What Is The Size Of A Cd Case

Pre-pressed compact disc containing computer data

CD-ROM
A traditional CD-ROM
Media type	Optical disc
Encoding	Various
Capacity	194 MB (8 cm), 553–900 MB (12 cm)
Readmachinery	600-780nm laser diode, 150 KB/south (i×; 150 × 2^ten), 10,800 KB/due south (72×)
Writemechanism	Pressed mold
Standard	ISO/IEC 10149^[ane]
Usage	Data storage

A CD-ROM (, compact disc read-only memory) is a pre-pressed optical meaty disc that contains data. Computers tin read—but not write or erase—CD-ROMs, i.e. it is a blazon of read-only retention. Some CDs, called enhanced CDs, agree both computer data and audio with the latter capable of being played on a CD player, while data (such equally software or digital video) is just usable on a computer (such every bit ISO 9660^[2] format PC CD-ROMs).

During the 1990s, CD-ROMs were popularly used to distribute software and data for computers and fifth generation video game consoles.

History [edit]

The earliest theoretical work on optical disc storage was washed past independent researchers in the The states including David Paul Gregg (1958) and James Russel (1965–1975). In detail, Gregg's patents were used as the footing of the LaserDisc specification that was co-developed between MCA and Philips subsequently MCA purchased Gregg's patents, as well as the company he founded, Gauss Electrophysics.^[3] The LaserDisc was the immediate precursor to the CD, with the primary difference being that the LaserDisc encoded information through an analog procedure whereas the CD used digital encoding.

Central work to digitize the optical disc was performed by Toshi Doi and Kees Schouhamer Immink during 1979–1980, who worked on a taskforce for Sony and Phillips.^[4] The outcome was the Compact Disc Digital Audio (CD-DA), defined on 1980. The CD-ROM was later designed an extension of the CD-DA, and adjusted this format to agree any form of digital data, with an initial storage capacity of 553 MB.^[5] Sony and Philips created the technical standard that defines the format of a CD-ROM in 1983,^[6] in what came to exist chosen the Yellow Book. The CD-ROM was announced in 1984^[7] and introduced by Denon and Sony at the showtime Japanese COMDEX computer evidence in 1985.^[8] In November, 1985, several figurer manufacture participants including Microsoft, Philips, Sony, Apple tree and Digital Equipment Corporation met to create a specification to define a file system format for CD-ROMs.^[9] The resulting specification, called the High Sierra format, was published in May 1986.^[ix] It was somewhen standardized, with a few changes, every bit the ISO 9660 standard in 1988. One of the start CD-ROM products to be made bachelor to the public was the Grolier Academic Encyclopedia, presented at the Microsoft CD-ROM Conference in March 1986.^[9]

CD-ROMs began beingness used in dwelling video game consoles starting with the PC Engine CD-ROM² (TurboGrafx-CD) in 1988, while CD-ROM drives had also become available for home computers by the terminate of the 1980s. In 1990, Data East demonstrated an arcade system board that supported CD-ROMs, like to 1980s laserdisc video games but with digital data, allowing more flexibility than older laserdisc games.^[10] By early 1990, about 300,000 CD-ROM drives were sold in Japan, while 125,000 CD-ROM discs were being produced monthly in the Us.^[11] Some computers which were marketed in the 1990s were called "multimedia" computers because they incorporated a CD-ROM bulldoze, which allowed for the delivery of several hundred megabytes of video, picture, and audio data.

CD-ROM discs [edit]

Media [edit]

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

CD-ROMs are identical in appearance to sound CDs, and data are stored and retrieved in a very similar manner (only differing from sound CDs in the standards used to shop the data). Discs are fabricated from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminium to make a reflective surface. The most mutual size of CD-ROM is 120 mm in diameter, though the smaller Mini CD standard with an 80 mm bore, too equally shaped compact discs in numerous not-standard sizes and molds (due east.m., business organization carte du jour-sized media), likewise exist.

Data is stored on the disc as a series of microscopic indentations called "pits", with the non-indented spaces between them called "lands". A light amplification by stimulated emission of radiation is shone onto the reflective surface of the disc to read the blueprint of pits and lands. Because the depth of the pits is approximately one-quarter to one-sixth of the wavelength of the laser lite used to read the disc, the reflected beam'southward phase is shifted in relation to the incoming axle, causing destructive interference and reducing the reflected beam's intensity. This is converted into binary information.

Standard [edit]

Several formats are used for data stored on compact discs, known as the Rainbow Books. The Yellow Volume, created in 1983,^[6] ^[12] defines the specifications for CD-ROMs, standardized in 1988 as the ISO/IEC 10149^[1] standard and in 1989 equally the ECMA-130^[thirteen] standard. The CD-ROM standard builds on summit of the original Cherry Book CD-DA standard for CD audio. Other standards, such equally the White Book for Video CDs, farther define formats based on the CD-ROM specifications. The Yellowish Book itself is not freely available, simply the standards with the corresponding content tin exist downloaded for costless from ISO or ECMA.

There are several standards that ascertain how to structure data files on a CD-ROM. 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-in one case and re-writeable discs such as CD-R and CD-RW, too as multiple sessions. The ISO 13346 standard was designed to address near of the shortcomings of ISO 9660,^[14] and a subset of it evolved into the UDF format, which was adopted for DVDs. A bootable CD specification, called El Torito, was issued in January 1995, to make a CD emulate a hard disk drive or floppy disk.

Industry [edit]

Pre-pressed CD-ROMs are mass-produced by a process of stamping where a glass master disc is created and used to brand "stampers", which are in plow used to manufacture multiple copies of the final disc with the pits already nowadays. Recordable (CD-R) and rewritable (CD-RW) discs are manufactured by a unlike method, whereby the data are recorded on them by a light amplification by stimulated emission of radiation changing the backdrop of a dye or stage transition material in a process that is oftentimes referred to as "burning".

CD-ROM format [edit]

Data stored on CD-ROMs follows the standard CD information encoding techniques described in the Red Book specification (originally defined for sound CD merely). This includes cross-interleaved Reed–Solomon coding (CIRC), eight-to-fourteen modulation (EFM), and the use of pits and lands for coding the $.25 into the physical surface of the CD.

The structures used to grouping information on a CD-ROM are also derived from the Red Book. Like audio CDs (CD-DA), a CD-ROM sector contains ii,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 sound samples encoded according to the audio CD specification. To structure, address and protect this data, the CD-ROM standard farther defines two sector modes, Mode 1 and Fashion two, which describe two different layouts for the data inside a sector.^[ii] A track (a group of sectors) within a CD-ROM simply contains sectors in the aforementioned manner, but if multiple tracks are present in a CD-ROM, each rail can have its sectors in a different mode from the residue of the tracks. They can also coexist with audio CD tracks, which is the case of mixed way CDs.

Sector construction [edit]

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. Different an audio CD, a CD-ROM cannot rely on error darkening by interpolation; a college reliability of the retrieved data is required. To achieve improved error correction and detection, Style ane, used mostly for digital data, adds a 32-chip cyclic redundancy check (CRC) code for mistake detection, and a tertiary layer of Reed–Solomon mistake correction^{[n 1]} using a Reed-Solomon Product-like Code (RSPC). Mode 1 therefore contains 288 bytes per sector for fault detection and correction, leaving two,048 bytes per sector available for data. Mode two, which is more appropriate for image or video information (where perfect reliability may be a little chip less important), contains no additional error detection or correction bytes, having therefore 2,336 available data bytes per sector. Notation that both modes, similar audio CDs, however do good from the lower layers of error correction at the frame level.^[15]

Before being stored on a disc with the techniques described above, each CD-ROM sector is scrambled to prevent some problematic patterns from showing up.^[13] These scrambled sectors so follow the same encoding procedure described in the Cherry 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:^[13]

Format	← 2,352 byte sector structure →
CD digital audio:	ii,352 (Digital sound)
CD-ROM Mode 1:	12 (Sync pattern)	3 (Address)	1 (Mode, 0x01)	2,048 (Data)	4 (Error detection)	8 (Reserved, cipher)	276 (Fault correction)
CD-ROM Manner 2:	12 (Sync blueprint)	iii (Accost)	1 (Style, 0x02)	ii,336 (Data)

The net byte rate of a Manner-1 CD-ROM, based on comparison to CD-DA audio standards, is 44,100 Hz × 16 $.25/sample × two channels × 2,048 / two,352 / eight = 150 KB/s (150 × 2^ten) . This value, 150 Kbyte/due south, is defined as "1× speed". Therefore, for Mode ane CD-ROMs, a 1× CD-ROM drive reads 150/2 = 75 consecutive sectors per second.

The playing fourth dimension of a standard CD is 74 minutes, or iv,440 seconds, independent in 333,000 blocks or sectors. Therefore, the internet capacity of a Manner-1 CD-ROM is 650 MB (650 × two^xx). For 80 minute CDs, the capacity is 703 MB.

CD-ROM XA extension [edit]

CD-ROM XA is an extension of the Yellow Volume standard for CD-ROMs that combines compressed audio, video and computer data, allowing all to exist accessed simultaneously.^[16] It was intended equally a bridge between CD-ROM and CD-i (Light-green Book) and was published by Sony and Philips, and backed by Microsoft, in 1991,^[17] first announced in September 1988.^[xviii] "XA" stands for eXtended Architecture.

CD-ROM XA defines two new sector layouts, chosen Fashion two Class 1 and Mode 2 Form two (which are different from the original Mode ii). XA Mode two Grade 1 is like to the Mode 1 structure described above, and tin interleave with XA Manner ii Grade ii sectors; it is used for information. XA Mode 2 Form two has 2,324 bytes of user data, and is similar to the standard Mode two but with error detection bytes added (though no mistake correction). It tin can interleave with XA Style 2 Grade 1 sectors, and it is used for audio/video data.^[xv] Video CDs, Super Video CDs, Photo CDs, Enhanced Music CDs and CD-i use these sector modes.^[19]

The post-obit table shows a comparison of the construction of sectors in CD-ROM XA modes:

Format	← 2,352 byte sector structure →
CD-ROM XA Mode 2, Grade ane:	12 (Sync design)	3 (Address)	1 (Manner)	eight (Subheader)	2,048 (Information)	4 (Fault detection)	276 (Error correction)
CD-ROM XA Mode 2, Form ii:	12 (Sync pattern)	3 (Address)	one (Way)	viii (Subheader)	2,324 (Data)			4 (Error detection)

Disc images [edit]

When a disc paradigm of a 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'south useful data (ii,048/two,336/two,352/2,324 bytes depending on the CD-ROM mode). The file size of a disc image created in raw manner is e'er a multiple of ii,352 bytes (the size of a block).^[20] Disc paradigm formats that store raw 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 manner 1 image is created by extracting only each sector'due south 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 way, up to 333,000 × two,352 = 783,216,000 bytes (~747 MB). This is the upper limit for raw images created on a 74 min or ≈650 MB Red Book CD. The fourteen.8% increase is due to the discarding of mistake correction data.

Chapters [edit]

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

CD-ROM capacities are commonly expressed with binary prefixes, subtracting the space used for error correction data. The capacity of a CD-ROM depends on how shut the outward data track is extended to the disc'due south outer rim.^[21] A standard 120 mm, 700 MB CD-ROM tin can actually concur about 703 MB of information with error correction (or 847 MB full). In comparison, a unmarried-layer DVD-ROM can hold iv.7 GB (4.7 × 10⁹) of error-protected information, more than 6 CD-ROMs.

Capacities of Meaty Disc types (xc and 99 infinitesimal discs are not standard)
Type	Sectors	Data (mode 1) max. size		Audio max. size	Fourth dimension
Type	Sectors	(MB)	Approx. (1 = 2²⁰)	(MB)	(min)
8 cm	94,500	193.536	184.570	222.264	21
553 MB	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	fourscore
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; (1 = two²⁰) values are judge.

CD-ROM drives [edit]

This section needs expansion with: Data on admission time latency. You can help past adding to it. (June 2014)

A view of a CD-ROM bulldoze'due south disassembled laser arrangement

The movement of the light amplification by stimulated emission of radiation enables reading at any position of the CD

The laser organization of a CD-ROM drive

CD-ROM discs are read using CD-ROM drives. A CD-ROM bulldoze 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 and Mitsumi standards. Virtually all modern CD-ROM drives can also play sound CDs (as well as Video CDs and other data standards) when used with the right software.

Laser and eyes [edit]

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

Transfer rates [edit]

Original speed [edit]

CD-ROM drives are rated with a speed factor relative to music CDs. If a CD-ROM is read at the aforementioned rotational speed as an sound CD, the data transfer rate is 150 Kbyte/due south, ordinarily called "i×" (with constant linear velocity, curt "CLV"). At this data rate, the rail moves along nether the laser spot at about ane.2 yard/s. To maintain this linear velocity as the optical caput moves to different positions, the angular velocity is varied from near 500 rpm at the inner border to 200 rpm at the outer edge. The 1× speed rating for CD-ROM (150 Kbyte/s) is different from the ane× speed rating for DVDs (1.32 MB/south).

Speed advancements [edit]

Past increasing the speed at which the disc is spun, data tin 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 nine.6 m/s and a transfer rate of 1200 Kbyte/s. Higher up 12× speed virtually drives read at Constant angular velocity (CAV, constant rpm) so that the motor is not made to change from one speed to some other as the head seeks from place to place on the disc. In CAV mode the "×" number denotes the transfer rate at the outer border of the disc, where it is a maximum. 20× was idea to be the maximum speed due to mechanical constraints until Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a brawl bearing system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate usually available is almost 52× or ten,400 rpm and 7.62 MB/due south. Higher spin speeds are limited past the strength of the polycarbonate plastic of which the discs are made. At 52×, the linear velocity of the outermost part of the disc is around 65 thou/south. Notwithstanding, improvements tin can nonetheless be obtained using multiple laser pickups as demonstrated past the Kenwood TrueX 72× which uses vii light amplification by stimulated emission of radiation beams and a rotation speed of approximately 10×.

The first 12× drive was released in late 1996.^[22] Above 12× speed, at that place are problems with vibration and estrus. CAV drives give speeds up to xxx× at the outer edge of the disc with the aforementioned rotational speed as a standard (constant linear velocity, CLV) 12×, or 32× with a slight increase. Nevertheless, 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× boilerplate for a completely full disc, and even less for a partially filled one.

Physical limitations [edit]

Problems with vibration, owing to limits on achievable symmetry and strength in mass-produced media, mean that CD-ROM bulldoze speeds take not massively increased since the late 1990s. Over 10 years later, normally available drives vary betwixt 24× (slimline and portable units, x× spin speed) and 52× (typically CD- and read-only units, 21× spin speed), all using CAV to reach their claimed "max" speeds, with 32× through 48× most common. Even so, these speeds tin crusade poor reading (drive error correction having become very sophisticated in response) and fifty-fifty shattering of poorly made or physically damaged media, with modest cracks rapidly growing into catastrophic breakages when centripetally stressed at 10,000–thirteen,000 rpm (i.e. twoscore–52× CAV). High rotational speeds also produce undesirable racket from disc vibration, rushing air and the spindle motor itself. Most 21st-century drives allow forced low speed modes (past utilise of modest utility programs) for the sake of safety, authentic reading or silence, and will automatically fall dorsum if numerous sequential read errors and retries are encountered.

Workarounds [edit]

Other methods of improving read speed were trialled such as using multiple optical beams, increasing throughput up to 72× with a ten× spin speed, but along with other technologies like xc~99 minute recordable media, GigaRec and double-density compact disc (Purple Book standard) recorders, their utility was nullified past the introduction of consumer DVD-ROM drives capable of consistent 36× equivalent CD-ROM speeds (iv× DVD) or college. Additionally, with a 700 MB CD-ROM fully readable in nether 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 upward/down and random seek times, making for much decreased returns on development investment. A similar stratification result has since been seen in DVD development where maximum speed has stabilised at 16× CAV (with infrequent cases between 18× and 22×) and chapters at 4.iii and eight.5 GB (single and dual layer), with college speed and chapters needs instead being catered to by Blu-ray drives.

Speed ratings [edit]

CD-Recordable drives are often sold with three different speed ratings, i speed for write-one time operations, ane for re-write operations, and one for read-but operations. The speeds are typically listed in that order; i.due east. a 12×/10×/32× CD drive can, CPU and media permitting, write to CD-R discs at 12× speed (1.76 MB/due south), write to CD-RW discs at 10× speed (1.46 MB/s), and read from CDs at 32× speed (4.69 MB/s).

Speed table [edit]

Common data transfer speeds for CD-ROM drives
Transfer speed	KB/s	Mbit/southward	MB/s ^{[n two]}	RPM (outer to inner edge)
ane×	150	one.2288	0.146	200–530^[23] ^[24]
ii×	300	ii.4576	0.293	400–i,060
4×	600	4.9152	0.586	800–2,120
eight×	1,200	9.8304	1.17	1,600–four,240
10×	i,500	12.288	1.46	2,000–5,300
12×	1,800	14.7456	one.76	ii,400–6,360
20×	i,200–three,000	up to 24.576	upwardly to ii.93	4,000 (CAV)
24×	ane,440–3,600	up to 29.491	up to three.51	4,800 (CAV)
32×	1,920–4,800	upwards to 39.3216	up to 4.69	half dozen,400 (CAV)
36×	ii,160–5,400	up to 44.2368	upwardly to 5.27	vii,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	upwardly to 7.03	9,600 (CAV)
52×	iii,120–7,800	up to 63.8976	up to 7.62	x,400 (CAV)
56×	3,360–eight,400	upward to 68.8128	up to eight.20	11,200 (CAV)^[25]
72×	half-dozen,750–x,800	upward to 88.4736	upwards to 10.5	2,700 (multi-axle)^[26] ^[27]

Copyright issues [edit]

Software distributors, and in particular distributors of figurer games, often make use of various copy protection schemes to prevent software running from whatsoever 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 hard 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 estimator's CD-ROM drive.^{[ citation needed ]}

Manufacturers of CD writers (CD-R or CD-RW) are encouraged past 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.^[28] This is a analogue to the Source Identification Code (SID), an eight character code first with "IFPI" that is commonly stamped on discs produced by CD recording plants.

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]

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^ What are CD-ROM Style-ane, Mode-two and XA? Archived 2013-01-26 at the Wayback Machine, Sony Storage Support
^ "What is Yellowish Book?". Searchstorage.techtarget.com. Archived from the original on 2018-x-17. Retrieved 2013-09-23 .
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^ "Optical Media FAQs" (PDF). Archived from the original (PDF) on 2006-10-22. Retrieved 2007-01-06 .
^ Halfhill, Tom R. (October 1996). "CDs for the Gigabyte Era". Retrieved 2022-02-11 .
^ "Gadget". Next Generation. No. 25. Imagine Media. January 1997. p. thirty. Hither comes Diamond with the first 12X CD-ROM.
^ "1x CD-ROM". encyclopedia2.thefreedictionary.com.
^ Computer Architecture and Organization Design Principles and Applications. Tata McGraw-Colina. 2004. p. 547. ISBN978-0070532366.
^ "CD-Recordable FAQ - department 5". cdrfaq.org.
^ "Kenwood's 72X CD can't go along step with 24X CD-RW". GCN. August 7, 2000.
^ "Kenwood Technologies Releases Kenwood 72x TrueX CD-ROM Bulldoze". www.infotoday.com.
^ Schoen, Seth (2007-06-20). "Harry Potter and the Digital Fingerprints". Electronic Borderland Foundation. Archived from the original on 2017-11-07. Retrieved Oct 24, 2007.