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CD-ROM
From Wikipedia, the free encyclopedia

CD-ROM
Media type Optical disc

Capacity

194 MiB (8 cm) 650–900 MB (12 cm)

Read mechanism

150 KiB/s (1×) 10,800 KiB/s (72×)

Write mechanism

150 KiB/s (1×) 8,400 KiB/s (56×)

Standard

ISO/IEC 10149[1]

Usage

Data storage, video, audio, open internet

Optical discs

    

Optical disc Optical disc drive Optical disc authoring Authoring software Recording technologies

 

Recording modes Packet writing Optical media types

 

Blu-ray Disc (BD): BD-R, BD-RE DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-R

DS, DVD+R DS, DVD-RW,DVD+RW, DVD-RAM, DVDD, HVD, EcoDisc



Compact Disc (CD): Red Book, CD-ROM,CD-R, CD-RW, 5.1 Music Disc, SACD,PhotoCD, CD Video (CDV), Video CD (VCD),SVCD, CD+G, CD-Text, CD-ROM XA, CD-i

               

Universal Media Disc (UMD) Enhanced Versatile Disc (EVD) Forward Versatile Disc (FVD) Holographic Versatile Disc (HVD) China Blue High-definition Disc (CBHD) HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM High definition Versatile Multilayer Disc (HD VMD) VCDHD GD-ROM MiniDisc (MD) (Hi-MD) Laserdisc (LD) Video Single Disc (VSD) Ultra Density Optical (UDO) Stacked Volumetric Optical Disk (SVOD) Five dimensional discs (5D DVD) Nintendo optical disc (NOD) Standards




Rainbow Books File systems



ISO 9660

  

Joliet Rock Ridge / SUSP El Torito

 

Apple ISO 9660 Extensions

Universal Disk Format (UDF)



Mount Rainier See also

 

History of optical storage media High definition optical disc format war
This box: view · talk · edit

CD-ROM (pronounced /ˌsiːˌdiːˈrɒm/, an acronym of "compact disc read-only medium") is a prepressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data.[2] CD-ROMs are popularly used to distribute computer software, including games and multimedia applications, though any data can be stored (up to the capacity limit of a disc). Some CDs hold both computer data and audio with the latter capable of being played on a CD player, while data (such as software or digital video) is only usable on a computer (such as ISO 9660 format PC CD-ROMs). These are called enhanced CDs. Although many people use lowercase letters in this acronym, proper presentation is in all capital letters with a hyphen between CD and ROM. At the time of the technology's introduction it had more capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding CDs, DVDs and Blu-ray, though some experimental descendants of it such as HVDs may have more space and faster data rates than today's biggest hard drive.
Contents
[hide]



1 Media

○ ○

1.1 Standard 1.2 CD-ROM format



1.2.1 CD sector contents

○ ○ •

1.3 Manufacture 1.4 Capacity

2 CD-ROM drives

○ ○ • • •

2.1 Laser and optics 2.2 Transfer rates

3 Copyright issues 4 See also 5 References

[edit]Media
Main article: Compact Disc CD-ROM discs are identical in appearance to audio CDs, and data are stored and retrieved in a very similar manner (only differing from audio CDs in the standards used to store the data). Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminium to make a reflective surface. The most common size of CD-ROM disc is 120 mm in diameter, though the smaller Mini CD standard with an 80 mm diameter, as well as numerous non-standard sizes and shapes (e.g., business card-sized media) are also available. Data is stored on the disc as a series of microscopic indentations. A laser is shone onto the reflective surface of the disc to read the pattern of pits and lands ("pits", with the gaps between them referred to as "lands"). Because the depth of the pits is approximately one-quarter to one-sixth of the wavelength of the laser light used to read the disc, the reflectedbeam's phase is shifted in relation to the incoming beam, causing destructive interference and reducing the reflected beam's intensity. This pattern of changing intensity of the reflected beam is converted into binary data.

[edit]Standard
Several formats are used for data stored on compact discs, known as the Rainbow Books. These include the original Red Book standards for CD audio,White Book and Yellow Book CD-ROM. The ISO/IEC 10149 / ECMA-130 standard, which gives a thorough description of the physics and physical layer of the CD-ROM, inclusive of cross-interleaved Reed-Solomon coding (CIRC) and eight-to-fourteen modulation (EFM), can be downloaded from ISO[1] or ECMA.[3] ISO 9660 defines the standard file system of a CD-ROM, although it is due to be replaced by ISO 13490 (which also supports CD-R and multi-session).UDF extends ISO 13346 (which was designed for non-sequential writeonce and re-writeable discs such as CD-R and CD-RW) to support read-only and re-writeable media and was first adopted for DVD. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito. CD-ROM drives are rated with a speed factor relative to music CDs (1× or 1-speed which gives a data transfer rate of 150 KiB/s). 12× drives were common beginning in early 1997. Above 12× speed, there are problems

with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 30× at the outer edge of the disc with the same rotational speed as a standard constant linear velocity (CLV) 12×, or 32× with a slight increase. However due to the nature of CAV (linear speed at the inner edge is still only 12×, increasing smoothly in-between) the actual throughput increase is less than 30/12 – in fact, roughly 20× average for a completely full disc, and even less for a partially filled one. Problems with vibration, owing to e.g. limits on achievable symmetry and strength in mass produced media, mean that CDROM drive speeds have not massively increased since the late 90s. Over 10 years later, commonly available drives vary between 24× (slimline and portable units, 10× spin speed) and 52× (typically CD- and read-only units, 21× spin speed), all using CAV to achieve their claimed "max" speeds, with 32× through 48× most common. Even so, these speeds can cause poor reading (drive error correction having become very sophisticated in response) and even shattering of poorly made or physically damaged media, with small cracks rapidly growing into catastrophic breakages when centripetally stressed at 10,000 – 13,000rpm (i.e. 40–52× CAV). High rotational speeds also produce undesirable noise from disc vibration, rushing air and the spindle motor itself. Thankfully, most 21st century drives allow forced low speed modes (by use of small utility programs) for the sake of safety, accurate reading or silence, and will automatically fall back if a large number of sequential read errors and retries are encountered. Other methods of improving read speed were trialled such as using multiple pickup heads, increasing throughput up to 72× with a 10× spin speed, but along with other technologies like 90~99 minute recordable media and "double density" recorders, their utility was nullified by the introduction of consumer DVDROM drives capable of consistent 36× CDROM speeds (4× DVD) or higher. Additionally, with a 700mb CDROM fully readable in under 2½ minutes at 52× CAV, increases in actual data transfer rate are decreasingly influential on overall effective drive speed when taken into consideration with other factors such as loading/unloading, media recognition, spin up/down and random seek times, making for much decreased returns on development investment. A similar stratification effect has since been seen in DVD development where maximum speed has stabilised at 16× CAV (with exceptional cases between 18× and 22×) and capacity at 4.3 and 8.5GiB (single and dual layer), with higher speed and capacity needs instead being catered to by Blu-Ray drives.

[edit]CD-ROM

format

A CD-ROM sector contains 2,352 bytes, divided into 98 24-byte frames. Unlike a music CD, a CD-ROM cannot rely on error concealment by interpolation, and therefore requires a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed–Solomon error correction.[4] A Mode-1 CD-ROM, which has the full three layers of error correction data, contains a net 2,048 bytes of the available 2,352 per sector. In a Mode-2 CD-ROM, which is mostly used for video files, there are 2,336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM, based on comparison to CDDA audio standards, is 44100 Hz × 16 bits/sample × 2 channels × 2,048 / 2,352 /8 = 153.6 kB/s = 150 KiB/s. The

playing time is 74 minutes, or 4,440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682 MB or, equivalently, 650 MiB. A 1× speed CD drive reads 75 consecutive sectors per second.

[edit]CD sector contents




A standard 74 min. CD contains 333,000 blocks or sectors. Each sector is 2,352 bytes, and contains 2,048 bytes of PC (mode 1) data, 2,336 bytes of PSX/VCD (mode 2) data, or 2,352 bytes of audio.



The difference between sector size and data content are the header information and the error-correcting codes, that are big for data (high precision required), small for VCD (standard for video) and none for audio.



If extracting the disc in raw format (standard for creating images) always extract 2,352 bytes per sector, not 2,048/2,336/2,352 bytes depending on data type (basically, extracting the whole sector). This fact has two main consequences:



Recording data CDs at very high speed (40×) can be done without losing information. However, as audio CDs do not contain a third layer of error-correcting codes, recording these at high speed may result in more unrecoverable errors or 'clicks' in the audio.



On a 74 minute CD, one can fit larger images using raw mode, up to 333,000 × 2,352 = 783,216,000 bytes (~747 MiB). This is the upper limit for raw images created on a 74 min or ~650 MiBRed Book CD. The 14.8% increase is due to the discarding of error correction data

 

The sync pattern for Mode 1 CDs is 0xff00ffffffffffffffff00ff[3]

An image size is always a multiple of 2,352 bytes (the size of a block) when extracting in raw mode.[5]

Layout type

← 2,352 byte block →

CD digital audio:

2,352 Digital audio

CDROM 12 4 (mode Sync. Sector id. 1):

2,048 Data

4 8 Error detectio Zero n

276 Error correction

CD-

12

4

2,336

ROM (mode Sync. Sector id. 2):

Data

[edit]Manufacture
Main article: Compact Disc manufacturing Pre-pressed CD-ROMs are mass-produced by a process of stamping where a glass master disc is created and used to make "stampers", which are in turn used to manufacture multiple copies of the final disc with the pits already present. Recordable (CD-R) and rewritable (CD-RW) discs are manufactured by a different method, whereby the data are recorded on them by a laser changing the properties of a dye or phase transition material in a process that is often referred to as "burning".

[edit]Capacity

A CD-ROM can easily store the entirety of an English encyclopedia's words and images, plus audio & video clips

CD-ROM capacities are normally expressed with binary prefixes, subtracting the space used for error correction data. A standard 120 mm, 700 MB CD-ROM can actually hold about 737 MB (703 MiB) of data with error correction (or 847 MB total). In comparison, a single-layer DVD-ROM can hold 4.7 GB of error-protected data, more than 6 CD-ROMs.

Capacities of Compact Disc types (90 and 99 minute discs are not standard)

(MB)

Approx. (MiB)

(MB)

(min)

8 cm

94,500

193.536

184.570

222.264

21

283,500

580.608

553.711

666.792

63

650 MB

333,000

681.984

650.391

783.216

74

700 MB

360,000

737.280

703.125

846.720

80

800 MB

405,000

829.440

791.016

952.560

90

900 MB

445,500

912.384

870.117

1,047.816

99

Note: megabyte (MB) and minute (min) values are exact; MiB values are approximate.

[edit]CD-ROM

drives

Further information: Optical disc drive CD-ROM discs are read using CD-ROM drives. A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI, S-ATA, Firewire, or USB interface or a proprietary interface, such as thePanasonic CD interface. Virtually all modern CD-ROM drives can also play audio CDs as well as Video CDs and other data standards when used in conjunction with the right software. CD-ROM drive can sometimes be a misnomer for newer drives that are capable for reading and burning DVDs, the CD's successor which is now the standard optical disc drive.

[edit]Laser

and optics

CD-ROM drives employ a near-infrared 780 nm laser diode. The laser beam is directed onto the disc via an opto-electronic tracking module, which then detects whether the beam has been reflected or scattered.

[edit]Transfer

rates

If a CD-ROM is read at the same rotational speed as an audio CD, the data transfer rate is 150 KiB/s, commonly referred to as "1×". At this data rate, the track moves along under the laser spot at about 1.2 m/s. To maintain this linear velocity as the optical head moves to different positions, the angular velocity is varied from 500 rpm at the inner edge to 200 rpm at the outer edge. By increasing the speed at which the disc is spun, data can be transferred at greater rates. For example, a CD-ROM drive that can read at 8× speed spins the disc at 1600 to 4000 rpm, giving a linear velocity of 9.6 m/s and a transfer rate of 1200 KiB/s. Above 12× speed most drives read at Constant angular velocity (CAV, constant rpm) so that the motor is not made to change from one speed to another as the head seeks from place to place on the disc. In CAV mode the "×" number denotes the

transfer rate at the outer edge of the disc, where it is a maximum. 20× was thought to be the maximum speed due to mechanical constraints until Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate commonly available is about 52× or 10,400 rpm and 7.62 MiB/s. Higher spin speeds are limited by the strength of the polycarbonate plastic of which the discs are made. At 52×, the linear velocity of the outermost part of the disk is around 65 m/s. However, improvements can still be obtained by the use of multiple laser pickups as demonstrated by theKenwood TrueX 72× which uses seven laser beams and a rotation speed of approximately 10×. CD-Recordable drives are often sold with three different speed ratings, one speed for write-once operations, one for re-write operations, and one for read-only operations. The speeds are typically listed in that order; i.e. a 12×/10×/32× CD drive can, CPU and media permitting, write to CD-R discs at 12× speed (1.76 MiB/s), write to CD-RW discs at 10× speed (1.46 MiB/s), and read from CD discs at 32× speed (4.69 MiB/s). The 1× speed rating for CD-ROM (150 KiB/s) is different than the 1× speed rating for DVDs (1.32 MiB/s).

A view of a CD-ROM drive's disassembled laser system.

The movement of the laser enables reading at any position of the CD.

The laser system of a CD Drive.

Common data transfer speeds for CD-ROM drives

Transfer speed

KiB/s

Mbit/s

RPM



150

1.23

200–500



300

2.46

400-1,000



600

4.92

800–2,000



1,200

9.83

1,600–4,000

10×

1,500

12.3

2,000–5,000

12×

1,800

14.7

2,400–6,000

20×

1,200–3,000 up to 24.6 4,000 (CAV)

32×

1,920–4,800 up to 39.3 4,800 (CAV)

36×

2,160–5,400 up to 44.2 7,200 (CAV)

40×

2,400–6,000 up to 49.2 8,000 (CAV)

48×

2,880–7,200 up to 59.0 9,600 (CAV)

52×

3,120–7,800 up to 63.9 10,400 (CAV)

56×

3,360–8,400 up to 68.8 11,200 (CAV)

72×

6,750– 10,800

up to 88.5 2,000 (multi-beam)

[edit]Copyright

issues

Main article: CD/DVD copy protection There has been a move by the recording industry to make audio CDs (CDDAs, Red Book CDs) unplayable on computer CD-ROM drives, to prevent the copying of music. This is done by intentionally introducing errors onto the disc that the embedded circuits on most stand-alone audio players can automatically compensate for, but which may confuse CD-ROM drives. Consumer rights advocates are as of October 2001 pushing to require warning labels on compact discs that do not conform to the official Compact Disc Digital Audio standard (often called the Red Book) to inform consumers which discs do not permit full fair use of their content. In 2005, Sony BMG Music Entertainment was criticised when a copy protection mechanism known as Extended Copy Protection (XCP) used on some of their audio CDs automatically and surreptitiously installed copy-prevention software on computers (see 2005 Sony BMG CD copy protection scandal). Such discs are not legally allowed to be called CDs or Compact Discs because they break the Red Book standard governing CDs, and Amazon.com for example describes them as "copy protected discs" rather than "compact discs" or "CDs". Software distributors, and in particular distributors of computer games, often make use of various copy protection schemes to prevent software running from any media besides the original CD-ROMs. This differs somewhat from audio CD protection in that it is usually implemented in both the media and the software itself. The CD-ROM itself may contain "weak" sectors to make copying the disc more difficult, and additional data that may be difficult or impossible to copy to a CD-R or disc image, but which the software checks for each time it is run to ensure an original disc and not an unauthorized copy is present in the computer's CD-ROM drive. Manufacturers of CD writers (CD-R or CD-RW) are encouraged by the music industry to ensure that every drive they produce has a unique identifier, which will be encoded by the drive on every disc that it records: the

RID or Recorder Identification Code.[6] This is a counterpart to the SID—the Source Identification Code, an eight character code beginning with "IFPI" that is usually stamped on discs produced by CD recording plants.

DVD
From Wikipedia, the free encyclopedia

This article is about the storage media format. For the binocular vision condition, see Dissociated Vertical Deviation.

DVD

DVD-R read/write side

Media type

Optical disc

Capacity

4.7 GB (single-sided, single-layer – common) 8.5-8.7 GB (single-sided, double-layer) 9.4 GB (double-sided, single-layer) 17.08 GB (double-sided, double-layer – rare)

Read mechanism

650 nm laser, 10.5 Mbit/s (1×)

Write mechanism

10.5 Mbit/s (1×)

Standard

DVD Forum's DVD Books[1][2][3] and DVD+RW Alliance specifications

DVD, also known as Digital Video Disc or Digital Versatile Disc, is an optical disc storage media format, and was invented and developed by Philips,Sony, Toshiba, and Time Warner in 1995. Its main uses are video and data storage. DVDs are of the same dimensions as compact discs (CDs), but are capable of storing almost seven times as much data. Variations of the term DVD often indicate the way data is stored on the discs: DVD-ROM (read only memory) has data that can only be read and not written; DVD-R and DVD+R (recordable) can record data only once, and then function as a DVD-ROM; DVD-RW (re-writable), DVD+RW, and DVD-RAM(random access memory) can all record and erase data multiple times. The wavelength used by standard DVD lasers is 650 nm;[4] thus, the light has ared color. DVD-Video and DVD-Audio discs refer to properly formatted and structured video and audio content, respectively. Other types of DVDs, including those with video content, may be referred to as DVD Data discs.
Contents
[hide]

• • • • •

1 History 2 Specifications 3 Etymology 4 Identification (MID) 5 Design



5.1 As a movie delivery medium



5.2 As an interactive medium



6 Capacity

○ ○

6.1 Technology 6.2 Internal mechanism of a drive

• • •

7 DVD recordable and rewritable 8 Dual-layer recording 9 DVD-Video

○ ○ •

9.1 Security 9.2 Consumer rights

10 DVD-Audio

○ •

10.1 Security

11 Improvements and succession



11.1 HD DVD and Blu-ray Disc



11.2 Holographic Versatile Disc

○ • • • • •

11.3 5D DVD

12 Use as backup medium 13 See also 14 References 15 Further reading 16 External links

[edit]History
In 1993, two optical disc storage formats were being developed. One was the MultiMedia Compact Disc (MMCD) also called CDi, backed by Philips and Sony, and the other was the Super Density (SD) disc, supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. Representatives of the SD camp approached IBM, asking for advice on the file system to use for their disc as well as seeking support for their format for storing computer data. Alan E. Bell, a researcher from IBM's Almaden Research Center received that request and also learned of the MMCD development project. Wary of being caught in a repeat of the costly videotape format war betweenVHS and Betamax in the 1980s, he convened a group of computer industry experts, including representatives from Apple, Microsoft, Sun, Dell, and many others. This group was referred to as the Technical Working Group, or TWG.

The TWG voted to boycott both formats unless the two camps agreed on a single, converged standard.[5] Lou Gerstner, president of IBM, was recruited to apply pressure on the executives of the warring factions. Eventually, the computer companies won the day, and a single format, now called DVD, was agreed upon. The TWG also collaborated with the Optical Storage Technology Association(OSTA) on the use of their implementation of the ISO-13346 file system (known as Universal Disc Format [UDF] for use on the new DVDs. Philips and Sony decided it was in their best interest to avoid another format war over their MultiMedia Compact Disc, and agreed to unify with companies backing the Super Density Disc to release a single format with technologies from both. The specification was mostly similar to Toshiba and Matsushita's Super Density Disc, except for the dual-layer option (MMCD was single-sided and optionally dual-layer, whereas SD was single-layer but optionally double-sided) and EFMPlus modulation. EFMPlus was chosen because of its great resilience to disc damage, such as scratches and fingerprints. EFMPlus, created by Kees Immink (who also designed EFM), is 6% less efficient than the modulation technique originally used by Toshiba, which resulted in a capacity of 4.7 GB, as opposed to the original 5 GB. The result was the DVD specification, finalized for the DVD movie player and DVD-ROM computer applications in December 1995. The DVD Video format was first introduced by Toshiba in Japan in November 1996, in the United States in March 1997 (test marketed),[6] in Europe in October 1998, and in Australia in February 1999. In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.[6]

[edit]Specifications
DVD specifications created and updated by the DVD Forum are published as so-called DVD Books (e.g. DVDROM Book, DVD-Audio Book, DVD-Video Book, DVD-R Book, DVD-RW Book, DVD-RAM Book, DVDAR Book, DVD-VR Book, etc.).[1][2][3] Some specifications for mechanical, physical and optical characteristics of DVD optical discs can be downloaded as freely available standards from the ISO website.[7] Also, the DVD+RW Alliancepublishes competing DVD specifications such as DVD+R, DVD+R DL, DVD+RW or DVD+RW DL. These DVD formats are also ISO standards.[8][9][10][11] Some of DVD specifications (e.g. for DVD-Video) are not publicly available and can be obtained only from the DVD Format/Logo Licensing Corporation for a fee of US $5000.[12][13] Every subscriber must sign a nondisclosure agreement as certain information in the DVD Book is proprietary and confidential.[12]

[edit]Etymology
The official DVD specification documents have never defined the initialism DVD.[citation needed] Usage in the present day varies, with Digital Versatile Disc,[14] Digital Video Disc, and DVD being the most common.

DVD was originally used as an initialism for the unofficial term digital videodisk.[15] A newsgroup FAQ written by Jim Taylor (a prominent figure in the industry) claims that four years later, in 1999, the DVD Forum stated that the format name was simply the three letters "DVD" and did not stand for anything.
[16]

The DVD Forum website has a section called "DVD Primer" in which the answer to the question, "What does DVD mean?" reads, "The keyword is 'versatile.' Digital Versatile Discs provide superb video, audio and data storage and access—all on one disc."[17]

[edit]Identification

(MID)

The DVD is made of a spiral groove read or written starting at the center. The form of the groove encodes unalterable identification data known as Media Identification Code (MID). The MID contains data such as the manufacturer and model, byte capacity, allowed data rates (also known as speed), etc.

[edit]Design [edit]As

a movie delivery medium

DVD was adopted by movie and home entertainment distributors to replace the ubiquitous VHS tape as the primary means of distributing films to consumers in the home entertainment marketplace. DVD was chosen for its superior ability to reproduce moving pictures and sound, for its superior durability, and for its interactivity. Interactivity had proven to be a feature which consumers, especially collectors, favored when the movie studios had released their films on laser disk. When the price point for a laser disk at approximately $100 per disk moved to $20 per disk at retail, this luxury feature became available for mass consumption. Simultaneously the movie studios decided to change their home entertainment release model from a rental model to a for purchase model. This allowed all fans to become collectors and pushed the movie DVD into a demand position that essentially made it the most successful consumer product of all time. At the same time, a demand for interactive design talent and services was created. Movies in the past had uniquely designed title sequences. Suddenly every movie being released required information architecture and interactive design components that matched the film's tone and were at the quality level that Hollywood demanded for its product. Whole mini-studios to perform this type of work, such as 1K Studios and Canned Interactive, either formed or created service departments to fulfill this need in Hollywood. New DVD releases are released weekly by all major studios. DVDs are typically released on Tuesdays of every week. Sites such as FilmCrave display new DVD releases as they are released [18]. Information includes plots, actors, directors, release date and movie title. With the advent of Blu-ray releases, studios now rely on both Blu-ray and DVDs to supplement their revenue for a particular movie.

[edit]As

an interactive medium

DVD as a format had two qualities at the time that were not available in any other interactive medium: 1. Enough capacity and speed to provide high quality, full motion video and sound, and 2. low cost delivery mechanism provided by consumer products retailers who quickly moved to sell their players for under $200 and eventually for under $50 at retail. In addition, the medium itself was small enough and light enough to mail using general first class postage. Almost over night, this created a new business opportunity and model for business innovators like Netflix to re-invent the home entertainment distribution model. It also opened up the opportunity for business and product information to be inexpensively provided on full motion video through direct mail. Again, a demand for unique interactive design talent and services was created. Companies as large as Nike and Mattel went in search of new start-ups such as 1K Studios and Canned Interactive to fulfill their information architecture and design needs.

[edit]Capacity Capacity and nomenclature[19][20]
SS = single-sided, DS = double-sided, SL = single-layer, DL = dual-layer

(cm)

(GB)

(GiB )

DVD-1[21]

SS SL

1

1

8 1.46

1.36

DVD-2

SS DL

1

2

8 2.66

2.47

DVD-3

DS SL

2

2

8 2.92

2.72

DVD-4

DS DL

2

4

8 5.32

4.95

DVD-5

SS SL

1

1

12 4.70

4.37

DVD-9

SS DL

1

2

12 8.54

7.95

DVD-10

DS SL

2

2

12 9.40

8.75

DVD-14[22] DS SL+DL

2

3

12

13.2 12.33 4

DVD-18

DS DL

2

4

12

17.0 15.90 8

Capacity and nomenclature of (re)writable discs

(cm)

(GB)

(GiB )

DVD-R

SS SL (1.0) 1

1

12

3.95 3.68

DVD-R

SS SL (2.0) 1

1

12

4.70 4.37

DVD-RW

SS SL

1

1

12

4.70 4.37

DVD+R

SS SL

1

1

12

4.70 4.37

DVD+RW SS SL

1

1

12

4.70 4.37

DVD-R

DS SL

2

2

12

9.40 8.75

DVD-RW

DS SL

2

2

12

9.40 8.75

DVD+R

DS SL

2

2

12

9.40 8.75

DVD+RW DS SL

2

2

12

9.40 8.75

DVD-RAM SS SL

1

1

8

1.46 1.36*

DVD-RAM DS SL

2

2

8

2.65 2.47*

DVD-RAM SS SL (1.0) 1

1

12

2.58 2.40

DVD-RAM SS SL (2.0) 1

1

12

4.70 4.37

DVD-RAM DS SL (1.0) 2

2

12

5.16 4.80

DVD-RAM DS SL (2.0) 2

2

12

9.40 8.75*

The basic types of DVD (12 cm diameter, single-sided or homogeneous double-sided) are referred to by a rough approximation of their capacity in gigabytes. In draft versions of the specification, DVD-5 indeed held five gigabytes, but some parameters were changed later on as explained above, so the capacity decreased. Other formats, those with 8 cm diameter and hybrid variants, acquired similar numeric names with even larger deviation. The 12 cm type is a standard DVD, and the 8 cm variety is known as a MiniDVD. These are the same sizes as a standard CD and amini-CD, respectively. The capacity by surface (MiB/cm2) varies from 6.92 MiB/cm2 in the DVD-1 to 18.0 MiB/cm2 in the DVD-18. As with hard disk drives, in the DVD realm, gigabyte and the symbol GB are usually used in the SI sense (i.e., 109, or 1,000,000,000 bytes). For distinction, gibibyte (with symbol GiB) is used (i.e., 10243 (230), or 1,073,741,824 bytes).

Size comparison: a 12 cm DVD+RW and a 19 cm pencil.

Each DVD sector contains 2,418 bytes of data, 2,048 bytes of which are user data. There is a small difference in storage space between+ and - (hyphen) formats:

Capacity differences of writable DVD formats

Type

Sectors

Bytes

KB

MB

GB

KiB

MiB

GiB

DVD-R SL

2,298,49 4,707,319,80 4,707,319.80 4,707.32 4.70 4,596,99 4,489.25 4.38 6 8 8 0 7 2 0 4

DVD+R SL

2,295,10 4,700,372,99 4,700,372.99 4,700.37 4.70 4,590,20 4,482.62 4.37 4 2 2 3 0 8 5 8

DVD-R DL

4,171,71 8,543,666,17 8,543,666.17 8,543.66 8.54 8,343,42 8,147.87 7.95 2 6 6 6 4 4 5 7

DVD+R DL

4,173,82 8,547,991,55 8,547,991.55 8,547.99 8.54 8,347,64 8,152.00 7.96 4 2 2 2 8 8 0 1

[edit]Technology

DVD-RW Drive operating with the protective cover removed.

DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing for a DVD's increased storage capacity. In comparison, Blu-ray Disc, the successor to the DVD format, uses a wavelength of 405 nm, and one duallayer disc has a 50 GB storage capacity.

Writing speeds for DVD were 1×, that is, 1350 kB/s (1,318 KiB/s), in the first drives and media models. More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 153.6 kB/s (150 KiB/s), about one-ninth as swift.[21]

DVD drive speeds

(Mbit/s)

(MB/s)

(MiB/s )

SL

DL



10.80

1.35

1.29

61

107



21.60

2.70

2.57

31

54

2.4×

25.92

3.24

3.09

25

45

2.6×

28.08

3.51

3.35

23

41



43.20

5.40

5.15

15

27



64.80

8.10

7.72

10

18



86.40

10.80

10.30

8

13

10×

108.00

13.50

12.87

6

11

12×

129.60

16.20

15.45

5

9

16×

172.80

21.60

20.60

4

7

18×

194.40

24.30

23.17

3

6

20×

216.00

27.00

25.75

3

5

22×

237.60

29.70

28.32

3

5

24×

259.20

32.40

30.90

3

4

[edit]Internal

mechanism of a drive

See also: optical disc drive

Internal mechanism of a DVD-ROM Drive. See text for details.

This mechanism is shown right side up; the disc is above it. The laser and optical system "looks at" the underside of the disc. With reference to the photo, just to the right of image center is the disc spin motor, a gray cylinder, with its gray centering hub and black resilient drive ring on top. A clamp (not in the photo, retained in the drive's cover), pulled down by a magnet, clamps the disc when this mechanism rises, after the disc tray stops moving inward. This motor has an external rotor – every part of it that you can see spins. The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise when running fast. The soft shock mount grommets are just below the brass-colored washers at the four corners (the left one is obscured). Running through those grommets are screws to fasten them to the black plastic frame that's underneath. Two parallel precision 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. A dark gray disc with two holes on opposite sides has a blue lens surrounded by silver-colored metal. This is the lens that's closest to the disc; it serves to both read and write by focusing the laser light to a very small

spot. It's likely that this disc rotates half a turn to position a different set of optics (the other "hole") for CDs vs. DVDs. Under the disc is an ingenious actuator comprising permanent magnets and coils that move the lens up and down to maintain focus on the data layer. As well, the actuator moves the lens slightly toward and away from the spin-motor spindle to keep the spot on track. Both focus and tracking are relatively quite fast and very precise. The same actuator rotates the lens mount half a turn as described. To select tracks (or files) as well as advancing the "sled" during continuous read or write operations, a stepping motor rotates a coarse-pitch leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew, itself, is the rod with evenly-spaced darker details; these are the helical groove that engages a pin on the "sled". The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "flexible printed circuits" that connect everything to the electronics (which is not shown).

[edit]DVD

recordable and rewritable

Main article: DVD recordable

Faceplate of a DVD Drive supporting both DVD+ and DVD- formats.

HP initially developed recordable DVD media from the need to store data for backup and transport. DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW, DVD+R/RW (plus), and DVD-RAM. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with encrypted content but General discs may not.
[24]

Although most DVD writers can nowadays write the DVD+R/RW and DVD-R/RW formats (usually denoted by "DVD±RW" and/or the existence of both the DVD Forum logo and the DVD+RW Alliance logo), the "plus" and

the "dash" formats use different writing specifications. Most DVD readers and players will play both kinds of discs, although older models can have trouble with the "plus" variants.

[edit]Dual-layer

recording

Dual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.54gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. Along with this, DVD-DLs have slower write speeds as compared to ordinary DVDs and when played on a DVD player, a slight transition can be seen between the layers. DVD-R DL was developed for the DVD Forum by Pioneer Corporation;DVD+R DL was developed for the DVD+RW Alliance by Philips and Mitsubishi Kagaku Media (MKM).[25] A dual-layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds.[26] This caused some viewers to worry that their dual-layer discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual-layer pausing effect on all duallayer disc packaging. DVD recordable discs supporting this technology are backward-compatible with some existing DVD players and DVD-ROM drives.[25] Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, although the blank media remain more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media. There are two modes for dual-layer orientation. With Parallel Track Path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With Opposite Track Path (OTP), used on many Digital Video Discs, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends; they share one lead-in and one lead-out. However, some DVDs also use a parallel track, such as those authored episodically, as in a disc with several separate episodes of a TV series—where more often than not, the layer change is in-between titles and therefore would not need to be authored in the opposite track path fashion.[citation needed]

[edit]DVD-Video
Main article: DVD-Video DVD-Video is a standard for content on DVD media. The format went on sale in Japan on November 1, 1996, in the United States on March 1, 1997, in Europe on October 1, 1998 and in Australia on February 1, 1999.
[27]

DVD became the dominant form of home video distribution in Japan when it first went on sale in 1996, but

did not become the dominant form of home video distribution in the United States until June 15, 2003, when

weekly DVD-Video in the United States rentals began outnumbering weekly VHS cassette rentals, reflecting the rapid adoption rate of the technology in the U.S. marketplace.[5][28] Currently, DVD-Video is the dominant form of home video distribution worldwide, although in Japan it was surpassed by Blu-ray Disc when Blu-ray first went on sale in Japan on March 31, 2006. Although many resolutions and formats are supported, most consumer DVDs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720/704×480 (NTSC) or 720/704×576 (PAL) at 29.97, 25, or 23.976 FPS. Audio is commonly stored using the Dolby Digital (AC-3) or Digital Theater System (DTS) formats, ranging from 16-bits/48 kHz to 24-bits/96 kHz format with monaural to 6.1-channel "Surround Sound" presentation, and/or MPEG-1 Layer 2 and/or LPCM Stereophonic. Although the specifications for video and audio requirements vary by global region and television system, many DVD players support all possible formats. DVD Video also supports features such as menus, selectable subtitles, multiple camera angles, and multiple audio tracks.

[edit]Security
Main article: Content Scramble System

[edit]Consumer

rights

The rise of filesharing and "piracy" has prompted many copyright holders to display notices on DVD packaging or displayed on screen when the content is played that warn consumers of the illegality of certain uses of the DVD. It is commonplace to include a 90 second advert warning that most forms of copying the contents are illegal. Many DVDs prevent skipping past or fast-forwarding through this warning, forcing the consumer to watch. Arrangements for renting and lending differ by geography. In the U.S., the right to re-sell, rent, or lend out bought DVDs is protected by the first-sale doctrine under the Copyright Act of 1976. In Europe, rental and lending rights are more limited, under a 1992 European Directive that gives copyright holders broader powers to restrict the commercial renting and public lending of DVD copies of their work.

[edit]DVD-Audio
Main article: DVD-Audio DVD-Audio is a format for delivering high fidelity audio content on a DVD. It offers many channel configuration options (from mono to 5.1 surround sound) at various sampling frequencies (up to 24-bits/192 kHz versus CDDA's 16-bits/44.1 kHz). Compared with the CD format, the much higher-capacity DVD format enables the inclusion of considerably more music (with respect to total running time and quantity of songs) and/or far higher audio quality (reflected by higher sampling rates and greater sample resolution, and/or additional channels for spatial sound reproduction).

Despite DVD-Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable in typical listening environments. DVD-Audio currently forms a niche market, probably due to the very sort of format war with rival standard SACD that DVD-Video avoided.

[edit]Security
Main article: Content Protection for Recordable Media DVD-Audio discs employ a DRM mechanism, called Content Protection for Prerecorded Media (CPPM), developed by the 4C group (IBM, Intel, Matsushita, and Toshiba). Although CPPM was supposed to be much harder to crack than DVD-Video's CSS, it too was eventually cracked in 2007 with the release of the dvdcpxm tool. The subsequent release of the libdvdcpxm library (which is based on dvdcpxm) allowed for the development of open source DVD-Audio players and ripping software, such as DVD-Audio Explorer.[29] As a result, making 1:1 copies of DVD-Audio discs is now possible with relative ease, much like DVD-Video discs.

[edit]Improvements [edit]HD

and succession

DVD and Blu-ray Disc

In 2006, two new formats called HD DVD and Blu-ray Disc were released as the successor to DVD. HD DVD competed unsuccessfully with Blu-ray Disc in the format war of 2006–2008. A dual layer HD DVD can store up to 30GB and a dual layer Blu-ray disc can hold up to 50GB.[30][31] However, unlike previous format changes, e.g., audio tape to compact disc or VHS videotape to DVD, there is no immediate indication that production of the standard DVD will gradually wind down, as they still dominate, with around 87% of video sales and approximately one billion DVD player sales worldwide. In fact experts claim that the DVD will remain the dominant medium for at least another five years as Blu-ray technology is still in its introductory phase, write and read speeds being poor as well as the fact of necessary hardware being expensive and not readily available.[5][32] Consumers initially were also slow to adopt Blu-ray due to the cost.[33] By 2009, 85% of stores were selling Bluray Discs. A high-definition television and appropriate connection cables are also required to take advantage of Blu-ray disc. Some analysts suggest that the biggest obstacle to replacing DVD is due to its installed base; a large majority of consumers are satisfied with DVDs.[34] The DVD succeeded because it offered a compelling alternative to VHS. In addition, Blu-ray players are designed to be backward-compatible, allowing older DVDs to be played since the media are physically identical; this differed from the change from vinyl to CD and from tape to DVD, which involved a complete change in physical medium. As of 2011 it is still commonplace for major releases to be issued in "combo pack" format, including both a DVD and a Blu-ray disc (as well as, in many cases, a third disc with an authorized digital copy). Also, some multi-disc sets use Blu-ray for the main

feature, but DVD discs for supplementary features (examples of this include the Harry Potter "Ultimate Edition" collections, the 2009 re-release of the 1967 The Prisoner TV series, and a 2007 collection related to Blade Runner). This situation can be best compared to the changeover from 78 rpm shellac recordings to 45 rpm and 33⅓ rpm vinyl recordings; because the medium used for the earlier format was virtually the same as the latter version (a disc on a turntable, played using a needle), phonographs continued to be built to play obsolete 78s for decades after the format was discontinued. Manufacturers continue to release standard DVD titles as of 2011, and the format remains the preferred one for the release of older television programs and films, with some programs such as Star Trek: The Original Seriesneeding to be re-scanned to produce a high definition version from the original film recordings (certain special effects were also updated in order to be better received in highdefinition viewing).[35] In the case of Doctor Who, a series primarily produced on standard definition videotape between 1963 and 1989, BBC Video reportedly intends to continue issuing DVD-format releases of that series until at least November 2013 (since there would be very little increase in visual quality from upconverting the standard definition videotape masters to high definition).[36]

[edit]Holographic

Versatile Disc

The Holographic Versatile Disc (HVD) is an optical disc technology that may one day hold up to 4 terabytes (TB) of information, although the current maximum is 500GB. It employs a technique known as collinear holography.

[edit]5D

DVD

The 5D DVD, being developed in the Swinburne University of Technology in Melbourne, Australia, uses a multilaser system to encode and read data on multiple layers. Disc capacities are estimated at up to 10 terabytes, and the technology could be commercially ready within ten years.[37]

[edit]Use

as backup medium

Durability of DVDs is measured by how long the data may be read from the disc, assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Five factors affect durability: sealing method, reflective layer, organic dye makeup, where it was manufactured, and storage practices.[38] The longevity of the ability to read from a DVD+R or DVD-R, is largely dependent on manufacturing quality ranging from 2 to 15 years,[39][40][41] and is believed to be an unreliable medium for backup unless great care is taken for storage conditions and handling. According to the Optical Storage Technology Association (OSTA), "manufacturers claim life spans ranging from 30 to 100 years for DVD, DVD-R and DVD+R discs and up to 30 years for DVD-RW, DVD+RW and DVDRAM".[42]

Compact Disc shattering
From Wikipedia, the free encyclopedia
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Piece of exploded CD

Exploded CD

CD shattering, DVD shattering (more recently Blu-ray shattering) and optical disc shattering , a phenomenon also known as exploding CDs, occurs when a CD shatters inside a high speed optical disc drive (48X or higher CD-ROM unit) with a loud cracking sound. Typically, the disc and the drive will be ruined. Fragments of the broken disc may be expelled through the front of the drive at high speed and cause physical injury. Maxell's senior marketing manager, Dawn Wortman has been quoted as saying there is very little danger at 48x, and danger of shattering only becomes significant above 48x (or 52x). "The 48X standard offers customers outstanding performance without the risks associated with 52X speeds," says Dawn Wortman. A disc shatters when it fails to support the centripetal force required to keep all parts of the disc moving circularly. The velocity of the edge of a 120 mm disc rotating at 10,350 RPM is approximately 65 m/s. (234.1 km/h, 145.5 mph) To remain in circular motion about the spindle, the disc edge accelerates at about 7,200 G. The force causing this acceleration is transmitted through the disc itself and is balanced by an opposite force on the other side of the disc. Thus, a disc begins to fail when it can not handle these forces, and a failing disc can then completely shatter due to the imbalance of forces around the disc. The television series MythBusters conducted experiments in which they succeeded in shattering otherwise undamaged control CDs at speeds in excess of 23,000 RPM. A 52x drive using CLV needs to go up to 27,500 RPM when reading the inner track, however very few drives reach those speeds, reading data at a slower rate on inner tracks and only achieving 52x read speeds on the outer track. (In other words 52x is the peak read speed, not the typical rate.) Typically a 52x drive will actually max at around 11,500 RPM. At this speed it is still possible for a CD to shatter with enough force to come flying out of a drive. When brittle media is put in the drive, small cracks can occur on

the inner hole of the disc. Once these cracks reach a critical length, they propagate in an instant and the disc shatters. The critical length of the crack is a function of the rotational speed. If the drive is spinning below 8,000 rpm or around 40x the critical length of the crack is long enough that the crack enters the disc media before becoming critical. At this point the crack enters the media, the drive detects the error and slows down. Many drive manufacturers now have more aggressive back-off algorithms that detect issues with the disc and this reduces the chance of the disc shattering. Some companies also deliberately slow their drive down to 40x and the user has to press a combination of buttons to allow 52x speed to be reached. In doing so, the user takes the responsibility for any issues arising from disc shattering.

Optical disc drive
From Wikipedia, the free encyclopedia

A CD-ROM Drive

A CD-ROM Drive (without case)

Optical discs




Optical disc Optical disc drive Optical disc authoring Authoring software Recording technologies

  

 

Recording modes Packet writing Optical media types

 

Blu-ray Disc (BD): BD-R, BD-RE DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-R DS, DVD+R DS, DVD-RW,DVD+RW, DVD-RAM, DVDD, HVD, EcoDisc



Compact Disc (CD): Red Book, CD-ROM,CD-R, CD-RW, 5.1 Music Disc, SACD,PhotoCD, CD Video (CDV), Video CD (VCD),SVCD, CD+G, CD-Text, CD-ROM XA, CD-i

            

Universal Media Disc (UMD) Enhanced Versatile Disc (EVD) Forward Versatile Disc (FVD) Holographic Versatile Disc (HVD) China Blue High-definition Disc (CBHD) HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM High definition Versatile Multilayer Disc (HD VMD) VCDHD GD-ROM MiniDisc (MD) (Hi-MD) Laserdisc (LD) Video Single Disc (VSD) Ultra Density Optical (UDO)

  

Stacked Volumetric Optical Disk (SVOD) Five dimensional discs (5D DVD) Nintendo optical disc (NOD) Standards




Rainbow Books File systems



ISO 9660

    

Joliet Rock Ridge / SUSP El Torito Apple ISO 9660 Extensions

Universal Disk Format (UDF)



Mount Rainier See also

 

History of optical storage media High definition optical disc format war
This box: view · talk · edit

The CD/DVD drive lens on an Acer laptop

In computing, an optical disc drive (ODD) is a disk drive that uses laser light or electromagnetic waves near the light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can

only read from discs, but recent drives are commonly both readersand recorders. Recorders are sometimes called burners or writers. Compact discs, DVDs, and Blu-ray discs are common types of optical media which can be read and recorded by such drives. Optical disc drives are an integral part of stand-alone consumer appliances such as CD players, DVD players and DVD recorders. They are also very commonly used in computers to read software and consumer media distributed in disc form, and to record discs for archival and data exchange. Optical drives—along with flash memory—have mostly displaced floppy disk drives and magnetic tape drives for this purpose because of the low cost of optical media and the near-ubiquity of optical drives in computers and consumer entertainment hardware. Disc recording is generally restricted to small-scale backup and distribution, being slower and more materially expensive per unit than the moulding process used to mass-manufacture pressed discs.
Contents
[hide]

• • • • • • •

1 Laser and optics 2 Rotational mechanism 3 Loading mechanisms 4 Computer interfaces 5 Compatibility 6 Recording performance 7 Recording schemes

○ ○ ○

7.1 Recorder Unique Identifier 7.2 Source IDentification Code 7.3 Use of RID and SID together in forensics

• • •

8 See also 9 References 10 External links

[edit]Laser

and optics

The most important part of an optical disc drive is an optical path, placed in a pickup head (PUH),[1] usually consisting of semiconductor laser, a lens for guiding the laser beam, and photodiodes detecting the light reflection from disc's surface.[2] Initially, CAT lasers with a wavelength of 780 nm were used, being within infrared range. For DVDs, the wavelength was reduced to 650 nm (red color), and the wavelength for Blu-Ray Disc was reduced to 405 nm (violet color). Two main servomechanisms are used, the first one to maintain a correct distance between lens and disc, and ensure the laser beam is focused on a smalllaser spot on the disc. The second servo moves a head along the disc's radius, keeping the beam on a groove, a continuous spiral data path. On read only media (ROM), during the manufacturing process the groove, made of pits, is pressed on a flat surface, called land. 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 reading beam, causing mutual destructive interference and reducing the reflected beam's intensity. This is detected by photodiodes that output electrical signals. A recorder encodes (or burns) data onto a recordable CD-R, DVD-R, DVD+R, or BD-R disc (called a blank) by selectively heating parts of an organic dyelayer with a laser[citation needed]. 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. The higher 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. 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 anamorphous form, enabling marks of varying reflectivity to be created. 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. Double 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 starts on the outer edge and extends inwards. Some drives support Hewlett-Packard's LightScribe photothermal printing technology for labeling specially coated discs.

[edit]Rotational

mechanism

Optical drives' rotational mechanism differs considerably from hard disk drives', in that the latter keep 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 an outer disc area, as compared to inner area. 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 is wasted, a head had to transfer data at a maximum linear rate at all times too, without slowing on the outer rim of disc. This had led to optical drives—until recently —operating with aconstant linear velocity (CLV). The spiral groove of the disc passed under its head at a constant speed. Of course the implication of CLV, as opposed to CAV, is that disc angular velocity is no longer constant, and spindle motor need to be designed to vary speed between 200 RPM on the outer rim and 500 RPM on the inner rim. 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 4X drive, for instance, would rotate at 800-2000 RPM, while transferring data steadily at 600 KiB/s, which is equal to 4 x 150 KiB/s. For DVD base speed, or "1x speed", is 1.385 MB/s, equal to 1.32 MiB/s, approximately 9 times faster than CD's base speed. For Blu-ray drive base speed is 6.74 MB/s, equal to 6.43 MiB/s. There are mechanical limits to how quickly a disc can be spun. Beyond a certain rate of rotation, around 10000 RPM, centrifugal stress can cause the disc plastic to creep and possibly shatter. On the outer edge of the CD disc, 10000 RPM limitation roughly equals to 52x speed, but on the inner edge only to 20x. Some drives further lower their maximum read speed to around 40x on the reasoning that blank discs will be clear of structural damage, but that discs inserted for reading may not be. Without higher rotational speeds, increased read performance may be attainable by simultaneously reading more than one point of a data groove [3], but drives with such mechanisms are more expensive, less compatible, and very uncommon.

The Z-CLV recording strategy is easily visible after burning a DVD-R.

Because keeping a constant transfer rate for the whole disc is not so important in most contemporary CD uses, to keep the rotational speed of the disc safely low while maximizing data rate, a pure CLV approach needed to be abandoned. Some drives work in 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 different constant linear velocity. A Z-CLV recorder rated at "52X", for example, would write at 52X on the innermost zone and then progressively decrease the speed in several discrete steps down to 20X at the outer rim.

[edit]Loading

mechanisms

Current optical drives use either a tray-loading mechanism, where the disc is loaded onto a motorised or manually operated tray, or a slot-loading mechanism, where the disc is slid into a slot and drawn in by motorized rollers. Slot-loading drives have the disadvantage that they cannot usually accept the smaller 80 mm discs or any non-standard sizes; however, the Wii and PlayStation 3 video game consoles seem to have defeated this problem, for they are able to load standard size DVDs and 80 mm discs in the same slot-loading drive.[citation needed] A small number of drive models, mostly compact portable units, have a top-loading mechanism where the drive lid is opened upwards and the disc is placed directly onto the spindle.[4] (for example, all PlayStation 1 consoles, portable CD players, and some standalone CD recorders all 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. 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"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.

[edit]Computer

interfaces

Digital audio output, analog audio output, and parallel ATA interface.

Most internal drives for personal computers, servers and workstations are designed to fit in a standard 5.25" drive bay and connect to their host via anATA or SATA interface. Additionally, there may be digital and analog outputs for Red Book audio. The outputs may be connected via a header cable to the sound card or the motherboard. At one time, computer software resembling cd players controlled playback of the CD. Today the information isextracted from the disc as data, to be played back or converted to other file formats. External drives usually have USB or FireWire interfaces. Some portable versions for laptop use power themselves off batteries or off their interface bus. Drives with SCSI interface exist, but are less common and tend to be more expensive, because of the cost of their interface chipsets and more complex SCSI connectors. 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 3.5" floppy and 3.5" hard disk, and did not include a place for a large internal device. Also IBM PCs and clones at first only included a single ATA drive interface, which by the time the CDROM was introduced, was already being used to support two hard drives. Early laptops simply had no built-in high-speed interface for supporting an external storage device. This was solved through several techniques:



Early sound cards could include a second ATA interface, though it was often limited to supporting a single optical drive and no hard drives. This evolved into the modern second ATA interface included as standard equipment



A parallel port external drive was developed that connected between a printer and the computer. This was slow but an option for laptops




A PCMCIA optical drive interface was also developed for laptops A SCSI card could be installed in desktop PCs for an external SCSI drive enclosure, though SCSI was typically much more expensive than other options

[edit]Compatibility
Most optical drives are backwards compatible with their ancestors up to CD, although this is not required by standards. 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.

Press ed CD

CDR

CDRW

Press Press DVD BD- BDDVD DVD DVD DVD+R ed BD- BDed +R R RE -R +R -RW W CAT R RE DVD DL DL DL BD

Audio CD player

Read

Read Read
1 2

None None None

None None

None

None

Non Non Non Non e e e e

CD-ROM driv Read e

Read Read
1 2

None None None

None None

None

None

Non Non Non Non e e e e

CD-R recorder Read

Write Read None None None

None None

None

None

Non Non Non Non e e e e

CD-RW record Read er

Write Write None None None

None None

None

None

Non Non Non Non e e e e

DVD-ROM dri Read ve

Read Read
3 3

Read

Read
4

Read 4

Read
4

Read 4

Read 5 None

Non Non Non Non e e e e

DVD-R record Read er

Write Write Read

Write Read 6

Read
7

Read 6

Read 5 None

Non Non Non Non e e e e

DVD-RW reco Read rder

Write Write Read

Write Read 7

Write
8

Read 6

Read 5 None

Non Non Non Non e e e e

DVD+R record Read er

Write Write Read

Read
6

Write

Read
6

Read 9

Read 5 None

Non Non Non Non e e e e

DVD+RW rec Read order

Write Write Read

Read
6

Write

Read
6

Write

Read 5 None

Non Non Non Non e e e e

DVD±RW recorder

Read

Write Write Read

Write Write Write Write

Read 5 None

Non Non Non Non e e e e

DVD±RW/DV D+R DL Read recorder

Write Write Read

Write
10

Write

Write
10

Write

Write None

Non Non Non Non e e e e

BD-ROM

Read

Read Read Read

Read Read

Read Read

Read

Read

Rea Rea Rea Rea d d d d

BD-R recorder

Read
11

Write Write
11 11

Read

Write Write Write Write

Write Read

Wri Rea Rea Rea te d d d

BD-RE recorder

Read
11

Write Write
11 11

Read

Write Write Write Write

Write Read

Wri Wri Rea Rea te te d d

BD-R DL recorder

Read
11

Write Write
11 11

Read

Write Write Write Write

Write Read

Wri Rea Wri Rea te d te d

BD-RE DL recorder

Read
11

Write Write
11 11

Read

Write Write Write Write

Write Read

Wri Wri Wri Wri te te te te

   

^1 Some types of CD-R media with less-reflective dyes may cause problems. ^2 May not work in non MultiRead-compliant drives. ^3 May not work in some early-model DVD-ROM drives. ^4 A large-scale compatibility test conducted by cdrinfo.com in July 2003 found DVD-R discs playable by 96.74%, DVD+R by 87.32%, DVD-RW by 87.68% and DVD+RW by 86.96% of consumer DVD players and DVDROM drives.



^5 Read compatibility with existing DVD drives may vary greatly] with the brand of DVD+R DL media used.

     

^6 Need information on read compatibility. ^7 May not work in non DVD Multi-compliant drives. ^8 Recorder firmware may blacklist or otherwise refuse to record to some brands of DVD-RW media. ^9 Need information on read compatibility. ^10 As of April 2005, all DVD+R DL recorders on the market are Super Multi-capable. ^11 As of October 2006, recently released BD drives are able to read and write CD media.

[edit]Recording

performance

Optical recorder drives are often marked with three different speed ratings. In these cases, the first speed is for write-once (R) operations, second for re-write (RW or RE) operations, and one for read-only (ROM) operations. For example a 12x/10x/32x CD drive is capable of writing to CD-R discs at 12x speed (1.76 MB/s), write to CDRW discs at 10x speed (1.46 MB/s), and read from any CD discs at 32x speed (4.69 MB/s). 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. 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 12X and 16X.

[edit]Recording

schemes

See also: Optical disc recording technologies 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. 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 DVDROM 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. 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 thirdparty drivers. The DVD+RW disc format goes further by embedding more accurate timing hints in the data groove of the disc and allowing individual data blocks to be replaced without affecting backwards 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. 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.

[edit]Recorder

Unique Identifier

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." [5] 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.

[edit]Source

IDentification Code

The Source IDentification Code (SID) is an eight character supplier code that is placed on every CD-ROM. The SID identifies not only manufacturer, the individual factory, and even the machine that produced the (blank, writeable) disc. Quoting Philips: "The Source IDentification Code (SID Code) provides an optical disc production facility with the means to identify:

 

all discs mastered and/or replicated in its plant; and the individual Laser Beam Recorder (LBR) signal processor or mould that produced a particular stamper or disc."

[5]

[edit]Use

of RID and SID together in forensics

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. [6]

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