slipping. The upper spindle is left slightly loose and is attracted to the lower spindle because of the magnets they have. When the tray is opened, a mechanism driven by the movement of the tray pulls the lower spindle away from the upper spindle and vice versa when the tray is closed. When the tray is closed, the lower spindle touches the inner circumference of the disc, and slightly raises the disc from the tray to the upper spindle, which is attracted to the magnet on the lower disc, clamping the disc in place. Only the lower spindle is motorized. Trays in half height drives often fully open and close using a motorized mechanism that can be pushed to close, controlled by the computer, or controlled using a button on the drive. Trays on half height and slim drives can also be locked by whatever program is using it, however it can still be ejected by inserting the end of a paper clip into an emergency eject hole on the front of the drive. Early CD players such as the Sony CDP-101 used a separate motorized mechanism to clamp the disc to the motorized spindle.


title: Optical disc drive

text: Slim drives use a special spindle with spring loaded specially shaped studs that radiate outwards, pressing against the inner edge of the disc. The user has to put uniform pressure onto the inner circumference of the disc to clamp it to the spindle and pull from the outer circumference while placing the thumb on the spindle to remove the disc, flexing it slightly in the process and returning to its normal shape after removal. The outer rim of the spindle may have a texturized silicone surface to exert friction keeping the disc from slipping. In slim drives most if not all components are on the disc tray, which pops out using a spring mechanism that can be controlled by the computer. These trays cannot close on their own; they have to be pushed until the tray reaches a stop.


title: Optical disc drive

text: The most important part of an optical disc drive is an "optical path", which is inside a "pickup head" ("PUH"). The PUH is also known as a laser pickup, optical pickup, pickup, pickup assembly, laser assembly, laser optical assembly, optical pickup head/unit or optical assembly. It usually consists of a semiconductor laser diode, a lens for focusing the laser beam, and photodiodes for detecting the light reflected from the disc's surface.


title: Optical disc drive

text: Initially, CD-type lasers with a wavelength of 780 nm (within the infrared) were used. For DVDs, the wavelength was reduced to 650 nm (red color), and for Blu-ray Disc this was reduced even further to 405 nm (violet color).


title: Optical disc drive

text: Two main servomechanisms are used, the first to maintain the proper distance between lens and disc, to ensure the laser beam is focused as a small "laser spot" on the disc. The second servo moves the pickup head along the disc's radius, keeping the beam on the "track", a continuous spiral data path. Optical disc media are 'read' beginning at the inner radius to the outer edge.


title: Optical disc drive

text: Near the laser lens, optical drives are usually equipped with one to three tiny potentiometers (usually separate ones for CDs, DVDs, and usually a third one for Blu-ray Discs if supported by the drive) that can be turned using a fine screwdriver. The potentiometer is in a series circuit with the laser lens and can be used to manually increase and decrease the laser power for repair purposes.


title: Optical disc drive

text: The laser diode used in DVD writers can have powers of up to 100 milliwatts, such high powers are used during writing. Some CD players have automatic gain control (AGC) to vary the power of the laser to ensure reliable playback of CD-RW discs.


title: Optical disc drive

text: Readability (the ability to read physically damaged or soiled discs) may vary among optical drives due to differences in optical pickup systems, firmwares, and damage patterns.


title: Optical disc drive

text: On factory-pressed "read only media" (ROM), during the manufacturing process the tracks are formed by pressing a thermoplastic resin into a nickel stamper that was made by plating a glass 'master' with raised 'bumps' on a flat surface, thus creating "pits" and "lands" in the plastic disk. Because the depth of the pits is approximately one-quarter to one-sixth of the laser's wavelength, the reflected beam's phase is shifted in relation to the incoming beam, causing mutual destructive interference and reducing the reflected beam's intensity. This is detected by photodiodes that create corresponding electrical signals.


title: Optical disc drive

text: An optical disk recorder encodes (also known as burning, since the dye layer is permanently burned) data onto a recordable CD-R, DVD-R, DVD+R, or BD-R disc (called a "blank") by selectively heating (burning) parts of an organic dye layer with a laser.


title: Optical disc drive

text: This changes the reflectivity of the dye, thereby creating marks that can be read like the pits and lands on pressed discs. For recordable discs, the process is permanent and the media can be written to only once. While the reading laser is usually not stronger than 5 mW, the writing laser is considerably more powerful. DVD lasers operate at voltages of around 2.5 volts.


title: Optical disc drive

text: The higher the writing speed, the less time a laser has to heat a point on the media, thus its power has to increase proportionally. DVD burners' lasers often peak at about 200 mW, either in continuous wave and pulses, although some have been driven up to 400 mW before the diode fails.


title: Optical disc drive

text: For rewritable CD-RW, DVD-RW, DVD+RW, DVD-RAM, or BD-RE media, the laser is used to melt a crystalline metal alloy in the recording layer of the disc. Depending on the amount of power applied, the substance may be allowed to melt back (change the phase back) into crystalline form or left in an amorphous form, enabling marks of varying reflectivity to be created.


title: Optical disc drive

text: "Double-sided" media may be used, but they are not easily accessed with a standard drive, as they must be physically turned over to access the data on the other side.


title: Optical disc drive

text: "Double layer" or "dual layer" (DL) media have two independent data layers separated by a semi-reflective layer. Both layers are accessible from the same side, but require the optics to change the laser's focus. Traditional "single layer" (SL) writable media are produced with a spiral groove molded in the protective polycarbonate layer (not in the data recording layer), to lead and synchronize the speed of recording head. Double-layered writable media have: a first polycarbonate layer with a (shallow) groove, a first data layer, a semi-reflective layer, a second (spacer) polycarbonate layer with another (deep) groove, and a second data layer. The first groove spiral usually starts on the inner edge and extends outwards, while the second groove start on the outer edge and extends inwards.


title: Optical disc drive

text: Some drives support Hewlett-Packard's LightScribe, or the alternative LabelFlash photothermal printing technology for labeling specially coated discs.


title: Optical disc drive

text: Zen Technology and Sony have developed drives that use several laser beams simultaneously to read discs and write to them at higher speeds than what would be possible with a single laser beam. The limitation with a single laser beam comes from wobbling of the disc that may occur at high rotational speeds; at 25,000 RPMs CDs become unreadable while Blu-rays cannot be written to beyond 5,000 RPMs. With a single laser beam, the only way to increase read and write speeds without reducing the pit length of the disc (which would allow for more pits and thus bits of data per revolution, but may require smaller wavelength light) is by increasing the rotational speed of the disc which reads more pits in less time, increasing data rate; hence why faster drives spin the disc at higher speeds. In addition, CDs at 27,500 RPMs (such as to read the inside of a CD at 52x) may explode causing extensive damage to the disc's surroundings, and poor quality or damaged discs may explode at lower speeds.


title: Optical disc drive

text: In Zen's system (developed in conjunction with Sanyo and licensed by Kenwood), a diffraction grating is used to split a laser beam into 7 beams, which are then focused into the disc; a central beam is used for focusing and tracking the groove of the disc leaving 6 remaining beams (3 on either side) that are spaced evenly to read 6 separate portions of the groove of the disc in parallel, effectively increasing read speeds at lower RPMs, reducing drive noise and


title: Optical disc drive

text: stress on the disc. The beams then reflect back from the disc, and are collimated and projected into a special photodiode array to be read. The first drives using the technology could read at 40x, later increasing to 52x and finally 72x. It uses a single optical pickup.


title: Optical disc drive

text: In Sony's system (used on their proprietary Optical Disc Archive system which is based on Archival Disc, itself based on Blu-ray) the drive has 4 optical pickups, two on each side of the disc, with each pickup having two lenses for a total of 8 lenses and laser beams. This allows for both sides of the disc to be read and written to at the same time, and for the contents of the disc to be verified during writing.


title: Optical disc drive

text: The rotational mechanism in an optical drive differs considerably from that of a hard disk drive's, in that the latter keeps a constant angular velocity (CAV), in other words a constant number of revolutions per minute (RPM). With CAV, a higher throughput is generally achievable at the outer disc compared to the inner.


title: Optical disc drive

text: On the other hand, optical drives were developed with an assumption of achieving a constant throughput, in CD drives initially equal to 150 KiB/s. It was a feature important for streaming audio data that always tend to require a constant bit rate. But to ensure no disc capacity was wasted, a head had to transfer data at a maximum linear rate at all times too, without slowing on the outer rim of the disc. This led to optical drives—until recently—operating with a constant linear velocity (CLV). The spiral "groove" of the disc passed under its head at a constant speed. The implication of CLV, as opposed to CAV, is that disc angular velocity is no longer constant, and the spindle motor needed to be designed to vary its speed from between 200 RPM on the outer rim and 500 RPM on the inner, keeping the data rate constant.


title: Optical disc drive

text: Later CD drives kept the CLV paradigm, but evolved to achieve higher rotational speeds, popularly described in multiples of a base speed. As a result, a 4× CLV drive, for instance, would rotate at 800-2000 RPM, while transferring data steadily at 600 KiB/s, which is equal to 4 × 150 KiB/s.


title: Optical disc drive

text: For DVDs, base or 1× speed is 1.385 MB/s, equal to 1.32 MiB/s, approximately nine times faster than the CD base speed. For Blu-ray drives, base speed is 6.74 MB/s, equal to 6.43 MiB/s.


title: Optical disc drive

text: Because keeping a constant transfer rate for the whole disc is not so important in most contemporary CD uses, a pure CLV approach had to be abandoned to keep the rotational speed of the disc safely low while maximizing data rate. Some drives work in a partial CLV (PCLV) scheme, by switching from CLV to CAV only when a rotational limit is reached. But switching to CAV requires considerable changes in hardware design, so instead most drives use the zoned constant linear velocity (Z-CLV) scheme. This divides the disc into several zones, each having its own constant linear velocity. A Z-CLV recorder rated at "52×", for example, would write at 20× on the innermost zone and then progressively increase the speed in several discrete steps up to 52× at the outer rim. Without higher rotational speeds, increased read performance may be attainable by simultaneously reading more than one point of a data groove, also known as "multi-beam", but drives with such mechanisms are more expensive, less compatible, and very uncommon.


title: Optical disc drive

text: Both DVDs and CDs have been known to explode when damaged or spun at excessive speeds. This imposes a constraint on the maximum safe speeds (56× CAV for CDs or around 18×CAV in the case of DVDs) at which drives can operate.


title: Optical disc drive

text: The reading speeds of most half-height optical disc drives released since circa 2007 are limited to ×48 for CDs, ×16 for DVDs and ×12 (angular velocities) for Blu-ray Discs. Writing speeds on selected write-once media are higher.


title: Optical disc drive

text: Some optical drives additionally throttle the reading speed based on the contents of optical discs, such as max. 40× CAV (constant angular velocity) for the Digital Audio Extraction ("“DAE”") of Audio CD tracks, 16× CAV for Video CD contents and even lower limitations on earlier models such as 4× CLV (constant linear velocity) for Video CDs.


title: Optical disc drive

text: Current optical drives use either a "tray-loading" mechanism, where the disc is loaded onto a motorized (as utilized by half-height, ""desktop"" drives) tray, a manually operated tray (as utilized in laptop computers, also called "slim type"), or a "slot-loading" mechanism, where the disc is slid into a slot and drawn in by motorized rollers. Slot-loading optical drives exist in both half-height (desktop) and slim type (laptop) form factors.


title: Optical disc drive

text: With both types of mechanisms, if a CD or DVD is left in the drive after the computer is turned off, the disc cannot be ejected using the normal eject mechanism of the drive. However, tray-loading drives account for this situation by providing a small hole where one can insert a paperclip to manually open the drive tray to retrieve the disc.


title: Optical disc drive

text: Slot-loading optical disc drives are prominently used in game consoles and vehicle audio units. Although allowing more convenient insertion, those have the disadvantages that they cannot usually accept the smaller 80 mm diameter discs (unless 80 mm optical disc adapter is used) or any non-standard sizes, usually have no emergency eject hole or eject button, and therefore have to be disassembled if the optical disc cannot be ejected normally. However, some slot-loading optical drives have been engineered to support miniature discs. The Nintendo Wii, because of backward compatibility with Nintendo GameCube games, and PlayStation 3 video game consoles are able to load both standard size DVDs and 80 mm discs in the same slot-loading drive. Its successor's slot drive however, the Wii U, lacks miniature disc compatibility.


title: Optical disc drive

text: There were also some early CD-ROM drives for desktop PCs in which its tray-loading mechanism will eject slightly and user has to pull out the tray manually to load a CD, similar to the tray ejecting method used in internal optical disc drives of modern laptops and modern external slim portable optical disc drives. Like the top-loading mechanism, they have spring-loaded ball bearings on the spindle.


title: Optical disc drive

text: A small number of drive models, mostly compact portable units, have a "top-loading" mechanism where the drive lid is manually opened upwards and the disc is placed directly onto the spindle (for example, all PlayStation One consoles, PlayStation 2 Slim, PlayStation 3 Super Slim, Nintendo GameCube consoles, Nintendo Wii Mini, most portable CD players, and some standalone CD recorders feature top-loading drives). These sometimes have the advantage of using spring-loaded ball bearings to hold the disc in place, minimizing damage to the disc if the drive is moved while it is spun up.


title: Optical disc drive

text: Unlike tray and slot loading mechanisms by default, top-load optical drives can be opened without being connected to power.


title: Optical disc drive

text: Some early CD-ROM drives used a mechanism where CDs had to be inserted into special cartridges or caddies, somewhat similar in appearance to a 3.5 inch micro floppy diskette. This was intended to protect the disc from accidental damage by enclosing it in a tougher plastic casing, but did not gain wide acceptance due to the additional cost and compatibility concerns—such drives would also inconveniently require "bare" discs to be manually inserted into an openable caddy before use. Ultra Density Optical ("UDO"), Magneto-optical drives, Universal Media Disc ("UMD"), DataPlay, Professional Disc, MiniDisc, Optical Disc Archive as well as early DVD-RAM and Blu-ray discs use optical disc cartridges.


title: Optical disc drive

text: All optical disc-drives use the SCSI-protocol on a command bus level, and initial systems used either a fully featured SCSI bus or as these were some what cost-prohibitive to sell to consumer applications, a proprietary cost-reduced version of the bus. This is because conventional ATA-standards at the time did not support, or have any provisions for any sort of removable media or hot-plugging of disk drives. Most modern internal drives for personal computers, servers, and workstations are designed to fit in a standard -inch (also written as 5.25 inch) drive bay and connect to their host via an ATA or SATA bus interface, but communicate using the SCSI protocol commands on software level as per the ATA Package Interface standard developed for making Parallel ATA/IDE interfaces compatible with removable media. Some devices may support vendor-specific commands such as recording density ("GigaRec"), laser power setting ("VariRec"), ability to manually hard-limit rotation speed in a way that overrides the universal speed setting (separately for reading and writing), and adjusting the lens and tray movement speeds where a lower setting reduces noise, as implmenented on some Plextor drives, as well as the ability to force overspeed burning, meaning beyond speed recommended for the media type, for testing purposes, as implemented on some Lite-On drives. Additionally, there may be digital and analog outputs for audio. The outputs may be connected via a header cable to the sound card or the motherboard or to headphones or an external speaker with a 3.5mm AUX plug cable that many early optical drives are equipped with. At one time, computer software resembling CD players controlled playback of the CD. Today the information is extracted from the disc as digital data, to be played back or converted to other file formats.


title: Optical disc drive

text: Some early optical drives have dedicated buttons for CD playback controls on their front panel, allowing them to act as a standalone compact disc player.


title: Optical disc drive

text: External drives were popular in the beginning, because the drives often required complex electronics to institute, rivaling in complexity the Host computer system itself. External drives using SCSI, Parallel port, USB and FireWire interfaces exist, most modern drives being USB. Some portable versions for laptops power themselves from batteries or directly from their interface bus.


title: Optical disc drive

text: Drives with a SCSI interface were originally the only system interface available, but they never became popular in the price sensitive low-end consumer market which constituted majority of the demand. They were less common and tended to be more expensive, because of the cost of their interface chipsets, more complex SCSI connectors, and small volume of sales in comparison to proprietary cost-reduced applications, but most importantly because most consumer market computer systems did not have any sort of SCSI interface in them the market for them was small. However, support for multitude of various cost-reduced proprietary optical drive bus standards were usually embedded with sound cards which were often bundled with the optical drives themselves in the early years. Some sound card and optical drive bundles even featured a full SCSI bus. Modern IDE/ATAPI compliant Parallel ATA and Serial ATA drive control chipsets and their interface technology is more complex to manufacture than a traditional 8bit 50Mhz SCSI drive interface, because they feature properties of both the SCSI and ATA bus, but are cheaper to make overall due to economies of scale.


title: Optical disc drive

text: When the optical disc drive was first developed, it was not easy to add to computer systems. Some computers such as the IBM PS/2 were standardizing on the -inch floppy and -inch hard disk and did not include a place for a large internal device. Also IBM PCs and clones at first only included a single (parallel) ATA drive interface, which by the time the CD-ROM was introduced, was already being used to support two hard drives and were completely incapable of supporting removable media, a drive falling off or being removed from the bus while the system was live, would cause an unrecoverable error and crash the entire system. Early consumer grade laptops simply had no built-in high-speed interface for supporting an external storage device. High-end workstation systems and laptops featured a SCSI interface which had a standard for externally connected devices.


title: Optical disc drive

text: Due to lack of asynchrony in existing implementations, an optical drive encountering damaged sectors may cause computer programs trying to access the drives, such as Windows Explorer, to lock up.


title: Optical disc drive

text: Drive models may support adjustment of behavioural parameters for performance optimization and testing purposes, such as the read retry count (codice_2), write retry count (codice_3), and the option to deactivate error correction (codice_4). For example, the read retry count specifies how often the drive should attempt reading a damaged sector. A higher value may increase the chance of successfully reading individual damaged sectors, but at the expense of responsiveness, since it adds delays during which the device seems unresponsive to the computer.


title: Optical disc drive

text: The codice_5 command-line utility allows manually controlling such parameters. For example, codice_6 sets the read retry count to 10 for the optical drive device file "sr0", and codice_7 lists all code pages. The values may be interpreted varyingly among drive models or vendors.


title: Optical disc drive

text: The optical drives in the photos are shown right side up; the disc would sit on top of them. The laser and optical system scans the underside of the disc.


title: Optical disc drive

text: With reference to the top photo, just to the right of image center is the disc motor, a metal cylinder, with a gray centering hub and black rubber drive ring on top. There is a disc-shaped round clamp, loosely held inside the cover and free to rotate; it's not in the photo. After the disc tray stops moving inward, as the motor and its attached parts rise, a magnet near the top of the rotating assembly contacts and strongly attracts the clamp to hold and center the disc. This motor is an "outrunner"-style brushless DC motor which has an external rotor – every visible part of it spins.


title: Optical disc drive

text: Two parallel guide rods that run between upper left and lower right in the photo carry the "sled", the moving optical read-write head. As shown, this "sled" is close to, or at the position where it reads or writes at the edge of the disc. To move the "sled" during continuous read or write operations, a stepper motor rotates a leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the short gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew is the rod with evenly-spaced darker details; these are the helical grooves that engage a pin on the "sled".


title: Optical disc drive

text: In contrast, the mechanism shown in the second photo, which comes from a cheaply made DVD player, uses less accurate and less efficient brushed DC motors to both move the sled and spin the disc. Some older drives use a DC motor to move the sled, but also have a magnetic rotary encoder to keep track of the position. Most drives in computers use stepper motors.


title: Optical disc drive

text: The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise from residual imbalance when running fast. The soft shock mount grommets are just below the brass-colored screws at the four corners (the left one is obscured).


title: Optical disc drive

text: In the third photo, the components under the cover of the lens mechanism are visible. The two permanent magnets on either side of the lens holder as well as the coils that move the lens can be seen. This allows the lens to be moved up, down, forwards, and backwards to stabilize the focus of the beam.


title: Optical disc drive

text: In the fourth photo, the inside of the optics package can be seen. Note that since this is a CD-ROM drive, there is only one laser, which is the black component mounted to the bottom left of the assembly. Just above the laser are the first focusing lens and prism that direct the beam at the disc. The tall, thin object in the center is a half-silvered mirror that splits the laser beam in multiple directions. To the bottom right of the mirror is the main photodiode that senses the beam reflected off the disc. Above the main photodiode is a second photodiode that is used to sense and regulate the power of the laser.


title: Optical disc drive

text: The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "flexible circuits" that connect everything to the electronics (which is not shown).


title: Optical disc drive

text: The first laser disc, demonstrated in 1972, was the "Laservision" 12-inch video disc. The video signal was stored as an analog format like a video cassette. The first digitally recorded optical disc was a 5-inch audio compact disc (CD) in a read-only format created by Sony and Philips in 1975.


title: Optical disc drive

text: The first erasable optical disc drives were announced in 1983, by Matsushita (Panasonic), Sony, and Kokusai Denshin Denwa (KDDI). Sony eventually released the first commercial erasable and rewritable -inch optical disc drive in 1987, with dual-sided discs capable of holding 325 MB per side.


title: Optical disc drive

text: The CD-ROM format was developed by Sony and Denon, introduced in 1984, as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data. The CD-ROM format has a storage capacity of 650 MB. Also in 1984, Sony introduced a LaserDisc data storage format, with a larger data capacity of 3.28 GB.


title: Optical disc drive

text: In September 1992, Sony announced the MiniDisc format, which was supposed to combine the audio clarity of CD's and the convenience of a cassette size. The standard capacity holds 80 minutes of audio. In January 2004, Sony revealed an upgraded Hi-MD format, which increased the capacity to 1 GB (48 hours of audio).


title: Optical disc drive

text: The DVD format, developed by Panasonic, Sony, and Toshiba, was released in 1995, and was capable of holding 4.7 GB per layer; with the first DVD players shipping on November 1, 1996, by Panasonic and Toshiba in Japan and the first DVD-ROM compatible computers being shipped on November 6 of that year by Fujitsu. Sales of DVD-ROM drives for computers in the U.S. began on March 24, 1997, when Creative Labs released their PC-DVD kit to the market.


title: Optical disc drive

text: In 1999, Kenwood released a multi-beam optical drive that achieved burning speeds as high as 72×, which would require dangerous spinning speeds to attain with single-beam burning. However, it suffered from reliability issues.


title: Optical disc drive

text: The first Blu-ray prototype was unveiled by Sony in October 2000, and the first commercial recording device was released to market on April 10, 2003. In January 2005, TDK announced that they had developed an ultra-hard yet very thin polymer coating ("Durabis") for Blu-ray Discs; this was a significant technical advance because better protection was desired for the consumer market to protect bare discs against scratching and damage compared to DVD. Technically Blu-ray Disc also required a thinner layer for the narrower beam and shorter wavelength 'blue' laser. The first BD-ROM players (Samsung BD-P1000) were shipped in mid-June 2006. The first Blu-ray Disc titles were released by Sony and MGM on June 20, 2006. The first mass-market Blu-ray Disc rewritable drive for the PC was the BWU-100A, released by Sony on July 18, 2006.


title: Optical disc drive

text: Starting in the mid 2010s, computer manufacturers began to stop including built-in optical disc drives on their products, with the advent of cheap, rugged (scratches can not cause corrupted data, inaccessible files or skipping audio/video), fast and high capacity USB drives and video on demand over the internet. Excluding an optical drive allows for circuit boards in laptops to be larger and less dense, requiring less layers, reducing production costs while also reducing weight and thickness, or for batteries to be larger. Computer case manufacturers also began to stop including -inch bays for installing optical disc drives. However, new optical disc drives are still (as of 2020) available for purchase. Notable optical disc drive OEMs include Hitachi, LG Electronics (merged into Hitachi-LG Data Storage), Toshiba, Samsung Electronics (merged into Toshiba Samsung Storage Technology), Sony, NEC (merged into Optiarc), Lite-On, Philips (merged into Philips & Lite-On Digital Solutions), Pioneer Corporation, Plextor, Panasonic, Yamaha Corporation and Kenwood.


title: Optical disc drive

text: Most optical drives are backward compatible with their ancestors up to CD, although this is not required by standards.


title: Optical disc drive

text: Compared to a CD's 1.2 mm layer of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm in order to reach the recording surface. This allows a DVD drive to focus the beam on a smaller spot size and to read smaller pits. DVD lens supports a different focus for CD or DVD media with same laser. With the newer Blu-ray Disc drives, the laser only has to penetrate 0.1 mm of material. Thus the optical assembly would normally have to have an even greater focus range. In practice, the Blu-ray optical system is separate from the DVD/CD system.


title: Optical disc drive

text: During the times of CD writer drives, they are often marked with three different speed ratings. In these cases, the first speed is for write-once (R) operations, the second speed for re-write (RW) operations, and the last speed for read-only (ROM) operations. For example, a 40×/16×/48× CD writer drive is capable of writing to CD-R media at speed of 40× (6,000 kbit/s), writing to CD-RW media at speed of 16× (2,400 kbit/s), and reading from a CD-ROM media at speed of 48× (7,200 kbit/s).


title: Optical disc drive

text: During the times of combo (CD-RW/DVD-ROM) drives, an additional speed rating (e.g. the 16× in 52×/32×/52×/16×) is designated for DVD-ROM media reading operations.


title: Optical disc drive

text: For DVD writer drives, Blu-ray Disc combo drives, and Blu-ray Disc writer drives, the writing and reading speed of their respective optical media are specified in its retail box, user's manual, or bundled brochures or pamphlets.


title: Optical disc drive

text: In the late 1990s, "buffer underruns" became a very common problem as high-speed CD recorders began to appear in home and office computers, which—for a variety of reasons—often could not muster the I/O performance to keep the data stream to the recorder steadily fed. The recorder, should it run short, would be forced to halt the recording process, leaving a truncated track that usually renders the disc useless.


title: Optical disc drive

text: In response, manufacturers of CD recorders began shipping drives with "buffer underrun protection" (under various trade names, such as Sanyo's "BURN-Proof", Ricoh's "JustLink" and Yamaha's "Lossless Link"). These can suspend and resume the recording process in such a way that the gap the stoppage produces can be dealt with by the error-correcting logic built into CD players and CD-ROM drives. The first of these drives were rated at 12× and 16×.


title: Optical disc drive

text: The first optical drive to support recording DVDs at 16× speed was the Pioneer DVR-108, released in the second half of 2004. At that time however, no recordable DVD media supported that high recording speed yet.


title: Optical disc drive

text: While drives are burning DVD+R, DVD+RW and all Blu-ray formats, they do not require any such error correcting recovery as the recorder is able to place the new data exactly on the end of the suspended write effectively producing a continuous track (this is what the DVD+ technology achieved). Although later interfaces were able to stream data at the required speed, many drives now write in a 'zoned constant linear velocity' (""Z-CLV""). This means that the drive has to temporarily suspend the write operation while it changes speed and then recommence it once the new speed is attained. This is handled in the same manner as a buffer underrun.


title: Optical disc drive

text: The internal buffer of optical disc writer drives is: 8 MiB or 4 MiB when recording BD-R, BD-R DL, BD-RE, or BD-RE DL media; 2 MiB when recording DVD-R, DVD-RW, DVD-R DL, DVD+R, DVD+RW, DVD+RW DL, DVD-RAM, CD-R, or CD-RW media.


title: Optical disc drive

text: CD recording on personal computers was originally a batch-oriented task in that it required specialised authoring software to create an "image" of the data to record and to record it to disc in the one session. This was acceptable for archival purposes, but limited the general convenience of CD-R and CD-RW discs as a removable storage medium.


title: Optical disc drive

text: Packet writing is a scheme in which the recorder writes incrementally to disc in short bursts, or packets. Sequential packet writing fills the disc with packets from bottom up. To make it readable in CD-ROM and DVD-ROM drives, the disc can be "closed" at any time by writing a final table-of-contents to the start of the disc; thereafter, the disc cannot be packet-written any further. Packet writing, together with support from the operating system and a file system like UDF, can be used to mimic random write-access as in media like flash memory and magnetic disks.


title: Optical disc drive

text: Fixed-length packet writing (on CD-RW and DVD-RW media) divides up the disc into padded, fixed-size packets. The padding reduces the capacity of the disc, but allows the recorder to start and stop recording on an individual packet without affecting its neighbours. These resemble the block-writable access offered by magnetic media closely enough that many conventional file systems will work as-is. Such discs, however, are not readable in most CD-ROM and DVD-ROM drives or on most operating systems without additional third-party drivers. The division into packets is not as reliable as it may seem as CD-R(W) and DVD-R(W) drives can only locate data to within a data block. Although generous gaps (the padding referred to above) are left between blocks, the drive nevertheless can occasionally miss and either destroy some existing data or even render the disc unreadable.


title: Optical disc drive

text: The DVD+RW disc format eliminates this unreliability by embedding more accurate timing hints in the data groove of the disc and allowing individual data blocks (or even bytes) to be replaced without affecting backward compatibility (a feature dubbed "lossless linking"). The format itself was designed to deal with discontinuous recording because it was expected to be widely used in digital video recorders. Many such DVRs use variable-rate video compression schemes which require them to record in short bursts; some allow simultaneous playback and recording by alternating quickly between recording to the tail of the disc whilst reading from elsewhere. The Blu-ray Disc system also encompasses this technology.


title: Optical disc drive

text: Mount Rainier aims to make packet-written CD-RW and DVD+RW discs as convenient to use as that of removable magnetic media by having the firmware format new discs in the background and manage media defects (by automatically mapping parts of the disc which have been worn out by erase cycles to reserve space elsewhere on the disc). As of February 2007, support for Mount Rainier is natively supported in Windows Vista. All previous versions of Windows require a third-party solution, as does Mac OS X.


title: Optical disc drive

text: Owing to pressure from the music industry, as represented by the IFPI and RIAA, Philips developed the "Recorder Identification Code" (RID) to allow media to be uniquely associated with the recorder that has written it. This standard is contained in the Rainbow Books. The RID-Code consists of a supplier code (e.g. "PHI" for Philips), a model number and the unique ID of the recorder. Quoting Philips, the RID "enables a trace for each disc back to the exact machine on which it was made using coded information in the recording itself. The use of the RID code is mandatory."


title: Optical disc drive

text: Although the RID was introduced for music and video industry purposes, the RID is included on every disc written by every drive, including data and backup discs. The value of the RID is questionable as it is (currently) impossible to locate any individual recorder due to there being no database.


title: Optical disc drive

text: The Source Identification Code (SID) is an eight character supplier code that is placed on optical discs by the manufacturer. The SID identifies not only manufacturer, but also the individual factory and machine that produced the disc.


title: Optical disc drive

text: According to Phillips, the administrator of the SID codes, the SID code provides an optical disc production facility with the means to identify all discs mastered or replicated in its plant, including the specific Laser Beam Recorder (LBR) signal processor or mould that produced a particular stamper or disc.


title: Optical disc drive

text: The standard use of RID and SID mean that each disc written contains a record of the machine that produced a disc (the SID), and which drive wrote it (the RID). This combined knowledge may be very useful to law enforcement, to investigative agencies, and to private or corporate investigators.


title: Optical disc drive

text: A significant motivation for introducing the SID code was to identify disc manufacturing plants producing unauthorised copies of commercial CDs. By the 1990s, the production process for CDs had evolved from requiring a "clean-room" environment involving multiple processes, this demanding a substantial investment and likely to be confined to "responsible" organisations, into an activity that could be undertaken with "mono-liner" equipment, this having been developed in the late 1980s and capable of packaging "the whole process into a single box" that could occupy "no more space than a couple of office desks". Consequently, the CD manufacturing industry had grown to include less reputable organisations and, by 1994, could produce a volume of discs twice that of the estimated demand for "legitimate CDs", with music industry organisations claiming that illicit copies were outselling legitimate copies by significant margins in some markets. Philips and the IFPI envisaged that combinations of codes, each identifying a disc mastering establishment and the manufacturing plant used to make a particular disc, would assist in identifying those responsible for illicit CD production. However, the scheme relied on existing manufacturing plants upgrading their equipment to support the introduction of this measure, and the accompanying challenge of convincing such facilities was perceived as "a little difficult" in cases where those facilities were already involved in making considerable numbers of illicit discs.


"Thou shalt not bear false witness against thy neighbour" (Exodus 20:16) is one of the Ten Commandments, widely understood as moral imperatives by Jewish, Catholic, and Protestant scholars.


title: Thou shalt not bear false witness against thy neighbour

text: The Book of Exodus describes the Ten Commandments as being spoken by God, inscribed on two stone tablets by the finger of God, broken by Moses, and rewritten by Yahweh on a replacement set of stones hewn by Moses.


text: The command against false testimony is seen as a natural consequence of the command to “love your neighbour as yourself”. This moral prescription flows from the command for holy people to bear witness to their deity. Offenses against the truth express by word or deed a refusal to commit oneself to moral uprightness: they are fundamental infidelities to God and, in this sense, they undermine the foundations of covenant with God.


text: The Hebrew Bible contains a number of prohibitions against false witness, lying, spreading false reports, etc. For a person who had a charge brought against them and were brought before a religious prosecution, the charge was considered as established only on the evidence of two or three sworn witnesses. In cases where false testimony was suspected, the religious judges were to make a thorough investigation, and if false testimony were proven, the false witness was to receive the punishment he had intended to bring on the person falsely accused. For example, since murder was a capital crime, giving false testimony in a murder case was subject to the death penalty. Those eager to receive or listen to false testimony were also subject to punishment.


text: False witness is among the six things God hates, king Solomon says. False testimony is among the things that defile a person, Jesus says.


text: The witness who hid what he had seen or what he knew bore his iniquity; if he realized his guilt, he had to confess his sin, brought to the Lord a female lamb or goat from the flock (or two turtledoves or two pigeons, or a tenth of an ephah of fine flour) for a sin offering as his compensation for the sin he committed.


text: The lying witness is a deceitful man, who mocks at justice. He is like a war club, or a sword, or a sharp arrow. ″A false witness will not go unpunished.″ king Solomon says. ″A false witness will perish″ if he does not repent.


text: Some of those who belonged to the synagogue of the Freedmen and of the Cyrenians, and of the Alexandrians, and of those from Cilicia and Asia came upon Stephen and seized him and brought him before the council and set up false witnesses against him. These false witnesses said: "This man never ceases to speak words against this holy place (Temple of Jerusalem) and the law, for we have heard him say that this Jesus of Nazareth will destroy this place (Stephen said that the temple of Jesus′ body had been destroyed by others but raise it up by Him in three days, according with what Jesus had said ) and the customs that Moses delivered to us."(Stephen said what Jesus had said namely He had come to fulfil the Law of Moses and the Prophets) And gazing at him, all who sat in the council saw Stephen′ s face was like the face of an angel.


text: Many testified falsely against Jesus, but their statements did not agree. At last two witnesses said they had heard Him saying He would destroy that temple and in three days built another, not made with hands, (He really had meant the resurrection of His body, as a temple of the Holy Spirit, destroyed by others but raise it up by Him). Yet even about this their testimony did not agree.


text: The narrative in 1 Kings 21 describes a case of false testimony. King Ahab of Israel tried to convince Naboth the Jezreelite to sell him the vineyard Naboth owned adjacent to the king's palace. Ahab wanted the land to use as a vegetable garden, but Naboth refused to sell or trade the property to Ahab saying, “The forbid that I should give up to you what I have inherited from my fathers!” Ahab's wife Jezebel then conspired to obtain the vineyard by writing letters in Ahab's name to the elders and nobles in Naboth's town instructing them to have two scoundrels bear false witness claiming that Naboth has cursed both God and the king. After Naboth was subsequently stoned to death, Ahab seized possession of Naboth's vineyard. The text describes the as very angry with Ahab, and the prophet Elijah pronounces judgment on both Ahab and Jezebel.


text: The narrative in 2 Samuel 1 also contains a narrative which is often interpreted as false testimony. The 1 Samuel narrative had described Saul as killing himself by falling on his own sword after having been wounded by the Philistines on Mount Gilboa and being in a situation with no hope of victory or escape. However, 2 Samuel tells of an Amalekite, who was probably on Mount Gilboa to strip the dead of their possessions, appearing to David with Saul's crown and royal arm band and giving testimony that he had himself killed king Saul. David immediately ordered that the Amalekite be put to death, saying, "Your blood be on your head, for your own mouth has testified against you, saying, 'I have killed the ’s anointed.'" The truth of the Amalekite's testimony did not need to be determined for the sentence to be carried out: either the Amalekite had killed King Saul, or he had given false testimony to David regarding Saul's death. Both crimes were seen as equally deserving of the death penalty.


text: The ancient understanding of false testimony not only includes testifying with false words, but also failing to come forward with relevant testimony in response to a public charge. “If a person sins because he does not speak up when he hears a public charge to testify regarding something he has seen or learned about, he will be held responsible.”


text: Jewish law enumerates 613 Mitzvot or commandments, including several commandments related to honest testimony as related to judicial procedure.


text: Maimonides (the Rambam) further explained that if false testimony was calculated to occasion a monetary loss, the court should inflict a monetary loss of equal value on the false witness. Likewise, if the false testimony was calculated to result in death, the false witness is to suffer the same kind of death. In Sefer Hachinuch, one who fails to testify when one is aware of evidence is compared to one who stands idly by the blood of one's neighbor. The severity of breaking the ninth commandment is reflected in a midrash:


text: According to the New Testament, Jesus explains that obedience to the prohibition against false testimony from the ten commandments is a requirement for eternal life. According to Jesus, false testimony comes from the sinful desires of the heart and makes people unclean.


text: The New Testament narrative also describes several occasions where people testify falsely against Jesus and his disciples. When Jesus was on trial before the Sanhedrin, the chief priests were looking for evidence to justify putting Jesus to death, and the narrative in Matthew's Gospel states that many false witnesses () came forward. Jesus remained silent until the high priest charged him under oath to answer whether Jesus is “the Christ, the Son of God”. Jesus answered affirmatively.


text: The Acts of the Apostles describes the disciple Stephen being seized and brought before the Sanhedrin. Those who opposed Stephen persuaded false witnesses to testify that Stephen was guilty of blasphemy against Moses and against God. Stephen used the occasion of his trial to remind the Sanhedrin of the Old Testament testimony of rebellion, idolatry, and persecution of the prophets that culminated in the murder of Jesus. The crowd was so angry that Stephen was stoned to death.


text: The New Testament depicts the Apostles as being appointed as true witnesses to the ministry and resurrection of Jesus Christ. The Apostle Paul uses the Old Testament prohibition of false testimony to describe his fear of God if found to be a false witness about God regarding the resurrection.


text: In , Paul lists a number of the ten commandments which can be summed up in the saying "You shall love your neighbor as yourself". The Textus Receptus and the King James Bible include "You shall not bear false witness", but this commandment is missing from some early manuscripts containing Romans 13 and the Cambridge Bible for Schools and Colleges suggests that it is "perhaps to be omitted, on documentary evidence".


text: The Eastern Orthodox Christian is expected to uphold truth, at all times and in all places, without exception. Slander and gossip are equally evil, and the initial speaker is responsible for any further damage caused as the report is spread. Unless there is a compelling reason to speak ill of someone, as is the case of protect oneself or others against harm, it is not permissible even if the account be true. Saint Dorotheus of Gaza said, "You may well know about the sin, but you do not know about the repentance."


text: The Roman Catholic Church interprets the command against "false witness" more broadly than the Jewish historical context of perjury, and considers it as a broad prohibition against misrepresenting the truth in one's relation with others. This commandment enjoins truthfulness and respect for other's good name, even the dead. It prohibits detraction (true faults), calumny (false faults), gossip, rash judgment, lying, and the violation of secrets.


text: The "Catechism of the Catholic Church" (§2469) states, "...The virtue of truth gives another his just due. Truthfulness keeps to the just mean between what ought to be expressed and what ought to be kept secret: it entails honesty and discretion. In justice, "as a matter of honor, one man owes it to another to manifest the truth."


text: Catholic teaching describes truth as uprightness in human action and speech and is the virtue which consists of showing oneself true in deeds and truthful in words, and in guarding against duplicity, dissimulation, and hypocrisy. The person of truth gives another his just due. Truthfulness balances what ought to be expressed and what ought to be kept secret: it entails both honesty and discretion. In justice, one man owes it to another to manifest the truth. The disciple of Christ consents to "live in the truth," that is, in the simplicity of a life in conformity with the Lord's example, abiding in his truth. "If we say we have fellowship with him while we walk in darkness, we lie and do not live according to the truth."(1 John 1:6)


text: To keep “a clear conscience toward God and toward men”(Acts 24:16), Christians must follow Christ's example “to bear witness to the truth.”(John 18:37) The Christian is not to “be ashamed then of testifying to our Lord.”(2 Timothy 1:8) In situations that require witness to the faith, the Christian must profess it without equivocation. Christian witness to the Gospel and the obligations that flow from it are an act of justice that establishes the truth or makes it known. Catholic teaching regards martyrdom as the supreme witness given to the truth of the faith: it means bearing witness even unto death.


text: Christ's disciples have "put on the new man, created after the likeness of God in true righteousness and holiness."(Ephesians 4:24) By "putting away falsehood," they are to "put away all malice and all guile and insincerity and envy and all slander." (Ephesians 4:25, 1 Peter 2:1)


text: Public statements contrary to the truth take on a particular gravity. In court it becomes false witness. (Proverbs 19:9) False statements under oath are perjury. Acts such as these contribute to condemnation of the innocent, exoneration of the guilty, or the increased punishment of the accused. (Proverbs 18:5) These are great sins, because they gravely compromise the exercise of justice and the fairness of judicial decisions.


text: Respect for the reputation of persons forbids every attitude and word likely to cause unjust injury. One is guilty of rash judgment who assumes the moral fault of a neighbor without sufficient foundation. One is guilty of detraction who discloses another's faults and failings to persons who did not know them without objectively valid reason. One is guilty of calumny (a misrepresentation intended to harm another's reputation) who harms the reputation of others and gives occasion for false judgments concerning them by remarks contrary to the truth. These sins violate both the commandment against false witness, as well as the command to love one's neighbor as oneself.


text: Not only are gossip and slander held to be covered by the commandment against false witness, Catholic teaching also holds that “every word or attitude is forbidden which by flattery, adulation, or complaisance encourages and confirms another in malicious acts and perverse conduct. Adulation is a grave fault if it makes one an accomplice in another's vices or grave sins. Neither the desire to be of service nor friendship justifies duplicitous speech.” Furthermore, boasting and bragging are viewed as offenses against truth. So is irony aimed at disparaging someone by maliciously caricaturing (mocking) some aspect of his behavior.


text: The Catholic Church teaches that "A lie consists in speaking a falsehood with the intention of deceiving." According to the Bible, the Lord denounces lying as the work of the devil: "You are of your father the devil, . . . there is no truth in him. When he lies, he speaks according to his own nature, for he is a liar and the father of lies." (John 8:44) Lying is the most direct offense against the truth. To lie is to speak or act against the truth in order to lead someone into error. By injuring man's relation to truth and to his neighbor, a lie offends against the fundamental relation of man and of his word to the Lord. Lying is a mortal sin when it does grave injury to the virtues of justice and charity. Lying is a profanation of speech, whereas the purpose of speech is to communicate known truth to others. The deliberate intention of leading a neighbor into error by saying things contrary to the truth constitutes a failure in justice and charity. The culpability is greater when the intention of deceiving entails the risk of deadly consequences for those who are led astray. By violating the virtue of truthfulness, a lie does real violence to another. It affects his ability to know, which is a condition of every judgment and decision. It contains the seed of discord and all consequent evils. Lying is destructive of society; it undermines trust among men and tears apart the fabric of social relationships.


text: However, the right to the communication of the truth is not unconditional in Catholic teaching. Everyone must conform his life to the Gospel precept of fraternal love. In concrete situations one should judge whether it is appropriate to reveal the truth to someone who asks for it. Charity and respect for the truth should dictate the response to every request for information or communication. The good and safety of others, respect for privacy, and the common good are sufficient reasons for being silent about what ought not be known or for making use of a discreet language. The duty to avoid scandal often commands strict discretion. No one is bound to reveal the truth to someone who does not have the right to know it. The golden rule helps one discern, in concrete situations, whether it would be appropriate to reveal the truth to someone who asks for it. The sacrament of confession is inviolable.


text: Martin Luther explained that this commandment is given “first of all that every one shall help his neighbor to secure his rights, and not allow them to be hindered or twisted, but shall promote and strictly maintain them, no matter whether he be judge or witness.” Luther also asserted that this command extends to the spiritual jurisdiction and prohibited slander against preachers and Christians by calling them heretics, apostates, seditious, wicked, etc. Thirdly, he described the commandment against false witness to prohibit the public judgment and reproof of his neighbor. One can indeed see and hear the neighbor sin, but one has no command to report it to others. If one judges and passes sentence, one falls into a sin which is greater than his (except for judges, parents, and preachers.)


text: Slanderers are not content with knowing a thing, but “proceed to assume jurisdiction, and when they know a slight offense of another, carry it into every corner, and are delighted and tickled that they can stir up another's displeasure [baseness], as swine roll themselves in the dirt and root in it with the snout.” Luther describes this as meddling with the judgment and office of God, and pronouncing sentence and punishment with the most severe verdict. Without wielding the sword, the slanderer employs a poisonous tongue to the shame and hurt of your neighbor.


text: John Calvin taught that the commandment against false witness prohibits all calumnies (gossip and slander) and false accusations which might injure our neighbor's good name, and any falsehood which might impair his fortune. Christians must assert only the truth with pure motives for the maintenance of our neighbor's good name and estate.


text: Calvin asserted that God's intent in the prohibition of false witness extended “more generally to calumny and sinister insinuations by which our neighbors are unjustly aggrieved.” Since perjury in court is amply prohibited by the third commandment (against swearing falsely), the commandment against false witness must extend to protection of one's good name. “The equity of this is perfectly clear. For if a good name is more precious than riches, a man, in being robbed of his good name, is no less injured than if he were robbed of his goods; while, in the latter case, false testimony is sometimes not less injurious than rapine committed by the hand.”


text: Matthew Henry taught that the prohibition against false witness concerns our own and our neighbor's good name. “Thou shalt not bear false witness” forbids: “1. Speaking falsely in any matter, lying, equivocating, and any way devising and designing to deceive our neighbour. 2. Speaking unjustly against our neighbour, to the prejudice of his reputation; and (which involves the guilty of both). 3. Bearing false witness against him, laying to his charge things that he knows not, either judicially, upon oath (by which the third commandment, and the sixth and eighth, as well as this, are broken), or extrajudicially, in common converse, slandering, backbiting, tale-bearing, aggravating what is done amiss and making it worse than it is, and any way endeavouring to raise our own reputation upon the ruin of our neighbour’s."


title: Curve fitting

text: Curve fitting is the process of constructing a curve, or mathematical function, that has the best fit to a series of data points, possibly subject to constraints. Curve fitting can involve either interpolation, where an exact fit to the data is required, or smoothing, in which a "smooth" function is constructed that approximately fits the data. A related topic is regression analysis, which focuses more on questions of statistical inference such as how much uncertainty is present in a curve that is fit to data observed with random errors. Fitted curves can be used as an aid for data visualization, to infer values of a function where no data are available, and to summarize the relationships among two or more variables. Extrapolation refers to the use of a fitted curve beyond the range of the observed data, and is subject to a degree of uncertainty since it may reflect the method used to construct the curve as much as it reflects the observed data.


title: Curve fitting

text: For linear-algebraic analysis of data, "fitting" usually means trying to find the curve that minimizes the vertical ("y"-axis) displacement of a point from the curve (e.g., ordinary least squares). However, for graphical and image applications, geometric fitting seeks to provide the best visual fit; which usually means trying to minimize the orthogonal distance to the curve (e.g., total least squares), or to otherwise include both axes of displacement of a point from the curve. Geometric fits are not popular because they usually require non-linear and/or iterative calculations, although they have the advantage of a more aesthetic and geometrically accurate result.


title: Curve fitting

text: is a line with slope "a". A line will connect any two points, so a first degree polynomial equation is an exact fit through any two points with distinct x coordinates.


title: Curve fitting

text: A more general statement would be to say it will exactly fit four constraints. Each constraint can be a point, angle, or curvature (which is the reciprocal of the radius of an osculating circle). Angle and curvature constraints are most often added to the ends of a curve, and in such cases are called end conditions. Identical end conditions are frequently used to ensure a smooth transition between polynomial curves contained within a single spline. Higher-order constraints, such as "the change in the rate of curvature", could also be added. This, for example, would be useful in highway cloverleaf design to understand the rate of change of the forces applied to a car (see jerk), as it follows the cloverleaf, and to set reasonable speed limits, accordingly.


title: Curve fitting

text: The first degree polynomial equation could also be an exact fit for a single point and an angle while the third degree polynomial equation could also be an exact fit for two points, an angle constraint, and a curvature constraint. Many other combinations of constraints are possible for these and for higher order polynomial equations.


title: Curve fitting

text: If there are more than "n" + 1 constraints ("n" being the degree of the polynomial), the polynomial curve can still be run through those constraints. An exact fit to all constraints is not certain (but might happen, for example, in the case of a first degree polynomial exactly fitting three collinear points). In general, however, some method is then needed to evaluate each approximation. The least squares method is one way to compare the deviations.


title: Curve fitting

text: There are several reasons given to get an approximate fit when it is possible to simply increase the degree of the polynomial equation and get an exact match.:


title: Curve fitting

text: The degree of the polynomial curve being higher than needed for an exact fit is undesirable for all the reasons listed previously for high order polynomials, but also leads to a case where there are an infinite number of solutions. For example, a first degree polynomial (a line) constrained by only a single point, instead of the usual two, would give an infinite number of solutions. This brings up the problem of how to compare and choose just one solution, which can be a problem for software and for humans, as well. For this reason, it is usually best to choose as low a degree as possible for an exact match on all constraints, and perhaps an even lower degree, if an approximate fit is acceptable.


title: Curve fitting

text: Other types of curves, such as trigonometric functions (such as sine and cosine), may also be used, in certain cases.


title: Curve fitting

text: In biology, ecology, demography, epidemiology, and many other disciplines, the growth of a population, the spread of infectious disease, etc. can be fitted using the logistic function.


title: Curve fitting

text: In agriculture the inverted logistic sigmoid function (S-curve) is used to describe the relation between crop yield and growth factors. The blue figure was made by a sigmoid regression of data measured in farm lands. It can be seen that initially, i.e. at low soil salinity, the crop yield reduces slowly at increasing soil salinity, while thereafter the decrease progresses faster.


title: Curve fitting

text: Other types of curves, such as conic sections (circular, elliptical, parabolic, and hyperbolic arcs) or trigonometric functions (such as sine and cosine), may also be used, in certain cases. For example, trajectories of objects under the influence of gravity follow a parabolic path, when air resistance is ignored. Hence, matching trajectory data points to a parabolic curve would make sense. Tides follow sinusoidal patterns, hence tidal data points should be matched to a sine wave, or the sum of two sine waves of different periods, if the effects of the Moon and Sun are both considered.


title: Curve fitting

text: For a parametric curve, it is effective to fit each of its coordinates as a separate function of arc length; assuming that data points can be ordered, the chord distance may be used.


title: Curve fitting

text: Coope approaches the problem of trying to find the best visual fit of circle to a set of 2D data points. The method elegantly transforms the ordinarily non-linear problem into a linear problem that can be solved without using iterative numerical methods, and is hence much faster than previous techniques.


title: Curve fitting

text: The above technique is extended to general ellipses by adding a non-linear step, resulting in a method that is fast, yet finds visually pleasing ellipses of arbitrary orientation and displacement.


title: Curve fitting

text: Note that while this discussion was in terms of 2D curves, much of this logic also extends to 3D surfaces, each patch of which is defined by a net of curves in two parametric directions, typically called u and v. A surface may be composed of one or more surface patches in each direction.


title: Curve fitting

text: Many statistical packages such as R and numerical software such as the gnuplot, GNU Scientific Library, MLAB, Maple, MATLAB, TK Solver 6.0, Scilab, Mathematica, GNU Octave, and SciPy include commands for doing curve fitting in a variety of scenarios. There are also programs specifically written to do curve fitting; they can be found in the lists of statistical and numerical-analysis programs as well as in .


title: 1985 in film

text: The following is an overview of events in 1985 in film, including the highest-grossing films, award ceremonies and festivals, a list of films released and notable births and deaths.


title: 1985 in film

text: The year was considered an unsuccessful one for film. Despite a record number of film releases, many films failed at the box office, and ticket sales were down 17% compared with 1984. Industry executives believed the problem, in part, was a lack of original concepts. Films about fantasy and magic failed, as audiences leaned towards science-fiction. Janet Maslin said the fault for this lay partly with Steven Spielberg, who had created such a successful template with films like "E.T. the Extra-Terrestrial" and "Close Encounters of the Third Kind" that many fantasy films had imitated them. There was also a saturation of youth-oriented films targeted at those under 18. Executives were not fond of these films, but the financial rewards were too significant to ignore. The few films aimed at older audiences, like "Cocoon", were surprise successes. Only "Back to the Future" and "Rambo: First Blood Part II" were successful blockbusters, earning more than double the box office of "Cocoon". Films offering escapism and pro-America themes like "Rambo: First Blood Part II" and "Rocky IV" had also fared well.


title: 1985 in film

text: The glut of youth-targeted films like "Return to Oz" and "The Black Cauldron", and science-fiction comedies like "Weird Science", "Real Genius", and "My Science Project" had resulted in a string of failures. Executives said that the films were all very similar and marketed in the same way, offering no variety for audiences.


title: Cover version

text: In popular music, a cover version, cover song, remake, revival, or simply cover, is a new performance or recording by a musician other than the original performer or composer of the song. Originally, it referred to a version of a song released around the same time as the original in order to compete with it. Now, it refers to any subsequent version performed after the original.


title: Cover version

text: The term "cover" goes back decades when cover version originally described a rival version of a tune recorded to compete with the recently released (original) version. Examples of records covered include Paul Williams' 1949 hit tune "The Hucklebuck" and Hank Williams' 1952 song "Jambalaya". Both crossed over to the popular hit parade and had numerous hit versions. Before the mid-20th century, the notion of an original version of a popular tune would have seemed slightly odd – the production of musical entertainment was seen as a live event, even if it was reproduced at home via a copy of the sheet music, learned by heart or captured on a gramophone record. In fact, one of the principal objects of publishing sheet music was to have a composition performed by as many artists as possible. This made the song more important than the performing artist and rival cover or 'copycat' versions would vie for success.


title: Cover version

text: In previous generations, some artists made very successful careers of presenting revivals or reworkings of once-popular tunes, even out of doing contemporary "cover versions" of current hits. Since the 1950s, musicians now play what they call "cover versions" (the reworking, updating, or interpretation) of songs as a tribute to the original performer or group. Using familiar material (such as evergreen hits, standard tunes or classic recordings) is an important method of learning music styles. Until the mid-1960s most albums, or long playing records, contained a large number of evergreens or standards to present a fuller range of the artist's abilities and style. (See, for example, "Please Please Me".) Artists might also perform interpretations ("covers") of a favorite artist's hit tunes for the simple pleasure of playing a familiar song or collection of tunes.


title: Cover version

text: Tribute acts or bands are performers who make a living by recreating the music of one particular artist or band. Bands such as Björn Again, Led Zepagain, The Fab Four, Australian Pink Floyd Show and the Iron Maidens are dedicated to playing the music of ABBA, Led Zeppelin, The Beatles, Pink Floyd, and Iron Maiden respectively. Some tribute acts salute the Who, The Rolling Stones and many other classic rock acts. Many tribute acts target artists who remain popular but no longer perform, allowing an audience to experience the "next best thing" to the original act. The formation of tribute acts is roughly proportional to the enduring popularity of the original act; for example, dozens of Beatles tribute bands have formed and an entire subindustry has formed around Elvis impersonation. Many tribute bands attempt to recreate another band's music as faithfully as possible, but some such bands introduce a twist. Dread Zeppelin performs reggae versions of the Zeppelin catalog and Beatallica creates heavy metal fusions of songs by the Beatles and Metallica. There are also situations in which a member of a tribute band will go on to greater success, sometimes with the original act they tribute. One notable example is Tim "Ripper" Owens who, once the lead singer of Judas Priest tribute band British Steel, went on to join Judas Priest himself.


title: Cover version

text: Cover acts or bands are entertainers who perform a broad variety of crowd-pleasing cover songs for audiences who enjoy the familiarity of hit songs. Such bands draw from either current Top 40 hits or those of previous decades to provide nostalgic entertainment in bars, on cruise ships and at such events as weddings, family celebrations and corporate functions. Since the advent of inexpensive computers, some cover bands use a computerized catalog of songs, so that the singer can have the lyrics to a song displayed on a computer screen. The use of a screen for lyrics as a memory aid can dramatically increase the number of songs a singer can perform.


title: Cover version

text: Revivalist artists or bands are performers who are inspired by an entire genre of music and dedicate themselves to curating and recreating the genre and introducing it to younger audiences who have not experienced that music first hand. Unlike tribute bands and cover bands who rely primarily on audiences seeking a nostalgic experience, revivalist bands usually seek new young audiences for whom the music is fresh and has no nostalgic value. For example, Sha Na Na started in 1969 as a celebration of the doo-wop music of the 1950s, a genre of music that was not initially fashionable during the hippie counter-culture era. The Blues Brothers started in 1978 as a living salute to the blues, soul and R&B music of the 1950s and 1960s that was not in vogue by the late 1970s. The Blues Brothers' creed was that they were "on a mission from God" as evangelists for blues and soul music. The Black Crowes formed in 1984, initially dedicated to reviving 1970s style blues-rock. They started writing their own material in the same vein.


title: Cover version

text: Since the Copyright Act of 1909, United States musicians have had the right to record a version of someone else's previously recorded and released tune, whether it is music alone or music with lyrics. A license can be negotiated between representatives of the interpreting artist and the copyright holder, or recording published tunes can fall under a mechanical license whereby the recording artist pays a standard royalty to the original author/copyright holder through an organization such as the Harry Fox Agency, and is safe under copyright law even if they do not have any permission from the original author. A similar service was provided by Limelight by RightsFlow, until January 2015, when they announced they will be closing their service. The U.S. Congress introduced the mechanical license to head off an attempt by the Aeolian Company to monopolize the piano roll market.


title: Cover version

text: Although a composer cannot deny anyone a mechanical license for a new recorded version, the composer has the right to decide who will release the first recording of a song. Bob Dylan took advantage of this right when he refused his own record company the right to release a live recording of "Mr. Tambourine Man". Even with this, pre-release cover versions of songs can occasionally occur.


title: Cover version

text: Live performances of copyrighted songs are typically arranged through performing rights organizations such as ASCAP or BMI.


title: Cover version

text: Early in the 20th century it became common for phonograph record labels record companies to have singers or musicians "cover" a commercially successful "hit" tune by recording a version for their own label in hopes of cashing in on the tune's success. For example, "Ain't She Sweet" was popularized in 1927 by Eddie Cantor (on stage) and by Ben Bernie and Gene Austin (on record), was repopularized through popular recordings by Mr. Goon Bones & Mr. Ford and Pearl Bailey in 1949, and later still revived as 33 and 45 RPM records by the Beatles in 1964.


title: Cover version

text: Because little promotion or advertising was done in the early days of record production, other than at the local music hall or music store, the average buyer purchasing a new record usually asked for the tune, not the artist. Record distribution was highly localized, so a locally popular artist could quickly record a version of a hit song from another area and reach an audience before the version by the artist(s) who first introduced the tune in a particular format—the "original", "introductory" or "popularizing" artist—was widely available, and highly competitive record companies were quick to take advantage of these facts.