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A CD-ROM
CD-ROM
/ˌsiːˌdiːˈrɒm/ is a pre-pressed optical compact disc which contains data. The name is an acronym which stands for "Compact Disc Read-Only Memory". Computers can read CD-ROMs, but cannot write to CD-ROMs, which are not writable or erasable. During the 1990s, CD-ROMs were popularly used to distribute software for computers and video game consoles. Some CDs, called enhanced 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[2] format PC CD-ROMs). The CD-ROM
CD-ROM
format was developed by Japanese company Denon
Denon
in 1982. It was an extension of Compact Disc Digital Audio, and adapted the format to hold any form of digital data, with a storage capacity of 553 MiB.[3] CD-ROM
CD-ROM
was then introduced by Denon
Denon
and Sony
Sony
at a Japanese computer show in 1984.[4] The Yellow Book is the technical standard that defines the format of CD-ROMs. One of a set of color-bound books that contain the technical specifications for all CD formats, the Yellow Book, standardized by Sony
Sony
and Philips
Philips
in 1983, has a capacity of 650 MiB.

Contents

1 CD-ROM
CD-ROM
discs

1.1 Media 1.2 Standard 1.3 CD-ROM
CD-ROM
format 1.4 CD-ROM XA
CD-ROM XA
extension 1.5 Disc images 1.6 Manufacture 1.7 Capacity

2 CD-ROM
CD-ROM
drives

2.1 Laser
Laser
and optics 2.2 Transfer rates

3 Copyright issues 4 See also 5 Notes 6 References

CD-ROM
CD-ROM
discs[edit] Media[edit]

A CD-ROM
CD-ROM
in the tray of a partially open DVD-ROM
DVD-ROM
drive.

CD-ROMs 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 is 120 mm in diameter, though the smaller Mini CD
Mini CD
standard with an 80 mm diameter, as well as shaped compact discs in numerous non-standard sizes and molds (e.g., business card-sized media), are also available.[citation needed] 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 reflected beam'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. Standard[edit] Several formats are used for data stored on compact discs, known as the Rainbow Books. The Yellow Book, published in 1988,[5] defines the specifications for CD-ROMs, standardized in 1989 as the ISO/IEC 10149 / ECMA-130 standard. The CD-ROM
CD-ROM
standard builds on top of the original Red Book CD-DA standard for CD audio. Other standards, such as the White Book for Video CDs, further define formats based on the CD-ROM specifications. The Yellow Book itself is not freely available, but the standards with the corresponding content can be downloaded for free from ISO[1] or ECMA.[6] There are several standards that define how to structure data files on a CD-ROM. ISO 9660
ISO 9660
defines the standard file system for a CD-ROM. ISO 13490 is an improvement on this standard which adds support for non-sequential write-once and re-writeable discs such as CD-R
CD-R
and CD-RW, as well as multiple sessions. The ISO 13346 standard was designed to address most of the shortcomings of ISO 9660,[7] and a subset of it evolved into the UDF format, which was adopted for DVDs. The bootable CD specification was issued in January 1995, to make a CD emulate a hard disk or floppy disk, and is called El Torito. CD-ROM
CD-ROM
format[edit] Data stored on CD-ROMs follows the standard CD data encoding techniques described in the Red Book specification (originally defined for audio CD only). This includes cross-interleaved Reed–Solomon coding (CIRC), eight-to-fourteen modulation (EFM), and the use of pits and lands for coding the bits into the physical surface of the CD. The structures used to group data on a CD-ROM
CD-ROM
are also derived from the Red Book. Like audio CDs (CD-DA), a CD-ROM
CD-ROM
sector contains 2,352 bytes of user data, composed of 98 frames, each consisting of 33-bytes (24 bytes for the user data, 8 bytes for error correction, and 1 byte for the subcode). Unlike audio CDs, the data stored in these sectors corresponds to any type of digital data, not audio samples encoded according to the audio CD specification. To structure, address and protect this data, the CD-ROM
CD-ROM
standard further defines two sector modes, Mode 1 and Mode 2, which describe two different layouts for the data inside a sector.[2] A track (a group of sectors) inside a CD-ROM only contains sectors in the same mode, but if multiple tracks are present in a CD-ROM, each track can have its sectors in a different mode from the rest of the tracks. They can also coexist with audio CD tracks as well, which is the case of mixed mode CDs. Both Mode 1 and 2 sectors use the first 16 bytes for header information, but differ in the remaining 2,336 bytes due to the use of error correction bytes. Unlike an audio CD, a CD-ROM
CD-ROM
cannot rely on error concealment by interpolation; a higher reliability of the retrieved data is required. To achieve improved error correction and detection, Mode 1, used mostly for digital data, adds a 32-bit cyclic redundancy check (CRC) code for error detection, and a third layer of Reed–Solomon error correction[n 1] using a Reed-Solomon Product-like Code (RSPC). Mode 1 therefore contains 288 bytes per sector for error detection and correction, leaving 2,048 bytes per sector available for data. Mode 2, which is more appropriate for image or video data (where perfect reliability may be a little bit less important), contains no additional error detection or correction bytes, having therefore 2,336 available data bytes per sector. Note that both modes, like audio CDs, still benefit from the lower layers of error correction at the frame level.[8] Before being stored on a disc with the techniques described above, each CD-ROM
CD-ROM
sector is scrambled to prevent some problematic patterns from showing up.[6] These scrambled sectors then follow the same encoding process described in the Red Book in order to be finally stored on a CD. The following table shows a comparison of the structure of sectors in CD-DA and CD-ROMs:[6]

Format ← 2,352 byte sector structure →

CD digital audio: 2,352 (Digital audio)

CD-ROM
CD-ROM
Mode 1: 12 (Sync pattern) 3 (Address) 1 (Mode, 0x01) 2,048 (Data) 4 (Error detection) 8 (Reserved, zero) 276 (Error correction)

CD-ROM
CD-ROM
Mode 2: 12 (Sync pattern) 3 (Address) 1 (Mode, 0x02) 2,336 (Data)

The net byte rate of a Mode-1 CD-ROM, based on comparison to CD-DA audio standards, is 44,100 Hz × 16 bits/sample × 2 channels × 2,048 / 2,352 / 8 = 153.6 kB/s = 150 KiB/s. This value, 150 KiB/s, is defined as "1× speed". Therefore, for Mode 1 CD-ROMs, a 1× CD-ROM drive reads 150/2 = 75 consecutive sectors per second. The playing time of a standard CD is 74 minutes, or 4,440 seconds, contained in 333,000 blocks or sectors. Therefore, the net capacity of a Mode-1 CD-ROM
CD-ROM
is 682 MB or, equivalently, 650 MiB. For 80 minute CDs, the capacity is 737 MB (703 MiB). CD-ROM XA
CD-ROM XA
extension[edit] CD-ROM XA
CD-ROM XA
is an extension of the Yellow Book standard for CD-ROMs that combines compressed audio, video and computer data, allowing all to be accessed simultaneously.[9] It was intended as a bridge between CD-ROM and CD-i
CD-i
(Green Book) and was published by Sony
Sony
and Philips
Philips
in 1991.[5] "XA" stands for eXtended Architecture. CD-ROM XA
CD-ROM XA
defines two new sector layouts, called Mode 2 Form 1 and Mode 2 Form 2 (which are different from the original Mode 2). XA Mode 2 Form 1 is similar to the Mode 1 structure described above, and can interleave with XA Mode 2 Form 2 sectors; it is used for data. XA Mode 2 Form 2 has 2,324 bytes of user data, and is similar to the standard Mode 2 but with error detection bytes added (though no error correction). It can interleave with XA Mode 2 Form 1 sectors, and it is used for audio/video data.[8] Video CDs, Super Video CDs, Photo CDs, Enhanced Music CDs and CD-i
CD-i
use these sector modes.[10] The following table shows a comparison of the structure of sectors in CD-ROM XA
CD-ROM XA
modes:

Format ← 2,352 byte sector structure →

CD-ROM XA
CD-ROM XA
Mode 2, Form 1: 12 (Sync pattern) 3 (Address) 1 (Mode) 8 (Subheader) 2,048 (Data) 4 (Error detection) 276 (Error correction)

CD-ROM XA
CD-ROM XA
Mode 2, Form 2: 12 (Sync pattern) 3 (Address) 1 (Mode) 8 (Subheader) 2,324 (Data) 4 (Error detection)

Disc images[edit] When a disc image of a CD-ROM
CD-ROM
is created, this can be done in either "raw" mode (extracting 2,352 bytes per sector, independent of the internal structure), or obtaining only the sector's useful data (2,048/2,336/2,352/2,324 bytes depending on the CD-ROM
CD-ROM
mode). The file size of a disc image created in raw mode is always a multiple of 2,352 bytes (the size of a block).[11] Disc image formats that store raw CD-ROM
CD-ROM
sectors include CCD/IMG, CUE/BIN, and MDS/MDF. The size of a disc image created from the data in the sectors will depend on the type of sectors it is using. For example, if a CD-ROM
CD-ROM
mode 1 image is created by extracting only each sector's data, its size will be a multiple of 2,048; this is usually the case for ISO disc images. On a 74-minute CD-R, it is possible to fit larger disc 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 MiB Red Book CD. The 14.8% increase is due to the discarding of error correction data. Manufacture[edit] 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". Capacity[edit]

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

CD-ROM
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
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
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)

Type Sectors Data (mode 1) max. size Audio max. size Time

(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.

CD-ROM
CD-ROM
drives[edit]

This section needs expansion with: Information on access time latency. You can help by adding to it. (June 2014)

Further information: Optical disc
Optical disc
drive

A view of a CD-ROM
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-ROM
CD-ROM
drive

CD-ROM
CD-ROM
discs are read using CD-ROM
CD-ROM
drives. A CD-ROM
CD-ROM
drive may be connected to the computer via an IDE (ATA), SCSI, SATA, FireWire, or USB interface or a proprietary interface, such as the Panasonic CD interface, LMSI/Philips, Sony
Sony
and Mitsumi standards, . Virtually all modern CD-ROM
CD-ROM
drives can also play audio CDs (as well as Video CDs and other data standards) when used with the right software. Laser
Laser
and optics[edit] CD-ROM
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. Transfer rates[edit] CD-ROM
CD-ROM
drives are rated with a speed factor relative to music CDs. If a CD-ROM
CD-ROM
is read at the same rotational speed as an audio CD, the data transfer rate is 150 KiB/s, commonly called "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. The 1× speed rating for CD-ROM (150 KiB/s) is different from the 1× speed rating for DVDs (1.32 MiB/s). By increasing the speed at which the disc is spun, data can be transferred at greater rates. For example, a CD-ROM
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
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
Samsung
Electronics introduced the SCR-3230, a 32x CD-ROM
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 using multiple laser pickups as demonstrated by the Kenwood TrueX 72× which uses seven laser beams and a rotation speed of approximately 10×. The first 12× drive was released in late 1996.[12] Above 12× speed, there are problems with vibration and heat. 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 limits on achievable symmetry and strength in mass-produced media, mean that CD-ROM
CD-ROM
drive speeds have not massively increased since the late 1990s. 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 10,000–13,000 rpm (i.e. 40–52× CAV). High rotational speeds also produce undesirable noise from disc vibration, rushing air and the spindle motor itself. 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 numerous sequential read errors and retries are encountered. Other methods of improving read speed were trialled such as using multiple optical beams, 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 DVD-ROM
DVD-ROM
drives capable of consistent 36× CD-ROM
CD-ROM
speeds (4× DVD) or higher. Additionally, with a 700 MB CD-ROM
CD-ROM
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 8.5 GiB (single and dual layer), with higher speed and capacity needs instead being catered to by Blu-ray
Blu-ray
drives. 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
CD-R
discs at 12× speed (1.76 MiB/s), write to CD-RW
CD-RW
discs at 10× speed (1.46 MiB/s), and read from CDs at 32× speed (4.69 MiB/s).

Common data transfer speeds for CD-ROM
CD-ROM
drives

Transfer speed KiB/s Mbit/s MiB/s [n 2] RPM

1× 150 1.2288 0.146 200–500

2× 300 2.4576 0.293 400-1,000

4× 600 4.9152 0.586 800–2,000

8× 1,200 9.8304 1.17 1,600–4,000

10× 1,500 12.288 1.46 2,000–5,000

12× 1,800 14.7456 1.76 2,400–6,000

20× 1,200–3,000 up to 24.576 up to 2.93 4,000 (CAV)

32× 1,920–4,800 up to 39.3216 up to 4.69 6,400 (CAV)

36× 2,160–5,400 up to 44.2368 up to 5.27 7,200 (CAV)

40× 2,400–6,000 up to 49.152 up to 5.86 8,000 (CAV)

48× 2,880–7,200 up to 58.9824 up to 7.03 9,600 (CAV)

52× 3,120–7,800 up to 63.8976 up to 7.62 10,400 (CAV)

56× 3,360–8,400 up to 68.8128 up to 8.20 11,200 (CAV)

72× 6,750–10,800 up to 88.4736 up to 10.5 2,000 (multi-beam)

Copyright issues[edit] Main article: Compact Disc and DVD
DVD
copy protection Software
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
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
CD-ROM
drive.[citation needed] Manufacturers of CD writers ( CD-R
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.[13] This is a counterpart to the Source Identification Code (SID), an eight character code beginning with "IFPI" that is usually stamped on discs produced by CD recording plants. See also[edit]

CD/ DVD
DVD
authoring Compact Disc Digital Audio Computer hardware DVD-Audio DVD-ROM MultiLevel Recording Optical disc
Optical disc
drive Phase-change Dual Thor-CD DVP Media, patent holder for self-loading and self configuring CD-ROM technology

Notes[edit]

^ Note that the CIRC error correction system used in the CD audio format has two interleaved layers. ^ To three significant figures.

References[edit]

^ a b ISO (1995). "ISO/IEC 10149:1995 – Information technology – Data interchange on read-only 120 mm optical data disks (CD-ROM)". Retrieved 2010-08-06.  ^ a b "CD Yellow Book Standards". www.mediatechnics.com. Retrieved 2015-11-16.  ^ Videodisc Update, Volumes 1-3, page 13, 1982 ^ Japanese PCs (1984) (14:24), Computer Chronicles ^ a b "What is Yellow Book?". Searchstorage.techtarget.com. Retrieved 2013-09-23.  ^ a b c "Data Interchange on Read-only 120 mm Optical Data Disks (CD-ROM)". ECMA. June 1996. Retrieved 2009-04-26.  ^ "Birth Announcement: ISO/IEC 13346 and ISO/IEC 13490". Standards.com. Retrieved 2013-09-23.  ^ a b McFadden, Andy (2002-12-20). "What is XA? CDPLUS? CD-i? MODE1 vs MODE2? Red/yellow/blue book?". CD-Recordable FAQ. Retrieved 2008-05-04.  ^ What are CD-ROM
CD-ROM
Mode-1, Mode-2 and XA? Archived 2013-01-26 at the Wayback Machine., Sony
Sony
Storage Support ^ "Gateway Support - What is CD-ROM/XA?". Support.gateway.com. Retrieved 2013-09-23.  ^ "Optical Media FAQs" (PDF). Archived from the original (PDF) on 2006-10-22. Retrieved 2007-01-06.  ^ "Gadget". Next Generation. No. 25. Imagine Media. January 1997. p. 30. Here comes Diamond with the first 12X CD-ROM.  ^ Schoen, Seth (July 20, 2007). "Harry Potter and the Digital Fingerprints". Electronic Frontier Foundation. Retrieved October 24, 2007. 

v t e

Rainbow Books

Red Book

CD-DA CD-Text CD+G CD+EG

Green Book

CD-i CD-i
CD-i
Ready

Yellow Book

CD-ROM CD-ROM
CD-ROM
XA Mixed Mode CD

Orange Book

CD-MO CD-R CD-RW

White Book

VCD SVCD CD-i
CD-i
Bridge

Blue Book

E-CD/CD+

Beige Book

PCD

Scarlet Book

SACD

Purple Book

DDCD

Black Book

Non-Standard Disc Format

v t e

Standards of Ecma International

Application interfaces

ANSI escape code Common Language Infrastructure Office Open XML OpenXPS

File
File
systems (tape)

Advanced Intelligent Tape DDS DLT Super DLT Holographic Versatile Disc Linear Tape-Open
Linear Tape-Open
(Ultrium-1) VXA

File
File
systems (disk)

CD-ROM CD File
File
System (CDFS) FAT

FAT12 FAT16 FAT16B

FD UDF Ultra Density Optical Universal Media Disc

Graphics

Universal 3D

Programming languages

C++/CLI C# Eiffel JavaScript
JavaScript
(E4X, ECMAScript)

Radio link interfaces

NFC UWB

Other

ECMA-35

List of Ecma standards (1961 - Present)

v t e

Compact disc

Discs

CD CD-DA

Red Book

CD-R

Orange Book

CD-ROM

Yellow Book

CD-RW CD-MRW CD-MO CD-i

Green Book

CD-Text CD+

Blue Book

CD+EG CD+G
CD+G
(Karaoke) Gold CD MiniCD Mixed Mode CD Photo CD

Beige Book

PMCD shaped CD

business card CD

SVCD VCD

White Book

Technology

Rainbow Books CD authoring CD burning CD copy protection CD emulation CD manufacturing CD ripping CD rot

CD bronzing

CD subcode C2 error CD-i
CD-i
Ready 4ch CD-DA El Torito ISO 9660

Joliet Romeo Rock Ridge ISO 13490

UDF XRCD

Hardware/Software/Content

CD Case CD drive CD player

Portable CD player

CD recorder CD ripper CD single

Mini CD
Mini CD
single

Court cases

Orange-Book-Standard

Lists

CD copy protection schemes CD player
CD player
manufacturers Optical disc
Optical disc
authoring software

Variants based on CD

5.1 Music Disc Black Book CD Video

Video Single Disc

cDVD CDVU+ DD-CD

Purple Book

DSD-CD DualDisc HDCD Hybrid DVD-Audio Hybrid SACD

Scarlet Book

MovieCD MP3 CD Picture CD VinylDisc

See also

Blu-ray DVD HD DVD LaserDisc MiniDisc SACD UMD WORM

Category Commons Wiktionary

Authority control

GN

.