Compact disk

Compact disk

the Compact disk (short: CD, English for compact disk) is an optical mass storage, at the beginning of the 80's for digital storage by music of Philips and Sony was introduced (audio CD) and those Record to replace should.

Later the format of the Compact disk was extended, in order not to be able to store only music. As CD-ROM it is used since then also for storage of data for computers.

Table of contents

history

in the 70's experimented technicians of all electronics companies with digitalRecording of sound. The first prototypes were based on magnetic storage media, as for instance the classical audio cartridge. The first coming on the market in the year 1977 was an extension of the beta max - video recorder of the company Sony over an analog-digital and/or. Digital-analog converter (PCM- Modulator and/or. - Demodulator). By the video recorder instead of a video signal the PCM signal is noted, which - by appropriate coding in „lines “and/or. „Pictures “(Frames) organizes - from the view of a video recorder like a video signal looks. The klobige equipment and thoseInterferences with the admission could not convince the consumers. Sony developed special procedures, in order to eliminate the interferences. In order to test these procedures, secretly with a sample of a concert by harsh ore by Karajan in September 1978 photographs were taken. Karajanby Sony one invited later to judge the photographs.

Light reflection of the Compact disk

simultaneous one worked at the company Philips on the optical recording of picture signals, which the video technology should revolutionize. Soon the idea, this technology developedto use also for digital sounds. Both companies stood suddenly before an enormous problem. They had planned the new optical data media (laser disk), similarly the record, with a diameter of 30 cm. During the recording of moved pictures could it on it about 30 minutes video material accommodate. With audio data however the capacity was enough for 13 hours and 20 minutes. Sony was clear that the business model of the music industry would break down, if they marked such quantities out of music to the consumers should.

After the Compact cartridge (audio cartridge) was alone developed 1963 by the company Philips, both companies tried to cause a common standard here. In its article The Compact disk story [1] describes Philips engineer Kees Immink, which considerations and decisions to thatin the so-called “talk Book” - standard fixed technical parameters that CD led. In particular for the Spieldauer crucial diameters that CD by the Philips guidance one argued as follows: The Compact cartridge was a large success, the CD should be not much larger.The Compact cartridge had a diagonal of 11.5cm, engineers made the CD 0.5cm larger. All kinds of modern legends climb around the definition of these parameters, which are unfortunately not more applicable more excitingly however than true history; one thatmost beautiful and most popular is the following: After some differences Sony suggested that at least Ludwig van Beethovens ninth symphony in full length the new CD should seize. This suggestion was connected with of Sony vice-president at that time, Norio Ohga, some trained opera singerwas and itself always wished to be able to hear Beethovens ninth without disturbing changing of the clay/tone carrier. Ohgas favourite version, directed of harsh ore of Karajan, took 66 minutes, the technicians adhered to the then longest the available version ofWilliam Furtwängler. The admission from the year 1951 took accurately 74 minutes. 74 minutes meant 12 cm diameters of the optical data medium. The developers of Philips reacted with skepticism, since a so large disk would not fit into the suit bags.Thereupon Sony developers suit from all world, with the result will extent that for 12 cm everywhere place is. Thus Beethoven had specified a new standard.1980 about both companies for audio photographs “talk Book” - standard specified. With the diameter of theInterior hole that the Dutchmen succeeded CD (15 mm). As yardstick for this at that time world-wide smallest coin, the Netherlands piece of 10-cent (the “Dubbeltje in such a way specified” served).

On the radio exhibition 1981 in Berlin the CD for the first time publicly one introduces. In the yearwhereupon, to 17. August 1982, began those in Langenhagen with Hanover, in the manufacturing plants of the Polygram at that time, world-wide first industrielle production, before at the 1. October 1982 first in series produced CD players on thatMarket to be offered could.1988 was produced world-wide already 100 million audio CDs.

function mode

structure CD

Querschnitt durch eine CD
cross section by CD

the CD consists mostly of a transparent substrate (polycarbonate), thatby means of spraying coining/shaping one forms. The top side of this carrier contains the digital information in the form of micrometer-small recesses (pit), which are not even to be recognized by an optical microscope (separate for example only by a raster probe microscope), and gaps („country “), tooa only one long, spiral trace are arranged (altogether about 5 km).

This „informationshaltige “surface is vaporized with a thin aluminum film and finally protected with a paint coat and possibly provided or printed on with a label. These information becomes in the playing equipment ofa laser by the carrier layer scanned. From this it follows also that the laser sees pit not as recesses, but by polycarbonate as hill.

A trace section of approx. 0.278 micrometers length (a bit cell) places a so-called channel bit (zero or unity). A bit cell with a change at the beginning of country/pit or pit/country represents logical channel bit unity, a bit cell without such a change a logical channel bit zero (NRZ I coding).

Lesekopf eines CD-Laufwerks
Read head of a CD drive assembly

in such a way picked out data stream is EFM coded (English. Eight ton Fourteen modulation EFM), thatis called in each case 14 channel bits represent an 8-bit data item. The 14-Bit-Datenwörter is characterised by the fact that after each always at least two and maximally ten zeros follow unity. The 14-Bit-Datenwörter is - among other things for the Sicherstellung of this condition (some catch with unityon, others hear with unity on) - in each case still by three filling bits (also separation bits or Mergingbits called) from each other separated. With the selection the three filling bits are removed immediately from the data stream, and for ever 14 the EFM coded channel bits becomes thenby means of a translation table the appropriate value of the uncoded 8-bit data item determines.

The data are beyond that organized as blocks and Frames. Ever 24 uncoded bytes (according to 6 Stereo Samples) zzgl. 8 byte error correction information forms a Frame, from those again for 98 a blockform. A block contains thus 2352 byte uncoded utilizable data, of 75 blocks contains one second audio material. Altogether a data bit with approx. becomes. 3 channel bit codes.

Due to this structure of the data stream is surprisingly 200 per cent of more bits on the disk than genuineData bit: The shortest pit/country selectable of the point of laser is long for physical reasons scarcely a micrometer (833 Nm, limiting size is the diameter of the optimally focused point). The shortest pit/country (T3) codes three bits (100).

error correction and error covering

So that scratches do not affect data security negatively, the data are secured by means of parity bits, so that bit errors can be recognized and corrected. Further successive data bytes are distributed by Interleaving on a larger surface. The CROSS Interleave Reed Solomon code (CIRC) is by it in the situation to correct an error of up to 3500 bits (corresponds to a trace length of approximately 2.4 mm) and to compensate errors of up to 12000 bits (about 8.5 mm of trace length) with that audio CD. With very strongerScratching of the carrier of the lower surface is however the legibility reduced or completely impossible.

reading

Auslesevorgang bei einer CD
selection procedure with CD

scanning CD takes place by means of a laser diode. The ray of light becomes by means of a halfpermeable mirror in twoParts of same strength split up. One of the two partial jets is steered on the CD, reflected there and overlaid then with the other partial jet. The jet, which meets the CD, has to put a longer Laufstrecke back with a country than with one Pit. From interference of the light waves two different light intensities in the sum jet from the run time differences, which are seized with a photodiode and converted into electrical impulses, result.

The optics with the laser induces itself when playing first to the last TRACKcontrary to the record from the inside outward. In addition the CD do not have a firm angular speed; this is adapted to the momentary position of the read head, so that the path speed (CLV) and not, as with the record, the angular speed (CAV) is constant. If the read head of far outside on that CD reads, the CD thus more slowly one turns. Can everywhere on that CD with full recording density be worked and it is in this way ensured a constant data stream, howit with audio CDs is needed. In talk Book are fixed to two different speeds, 1.2 m/s and 1.4 m/s. Thus min. are according to play times of 74:41. and/or. 64:01 min., under maximum utilization of all tolerances 80:29 min, possible. This corresponds to a rotational speedof 500 min -1 at the beginning that CD (internal traces) to 200 min -1 at the outer edge that CD. The rotational speed is regulated by an automatic control loop on the basis the level of a FIFO buffer. Therefore no change-over (neither manually nor automatically) must depending uponlinear speed used take place. By the buffer mentioned fluctuations of the number of revolutions do not affect the rendition speed.

Many modern CD-ROM drive assemblies read data CDs however with constant angular speed, around time-consuming accelerating and deceleration that CD with and Herspringen of the read positionto avoid. Thus the data rate depends on the position of the read head with data CDs. The speed indicated on the packing is nearly always the maximum, not the average.

By the mechanical firmness that CD is the increase of the reading rate throughIncrease of the rotational speed borders set. So-called „52-fach “- drive assemblies turn the CD with up to 10000 min -1 at these speeds lead even smallest Unwuchten that CD to strong vibrations, which are clearly audible on the one hand and on the other hand in the long term both drive assemblyand medium to damage know.

variants

This article or section requires a revision. Details are indicated on the discussion side. Please to improve it and removes afterwards this marking helps.

The specifications of the CD-ROM are in „Yellow Book “- standard fixed. A platform-spreading file system of the CD-ROM was fixed by the ISO in the standard ISO 9660. Its successor reads UDF.

To that, Book admits the format specifications of audio CD (short CD-DA) “as „talks - standard, became from the NetherlandsElectronics company Philips sketched. Philips possesses also the right of the Lizenzierung „of the Compact disk digital audio “- Logos. The music information is stored in 16-Bit Stereo and a scanning rate by 44.1 kHz.

Mini CD
CDs gives it in two different sizes, furthest is commonthe version with a diameter of 120 mm and 15 gram weight, more rarely the mini CD with a diameter of 80 mm and 30% of the storage capacity. Besides there are also CDs, which have another form than a round disk.These free formings in such a way specified (Shape CDs) are not however popular due to playing problems (possible imbalance, no introduction into Slot drive assemblies).

Some CD players are able, HDCD so mentioned - CDs to play. This CDs is coded with genuine 20 bits music information(instead of with 16) and are to sound better with high-quality music plants. HDCD CDs are completely compatible with „normal “CD players.

CD video is a combination of CD-DA (audio CD) and LV/LD (videodisc) with digital only audio part and similar video part.

There are different possibilities, audio CD contents andTo combine CD-ROM contents on a disk. The simplest possibility is to bring a data TRACK with CD-ROM contents as first TRACKs on the CD (Enhanced CD). The nowadays practically futile advantage that the CD-ROM part also in exclusively single-sessionable CD-ROM drive assembliesto be read, opposes the comparatively large disadvantage of the visibility of this data TRACK for normal audio CD players can - in particular, since some older CD players make possible also a rendition of the CD-ROM data than audio data. That expresses itself depending upon volume attitude in deafening and loudspeaker loudspeaker-mutilate-mutilating thatNoise.

As advancement the data TRACK was provided with an index position of 0, whereby this is not started so easily by the CD player (i-Trax). The audio material begins, as with simple audio CDs, at index position 1 from TRACKs 1. (Problematic for thosePlaying compatibility could be the fact that within the TRACK the mode of CD-ROM mode 1 on audio changes.)

nowadays to become this purpose practically excluding Multisession CDs used - the audio data lay in the first session, while the CD-ROM data ina second session are contained, which is not read by audio CD players (CD extra, CD plus). Naturally for the CD-ROM part a multi-sessionable CD-ROM drive assembly is needed.

A combination is the CD+G (CD+Graphics). Places these CD at the same time to the music graphic data, howfor example the song text, on a screen. Most frequent application of this format is Karaoke. In a normal CD player the CD+G is playable as normal audio CD. On special devices (in recent time also on some DVD Playern) is to the music alsothe diagram on the screen visibly. The additional data are stored in the Subcode that CD, D. h. they are visible contrary to contents of data TRACKs not so easily for an operating system.

Clearly more frequently to find against it CDs with CD text are . In the Subcode that CD (usually in Lead in) are stored additional information, like titles and artists. These information is then indicated to that by appropriate Playern during playing CD.

Advancements that CD are the DVD - audio and those Super audio Compact disk. DVD media offer substantially larger capacities of 4,7 GB (single more layer) to 8.5 GB (doubles/binary more layer). The main advantage is not thereby a longer play time, but that the audio data in 5.1-Sound are present. While the super audio CD and DVD audio exclusivefor audio data to be used, different data types are possible with the DVD (DVD DATA, DVD video, DVD audio, DVD Rome, DVD+/-R (W)). However the DVD within the audio range did not become generally accepted yet.

One of Sony developed further variant that CD was those Double Density Compact disk (DDCD). The capacity of 650 MT is doubled thereby. It was available in 2 variants, a recordable (DDCD-R) and a again-recordable (DDCD-RW).

There is also CD-i, CDTV, photo CD, video CD.

Copy protection

since 2001 in Germany also silver disks are sold, which contain „a copy protection in such a way specified “, which is to prevent the digital selection of the audio data (and thus copying the data). They are likewise called CD, to correspondbut the regulations do not talk Book and are therefore no genuine audio CDs. This CDs is called therefore also „Un-CDs “(Unknown CD). Some CD playing devices give Unknown to CD (and/or. Un-CD) as error message in the display out, if oneinserted CD one does not recognize.

The copy protection is realized, as errors or a second incorrect session are brought in. Also deviations about talk Book - standard are possible however rather rare. It is thereby „a playing protection “, since the errors are to cause thatthe disks no more in the CD drive assembly of a PC to play do not leave themselves. This is to prevent so a copying. Some CD drive assemblies cannot be impressed and known of it however the data nevertheless read, whereby the idea „of the copy protection becomes useless “.

Insteadcause the errors on „the copy-protected “CD problems on numerous normal audio CD players and many car radios with integrated CD unit. These can partly play these media either not at all or only, partly develop even serious hardware defects, about if the firmware of the CD playerand the medium falls any longer to eject does not leave themselves. In addition the clay/tone quality and the life span of the playing equipment under the copy protection often suffers.

Starting from that 1. The manufacturers are legally committed to November 2003 to mark copy-protected media as such. Such markingsis however hardly to be taken, which problems can occur in individual cases with car radios, MP3-CD-Spielern, DVD players and other devices.

Since the copy protection is hardly effective in practice and leads again and again on the other hand to problems when playing, have in the meantime (2005) some labels the concept “copy-protected CD” again given up and publish again usual, unprotected talk Book CDs, particularly since so in addition royalties for the copy protection can be saved.

recordable CDs

data layer of a blank

recordable CDs gives it in one oncerecordable variant (CD-R: CD recordable) and in a several times again-recordable variant (CD-RW: CD rewritable). While the reflection characteristics of a CD-R those normal CD almost resembled and this should to be able to be read thus even in older CD drive assemblies,the read head output signal of a CD-RW is by far weaker, so that these media only of according to equipped (newer) drive assemblies and/or. Players to be read can.

For describing CD cannot be used a usual CD player. For this is a CD burner so mentioned (and/or. CD-Rekorder) necessarily. CD burners can not only describe but also read CDs. Therefore pure CD-ROM readers for computers disappear since the year 1999 slowly from the market.

The ISO-9660 - File format of a CD-ROM does not permit subsequent changes. In addition recordable CDs can - inContrast to non removable disks - to be not block-by-block described. Therefore only „an image in such a way specified must be put on “, which contains an accurate copy on the CD to burning data. This image can then (as a TRACK) in a passage upthe CD „“become burned. But special CD fuel programs are necessary. Current fuel programs control a providing of the image „on-the-fly “, i.e., the ISO image is produced during the letter.

However it is possible, additional with a further recording procedure in a further TRACK (thatnormally that is called CD a new file system to produce in a further session). The listings of this new file system can referenzieren also to files in the older TRACKs. Since with the normal enterprise the file system of the last TRACK is always used,it is possible to add files to rename too „deletes “and too „overwrites “. Naturally the reserved seat cannot again be used. With special software (within the Windows range for example „Isobuster “) can be accessed also the older file systems, i.e., „the deleted “Files and/or. the older versions „more overwritten “files are there still present (Multisession CD).

Alternatively the file systems in the TRACKs can be regarded CD (similar to partitions of a non removable disk) as different virtual drive assemblies (Multivolume CD). This procedure e.g. became. with the MacOS inthe versions 8.x to 9.x assigned, is however otherwise hardly common.

CD-RWs can be described theoretically block-by-block. That must be supported also by the CD burner. Since the ISO-9660-Dateiformat used on CD-ROM does not support subsequent changes at files, for this a its own became File system named UDF imported, which is used on DVDs. This format permits it to be stored as for example with a disk, directly files on that CD.

label print

for the label print with that CD, likewiseas is the case for the DVD, different printings to the selection:

Screen printing: In the screen printing decoration colors (HKS or Pantone) are possible be selected up to 6 label colors, it can. Screen printing is at present the current version, in order to print CDs or DVDs on,however more and more is displaced by the offset printing. The screen printing is suitably for pressed CDs and DVDs, also the blank printing in the screen printing is possible. In the screen printing the colors are very brilliant.

Trockenoffsetdruck: In the drying offset 4 label colors are possible (CMYK), combines with the screen printing up to 6 label colors (CMYK in the offset and additionally full surface and a decoration color in the screen printing knows). Due to higher resolution than in the screen printing the offset printing is ideal for photo-realistic representations. Since beginning2004 are possible the offset printing not only for pressed CDs and DVDs, but also for CD blanks and DVD blanks.

Thermal transfer printing: With this compression matter color of a ribbon becomes by heating the print head up on the CD or with a special printerDVD transfer. Technically conditionally the compression matter is rather suitable for writings and Logos. In practice this procedure is used with small editions (CDs and DVDs even burned).

Thermal RH transfer printing: The Thermoretransferdruck is the advancement of the thermal transfer printing. ThatMotive for label is printed in the thermal transfer printing procedure on a transmission volume and of it a foil on the CD is then applied. By this technology a better dissolution is possible. So a photo-realistic pressure can be already achieved with Kleinauflagen.

Lightscribe - procedures: With this procedurethe laser of an Lightscribe able CD burner burns any gray tone diagram, which will transfer by means of appropriate software sketched and to the burner on the front of appropriate blanks. The combustion lasts momentarily (March 2005) in substantial quality still quite long (over 30 minutes).Also color will shortly be possible.

environmental protection

the Compact disk consists mainly of the valuable plastic polycarbonate. A sort-pure recycling is not worthwhile itself for the production of new Compact disks, however the very high-quality raw material can inthe medicine, which PC and the automobile industry are used. In Germany there was the collecting system CD-Collect, which CD recycling had as business model. The company stopped its business concern however.

CDs with sensitive data, which are not no more needed, leave themselves approximatelyunauthorized reading protect, as the layer of metal (and thus the data layer) with pointed article is zerkratzt. No more cannot such CD be read with normal CD drive assemblies. A selection of the zerkratzten ranges that CD is with special readers stillpossible, but very aufwändig and expensively and exceeds usually the value of the data. For extremely sensitive data exists special CD Shredder, which CDs and other optical data media into so small pieces häckseln, so that as reliable destroys the data mediato apply can, whereby the recycling ability of the data medium remains ensured.

literature

  • Hartmut Gieselmann: Against forgetting. US researchers examine life span of [recordable] CDs and DVDs. In: c't, 1/2005. Heise publishing house, S. 44
  • Kees Immink, The Compact disk story, Journal OF the audio engineering Society, 46 (5), pp. 458-465, May 1998 [2].


see also

of formats

Web on the left of

Wiktionary: CD - Word origin, synonyms and translations
Commons: Compact disk - pictures, videos and/or audio files
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