
An optical disc is a flat, usually disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid of a beam of light. Optical discs can be reflective, where the light source and detector are on the same side of the disc, or transmissive, where light shines through the disc to be detected on the other side.


Optical discs can store analog information (e.g. Laserdisc), digital information (e.g. DVD), or store both on the same disc (e.g. CD Video).
Their main uses are the distribution of media and data, and long-term archival.
Design and technology
The encoding material sits atop a thicker substrate (usually polycarbonate) that makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track.
The data are stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive that spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (outer tracks are read at a higher data speed due to higher linear velocities at the same angular velocities).
Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by their grooves. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer.
The reverse side of an optical disc usually has a printed label, sometimes made of paper but often printed or stamped onto the disc itself. Unlike the 31⁄2-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems. Blu-rays have a coating called durabis that mitigates these problems.
Optical discs are usually between 7.6 and 30 cm (3.0 and 11.8 in) in diameter, with 12 cm (4.7 in) being the most common size. The so-called program area that contains the data commonly starts 25 millimetres away from the center point. A typical disc is about 1.2 mm (0.047 in) thick, while the track pitch (distance from the center of one track to the center of the next) ranges from 1.6 μm (for CDs) to 320 nm (for Blu-ray discs).
Recording types
An optical disc is designed to support one of three recording types: read-only (such as CD and CD-ROM), recordable (write-once, like CD-R), or re-recordable (rewritable, like CD-RW). Write-once optical discs commonly have an organic dye (may also be a (phthalocyanine) azo dye, mainly used by Verbatim, or an oxonol dye, used by Fujifilm) recording layer between the substrate and the reflective layer. Rewritable discs typically contain an alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony, and tellurium. Azo dyes were introduced in 1996 and phthalocyanine only began to see wide use in 2002. The type of dye and the material used on the reflective layer on an optical disc may be determined by shining a light through the disc, as different dye and material combinations have different colors.
Blu-ray Disc recordable discs do not usually use an organic dye recording layer, instead using an inorganic recording layer. Those that do are known as low-to-high (LTH) discs and can be made in existing CD and DVD production lines, but are of lower quality than traditional Blu-ray recordable discs.
File systems
File systems specifically created for optical discs are ISO9660 and the Universal Disk Format (UDF).
ISO9660 can be extended using the "Joliet" extension to store longer file names than standalone ISO9660. The "Rock Ridge" extension can store even longer file names and Unix/Linux-style file permissions, but is not recognized by Windows and by DVD players and similar devices that can read data discs.
For cross-platform compatibility, multiple file systems can co-exist on one disc and reference the same files.
Usage
Optical discs are most commonly used for digital preservation, storing music (particularly for use in a CD player), video (such as for use in a Blu-ray player), or data and programs for personal computers (PC), as well as offline hard copy data distribution due to lower per-unit prices than other types of media. The Optical Storage Technology Association (OSTA) promoted standardized optical storage formats.
Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer's optical disc drive or corresponding disc player.
File operations of traditional mass storage devices such as flash drives, memory cards and hard drives can be simulated using a UDF live file system.
For computer data backup and physical data transfer, optical discs such as CDs and DVDs are gradually being replaced with faster, smaller solid-state devices, especially the USB flash drive. This trend is expected to continue as USB flash drives continue to increase in capacity and drop in price.[citation needed]
Additionally, music, movies, games, software and TV shows purchased, shared or streamed over the Internet has significantly reduced the number of audio CDs, video DVDs and Blu-ray discs sold annually. However, audio CDs and Blu-rays are still preferred and bought by some, as a way of supporting their favorite works while getting something tangible in return and also since audio CDs (alongside vinyl records and cassette tapes) contain uncompressed audio without the artifacts introduced by lossy compression algorithms like MP3, and Blu-rays offer better image and sound quality than streaming media, without visible compression artifacts, due to higher bitrates and more available storage space. However, Blu-rays may sometimes be torrented over the internet, but torrenting may not be an option for some, due to restrictions put in place by ISPs on legal or copyright grounds, low download speeds or not having enough available storage space, since the content may weigh up to several dozen gigabytes. Blu-rays may be the only option for those looking to play large games without having to download them over an unreliable or slow internet connection, which is the reason why they are still (as of 2020) widely used by gaming consoles, like the PlayStation 4 and Xbox One X. As of 2020, it is unusual for PC games to be available in a physical format like Blu-ray.
Optical discs are typically stored in special cases, sometimes called jewel cases. Discs should not have any stickers and should not be stored together with paper; papers must be removed from the jewel case before storage. Discs should be handled by the edges to prevent scratching, with the thumb on the inner edge of the disc. The ISO Standard 18938:2014 is about best optical disc handling techniques. Optical disc cleaning should never be done in a circular pattern, to avoid concentric cirles from forming on the disc. Improper cleaning can scratch the disc. Recordable discs should not be exposed to light for extended periods of time. Optical discs should be stored in dry and cool conditions to increase longevity, with temperatures between -10 and 23 °C, never exceeding 32 °C, and with humidity never falling below 10%, with recommended storage at 20 to 50% of humidity without fluctuations of more than ±10%.
Durability
Although optical discs are more durable than earlier audio-visual and data storage formats, they are susceptible to environmental and daily-use damage, if handled improperly.
Optical discs are not prone to uncontrollable catastrophic failures such as head crashes, power surges, or exposure to water like hard disk drives and flash storage, since optical drives' storage controllers are not tied to optical discs themselves like with hard disk drives and flash memory controllers, and a disc is usually recoverable from a defective optical drive by pushing an unsharp needle into the emergency ejection pinhole, and has no point of immediate water ingress and no integrated circuitry.
Security
As the media itself only is accessed through a laser beam and has no internal control circuitry, it cannot contain malicious hardware in the same way as so-called rubber-duckies or USB killers. Like any data storage media, optical discs can contain malicious data, they are able to contain and spread malware - as happened in the case of the Sony BMG copy protection rootkit scandal in 2005 where Sony misused discs by pre-loading them with malware.
Many types of optical discs are factory-pressed or finalized write once read many storage devices and would therefore not be effective at spreading computer worms that are designed to spread by copying themselves onto optical media, because data on those discs can not be modified once pressed or written. However, re-writable disc technologies (such as CD-RW) are able to spread this type of malware.
History
This article possibly contains original research.(July 2009) |
The first recorded historical use of an optical disc was in 1884 when Alexander Graham Bell, Chichester Bell and Charles Sumner Tainter recorded sound on a glass disc using a beam of light.
Optophonie is a very early (1931) example of a recording device using light for both recording and playing back sound signals on a transparent photograph.
An early analogue optical disc system existed in 1935, used on Welte's
sampling organ.An early analog optical disc used for video recording was invented by David Paul Gregg in 1958 and patented in the US in 1961 and 1969. This form of optical disc was a very early form of the DVD (U.S. patent 3,430,966). It is of special interest that U.S. patent 4,893,297, filed 1989, issued 1990, generated royalty income for Pioneer Corporation's DVA until 2007 —then encompassing the CD, DVD, and Blu-ray systems. In the early 1960s, the Music Corporation of America bought Gregg's patents and his company, Gauss Electrophysics.
American inventor James T. Russell has been credited with inventing the first system to record a digital signal on an optical transparent foil that is lit from behind by a high-power halogen lamp. Russell's patent application was first filed in 1966 and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's patents (then held by a Canadian company, Optical Recording Corp.) in the 1980s.
Both Gregg's and Russell's disc are floppy media read in transparent mode, which imposes serious drawbacks, after this were developed four generations of optical drive that includes Laserdisc (1969), WORM (1979), Compact Discs (1984), DVD (1995), Blu-ray (2005), HD-DVD (2006), more formats are currently under development.
First-generation
From the start optical discs were used to store broadcast-quality analog video, and later digital media such as music or computer software. The LaserDisc format stored analog video signals for the distribution of home video, but commercially lost to the VHS videocassette format, due mainly to its high cost and non-re-recordability; other first-generation disc formats were designed only to store digital data and were not initially capable of use as a digital video medium.
Most first-generation disc devices had an infrared laser reading head. The minimum size of the laser spot is proportional to the wavelength of the laser, so wavelength is a limiting factor upon the amount of information that can be stored in a given physical area on the disc. The infrared range is beyond the long-wavelength end of the visible light spectrum, so it supports less density than shorter-wavelength visible light. One example of high-density data storage capacity, achieved with an infrared laser, is 700 MB of net user data for a 12 cm compact disc.
Other factors that affect data storage density include: the existence of multiple layers of data on the disc, the method of rotation (Constant linear velocity (CLV), Constant angular velocity (CAV), or zoned-CAV), the composition of lands and pits, and how much margin is unused is at the center and the edge of the disc.
Types of Optical Discs:
- Compact disc (CD) and derivatives
- Audio CD
- Video CD (VCD)
- Super Video CD
- CD Video
- CD-Interactive
- LaserDisc
- GD-ROM
- Phase-change Dual
- Double Density Compact Disc (DDCD)
- Magneto-optical disc
- MiniDisc (MD)
- MD Data
- Write Once Read Many (WORM)
Laserdisc
In the Netherlands in 1969, Philips Research physicist, Pieter Kramer invented an optical videodisc in reflective mode with a protective layer read by a focused laser beam U.S. patent 5,068,846, filed 1972, issued 1991. Kramer's physical format is used in all optical discs.
In 1975, Philips and MCA began to work together, and in 1978, commercially much too late, they presented their long-awaited Laserdisc in Atlanta. MCA delivered the discs and Philips the players. However, the presentation was a commercial failure, and the cooperation ended.
In Japan and the U.S., Pioneer succeeded with the Laserdisc until the advent of the DVD. In 1979, Philips and Sony, in consortium, successfully developed the audio compact disc.
WORM drive
In 1979, Exxon STAR Systems in Pasadena, CA built a computer controlled WORM drive that utilized thin film coatings of Tellurium and Selenium on a 12" diameter glass disk. The recording system utilized blue light at 457 nm to record and red light at 632.8 nm to read. STAR Systems was bought by Storage Technology Corporation (STC) in 1981 and moved to Boulder, CO. Development of the WORM technology was continued using 14" diameter aluminum substrates. Beta testing of the disk drives, originally labeled the Laser Storage Drive 2000 (LSD-2000), was only moderately successful. Many of the disks were shipped to RCA Laboratories (now David Sarnoff Research Center) to be used in the Library of Congress archiving efforts. The STC disks utilized a sealed cartridge with an optical window for protection U.S. patent 4,542,495.
CD-ROM
The CD-ROM format was developed by Sony and Philips, introduced in 1984, as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data. The same year, Sony demonstrated a LaserDisc data storage format, with a larger data capacity of 3.28 GB.
In the late 1980s and early 1990s, Optex, Inc. of Rockville, MD, built an erasable optical digital video disc system U.S. patent 5,113,387 using Electron Trapping Optical Media (ETOM)U.S. patent 5,128,849. Although this technology was written up in Video Pro Magazine's December 1994 issue promising "the death of the tape", it was never marketed.
Magnetic disks found limited applications in storing the data in large amount. So, there was the need of finding some more data storing techniques. As a result, it was found that by using optical means large data storing devices can be made that in turn gave rise to the optical discs. The very first application of this kind was the compact disc (CD), which was used in audio systems.
Sony and Philips developed the first generation of the CDs in the mid-1980s with the complete specifications for these devices. With the help of this kind of technology the possibility of representing the analog signal into digital signal was exploited to a great level. For this purpose, the 16-bit samples of the analog signal were taken at the rate of 44,100 samples per second. This sample rate was based on the Nyquist rate of 40,000 samples per second required to capture the audible frequency range to 20 kHz without aliasing, with an additional tolerance to allow the use of less-than-perfect analog audio pre-filters to remove any higher frequencies. The first version of the standard allowed up to 74 minutes of music or 650 MB of data storage.
Second-generation
Second-generation optical discs were for storing great amounts of data, including broadcast-quality digital video. Such discs usually are read with a visible-light laser (usually red); the shorter wavelength and greater numerical aperture allow a narrower light beam, permitting smaller pits and lands in the disc. In the DVD format, this allows 4.7 GB storage on a standard 12 cm, single-sided, single-layer disc; alternatively, smaller media, such as the DataPlay format, can have capacity comparable to that of the larger, standard compact 12 cm disc.
- DVD and derivatives
- DVD-Audio
- DualDisc
- Digital Video Express (DIVX)
- DVD-RAM
- DVD±R
- Nintendo GameCube Game Disc (miniDVD derivative)
- Wii Optical Disc (DVD derivative)
- Super Audio CD (SACD)
- Enhanced Versatile Disc
- DataPlay
- Hi-MD
- Universal Media Disc (UMD)
- Ultra Density Optical
DVD-ROM
In 1995, a consortium of manufacturers (Sony, Philips, Toshiba, Panasonic) developed the second generation of the optical disc, the DVD. The DVD disc appeared after the CD-ROM had become widespread in society.
Third-generation
Third-generation optical discs are used for distributing high-definition video and videogames and support greater data storage capacities, accomplished with short-wavelength visible-light lasers and greater numerical apertures. Blu-ray Disc and HD DVD uses blue-violet lasers and focusing optics of greater aperture, for use with discs with smaller pits and lands, thereby greater data storage capacity per layer. In practice, the effective multimedia presentation capacity is improved with enhanced video data compression codecs such as H.264/MPEG-4 AVC and VC-1.
- Blu-ray and derivatives (up to 400 GB - experimental)
- BD-R and BD-RE
- High Fidelity Pure Audio
- AVCHD and AVCREC
- BDXL and Blu-ray 3D
- 4K Blu-ray and 8K Blu-ray
- Wii U Optical Disc (25 GB per layer)
- HD DVD (discontinued disc format, up to 51 GB triple layer)
- CBHD (a derivative of the HD DVD format)
- HD VMD
- Professional Disc
Announced but not released:
- Digital Multilayer Disk
- Fluorescent Multilayer Disc
- Forward Versatile Disc
Blu-ray and HD-DVD
The third generation optical disc was developed in 2000–2006 and was introduced as Blu-ray Disc. First movies on Blu-ray Discs were released in June 2006. Blu-ray eventually prevailed in a high definition optical disc format war over a competing format, the HD DVD. A standard Blu-ray disc can hold about 25 GB of data, a DVD about 4.7 GB, and a CD about 700 MB.
Fourth-generation
The following formats go beyond the current third-generation discs and have the potential to hold more than one terabyte (1 TB) of data and at least some are meant for cold data storage in data centers:[dubious – discuss]
- Archival Disc
- Holographic Versatile Disc
Announced but not released:
- LS-R
- Protein-coated disc
- Stacked Volumetric Optical Disc
- 5D DVD
- 3D optical data storage (not a single technology, examples are Hyper CD-ROM and Fluorescent Multilayer Disc)
In 2004, development of the Holographic Versatile Disc (HVD) commenced, which promised the storage of several terabytes of data per disc. However, development stagnated towards the late 2000s due to lack of funding.
In 2006, it was reported that Japanese researchers developed ultraviolet ray lasers with a wavelength of 210 nanometers, which would enable a higher bit density than Blu-ray discs. As of 2022, no updates on that project have been reported.
Overview of optical types
Name | Capacity | Experimental | Years |
---|---|---|---|
LaserDisc (LD) | N/A | 1971–2007 | |
Write Once Read Many Disk (WORM) | 0.2–6.0 GB | 1979–1984 | |
Compact disc (CD) | 0.7–0.9 GB | 1982–present | |
Electron Trapping Optical Memory (ETOM) | 6.0–12.0 GB | 1987–1996 | |
MiniDisc (MD) | 0.14–1.0 GB | 1989–2025 | |
Magneto Optical Disc (MOD) | 0.1–16.7 GB | 1990–present | |
Digital Versatile Disc (DVD) | 4.7–17 GB | 1995–present | |
LIMDOW (Laser Intensity Modulation Direct OverWrite) | 2.6 GB | 10 GB | 1996–present |
GD-ROM | 1.2 GB | 1997–2006 | |
Fluorescent Multilayer Disc | 50–140 GB | 1998-2003 | |
Versatile Multilayer Disc (VMD) | 5–20 GB | 100 GB | 1999-2010 |
Hyper CD-ROM | 1 PB | 100 EB | 1999–present |
DataPlay | 500 MB | 1999-2006 | |
Ultra Density Optical (UDO) | 30–60 GB | 2000–present | |
Forward Versatile Disc (FVD) | 5.4–15 GB | 2005–2006 | |
Enhanced Versatile Disc (EVD) | DVD | 2002-2004 | |
HD DVD | 15–51 GB | 1 TB[citation needed] | 2002-2008 |
Blu-ray Disc (BD) | 25 GB 50 GB | 2002–present | |
BDXL | 100 GB, 128 GB | 1 TB | 2010–present |
Professional Disc for Data (PDD) | 23 GB | 2003-2006 | |
Professional Disc | 23–128 GB | 2003–present | |
Digital Multilayer Disk | 22-32 GB | 2004–2007 | |
Multiplexed Optical Data Storage (MODS-Disc) | 250 GB–1 TB | 2004–present | |
Universal Media Disc (UMD) | 0.9–1.8 GB | 2004–2014 | |
Holographic Versatile Disc (HVD) | 6.0 TB | 2004–2012 | |
Protein-coated disc (PCD) | 50 TB | 2005–2006 | |
M-DISC | 4.7 GB (DVD format) 25 GB (Blu-ray format) 50 GB (Blu-ray format) 100 GB (BDXL format) | 2009–present | |
Archival Disc | 0.3-1 TB | 2014–present | |
Ultra HD Blu-ray | 50 GB 66 GB 100 GB 128 GB | 2015–present |
- Notes
- Prototypes and theoretical values.
- Years from (known) start of development till end of sales or development.
Recordable and writable optical discs
There are numerous formats of optical direct to disk recording devices on the market, all of which are based on using a laser to change the reflectivity of the digital recording medium in order to duplicate the effects of the pits and lands created when a commercial optical disc is pressed. Formats such as CD-R and DVD-R are "Write once read many" or write-once, while CD-RW and DVD-RW are rewritable, more like a magnetic recording hard disk drive (HDD).
Media technologies vary, for example, M-DISC media uses a rock-like layer to retain data for longer than conventional recordable media. While being read-only compatible with existing DVD and Blu-ray drives, M-DISC media can only be written to using a stronger laser specifically made for this purpose, which is built into fewer optical drive models.
Surface error scanning
This section needs expansion. You can help by adding to it. (July 2020) |
Optical media can predictively be scanned for errors and media deterioration well before any data becomes unreadable. Optical formats include some redundancy for error correction, which works until the amount of error exceeds a threshold. A higher rate of errors may indicate deteriorating and/or low quality media, physical damage, an unclean surface and/or media written using a defective optical drive.
Precise error scanning requires access to the raw, uncorrected readout of a disc, which is not always provided by a drive. As a result, support of this functionality varies per optical drive manufacturer and model. On ordinary drives without this functionality, it is possible to still look for unexpected reduction in read speed as an indirect, much less reliable measure.
Optical media, such as CDs and DVDs, can be scanned to detect errors and signs of deterioration well before data becomes unreadable. These formats include built-in error correction mechanisms, which function by adding redundant data. However, once the rate of errors surpasses the correction threshold, the media becomes vulnerable to failure. A high error rate can signal physical deterioration, low-quality manufacturing, surface contamination, or data recorded by a faulty optical drive.
Accurate error scanning requires access to a disc's raw, uncorrected readout. However, not all optical drives provide this capability, and support for this feature can vary significantly between manufacturers and drive models. On drives lacking raw data access, users may rely on a less precise method: monitoring unexpected reductions in read speed, though this is a far less reliable indicator of disc health.
Several specialized tools are available for performing error scans on optical media. Popular programs include Nero DiscSpeed, K-Probe, Opti Drive Control (previously known as "CD Speed 2000"), and DVD Info Pro for Windows. For cross-platform users, QPxTool is available to help monitor and maintain optical media integrity. Each of these tools allows for detailed analysis of the error rates and conditions affecting optical discs.
Error types
There are different types of error measurements, including so-called "C1", "C2" and "CU" errors on CDs, and "PI/PO (parity inner/outer) errors" and the more critical "PI/PO failures" on DVDs. Finer-grain error measurements on CDs supported by very few optical drives are called E11, E21, E31, E21, E22, E32.
"CU" and "POF" represent uncorrectable errors on data CDs and DVDs respectively, thus data loss, and can be a result of too many consecutive smaller errors.
Due to the weaker error correction used on Audio CDs (Red Book standard) and Video CDs (White Book standard), C2 errors already lead to data loss. However, even with C2 errors, the damage is inaudible to some extent.
Blu-ray discs use so-called LDC (Long Distance Codes) and BIS (Burst Indication Subcodes) error parameters. According to the developer of the Opti Drive Control software, a disc can be considered healthy at an LDC error rate below 13 and BIS error rate below 15.
Optical disc manufacturing
Optical discs are made using replication. This process can be used with all disc types. Recordable discs have pre-recorded vital information, like manufacturer, disc type, maximum read and write speeds, etc. In replication, a cleanroom with yellow light is necessary to protect the light-sensitive photoresist and to prevent dust from corrupting the data on the disc.
A glass master is used in replication. The master is placed in a machine that cleans it as much as possible using a rotating brush and deionized water, preparing it for the next step. In the next step, a surface analyzer inspects the cleanliness of the master before photoresist is applied on the master.
The photoresist is then baked in an oven to solidify it. Then, in the exposure process, the master is placed in a turntable where a laser selectively exposes the resist to light. At the same time, a developer and deionized water are applied to the disc to remove the exposed resist. This process forms the pits and lands that represent the data on the disc.
A thin coating of metal is then applied to the master, making a negative of the master with the pits and lands in it. The negative is then peeled off the master and coated in a thin layer of plastic. The plastic protects the coating while a punching press punches a hole into the center of the disc, and punches excess material.
The negative is now a stamper - a part of the mold that will be used for replication. It is placed on one side of the mold with the data side containing the pits and lands facing out. This is done inside an injection molding machine. The machine then closes the mold and injects polycarbonate in the cavity formed by the walls of the mold, which forms or molds the disc with the data on it.
The molten polycarbonate fills the pits or spaces between the lands on the negative, acquiring their shape when it solidifies. This step is somewhat similar to record pressing.
The polycarbonate disc cools quickly and is promptly removed from the machine, before forming another disc. The disc is then metallized, covered with a thin reflective layer of aluminum. The aluminum fills the space once occupied by the negative.
A layer of varnish is then applied to protect the aluminum coating and provide a surface suitable for printing. The varnish is applied near the center of the disc, and the disc is spun, evenly distributing the varnish on the surface of the disc. The varnish is hardened using UV light. The discs are then silkscreened or a label is otherwise applied.
Recordable discs add a dye layer, and rewritable discs add a phase change alloy layer instead, which is protected by upper and lower dielectric (electrically insulating) layers. The layers may be sputtered. The additional layer is between the grooves and the reflective layer of the disc. Grooves are made in recordable discs in place of the traditional pits and lands found in replicated discs, and the two can be made in the same exposure process. In DVDs, the same processes as in CDs are carried out, but in a thinner disc. The thinner disc is then bonded to a second, equally thin but blank, disc using UV-curable Liquid optically clear adhesive, forming a DVD disc. This leaves the data in the middle of the disc, which is necessary for DVDs to achieve their storage capacity. In multi layer discs, semi reflective instead of reflective coatings are used for all layers except the last layer, which is the deepest one and uses a traditional reflective coating.
Dual layer DVDs are made slightly differently. After metallization (with a thinner metal layer to allow some light to pass through), base and pit transfer resins are applied and pre-cured in the center of the disc. Then the disc is pressed again using a different stamper, and the resins are completely cured using UV light before being separated from the stamper. Then the disc receives another, thicker metallization layer, and is then bonded to the blank disc using LOCA glue. DVD-R DL and DVD+R DL discs receive a dye layer after curing, but before metallization. CD-R, DVD-R, and DVD+R discs receive the dye layer after pressing but before metallization. CD-RW, DVD-RW and DVD+RW receive a metal alloy layer sandwiched between 2 dielectric layers. HD-DVD is made in the same way as DVD. In recordable and rewritable media, most of the stamper is composed of grooves, not pits and lands. The grooves contain a wobble frequency that is used to locate the position of the reading or writing laser on the disc. DVDs use pre-pits instead, with a constant frequency wobble.
Blu-ray
HTL (high-to-low type) Blu-ray discs are made differently. First, a silicon wafer is used instead of a glass master. The wafer is processed in the same way a glass master would.
The wafer is then electroplated to form a 300-micron thick nickel stamper, which is peeled off from the wafer. The stamper is mounted onto a mold inside a press or embosser.
The polycarbonate discs are molded in a similar fashion to DVD and CD discs. If the discs being produced are BD-Rs or BD-REs, the mold is fitted with a stamper that stamps a groove pattern onto the discs, in lieu of the pits and lands found on BD-ROM discs.
After cooling, a 35 nanometre-thick layer of silver alloy is applied to the disc using sputtering. Then the second layer is made by applying base and pit transfer resins to the disc, and are pre-cured in its center.
After application and pre-curing, the disc is pressed or embossed using a stamper and the resins are immediately cured using intense UV light, before the disc is separated from the stamper. The stamper contains the data that will be transferred to the disc. This process is known as embossing and is the step that engraves the data onto the disc, replacing the pressing process used in the first layer, and it is also used for multi layer DVD discs.
Then, a 30 nanometre-thick layer of silver alloy is then sputtered onto the disc and the process is repeated as many times as required. Each repetition creates a new data layer. (The resins are applied again, pre-cured, stamped (with data or grooves) and cured, silver alloy is sputtered and so on)
BD-R and BD-RE discs receive (through sputtering) a metal (recording layer) alloy (that is sandwiched between two dielectric layers, also sputtered, in BD-RE), before receiving the 30 nanometre metallization (silver alloy, aluminum or gold) layer, which is sputtered. Alternatively, the silver alloy may be applied before the recording layer is applied. Silver alloys are usually used in Blu-rays, and aluminum is usually used on CDs and DVDs. Gold is used in some "Archival" CDs and DVDs, since it is more chemically inert and resistant to corrosion than aluminum, which corrodes into aluminum oxide, which can be seen in disc rot as transparent patches or dots in the disc, that prevent the disc from being read, since the laser light passes through the disc instead of being reflected back into the laser pickup assembly to be read. Normally, aluminum does not corrode since it has a thin oxide layer that forms on contact with oxygen. In this case, it can corrode due to its thinness.
Then, the 98 micron-thick cover layer is applied using UV-curable liquid optically clear adhesive, and a 2 micron-thick hard coat (such as Durabis) is also applied and cured using UV light. In the last step, a 10 nanometre-thick silicon nitride barrier layer is applied to the label side of the disc to protect against humidity. Blu-rays have their data very close to the read surface of the disc, which is necessary for Blu-rays to achieve their capacity.
Discs in large quantities can either be replicated or duplicated. In replication, the process explained above is used to make the discs, while in duplication, CD-R, DVD-R or BD-R discs are recorded and finalized to prevent further recording and allow for wider compatibility. (See Optical disc authoring). The equipment is also different: replication is carried out by fully automated purpose-built machinery whose cost is in the hundreds of thousands of US dollars in the used market, while duplication can be automated (using what's known as an autoloader) or be done by hand, and only requires a small tabletop duplicator.
Specifications
Generation | Base | Max | |
---|---|---|---|
(Mbit/s) | (Mbit/s) | × | |
1st (CD) | 1.17 | 65.6 | 56× |
2nd (DVD) | 10.57 | 253.6 | 24× |
3rd (BD) | 36 | 504 | 14× |
4th (AD) | ? | ? | 14× |
Designation | Sides | Layers (total) | Diameter | Capacity | ||
---|---|---|---|---|---|---|
(cm) | (GB) | |||||
BD | SS SL | 1 | 1 | 8 | 7.8 | |
BD | SS DL | 1 | 2 | 8 | 15.6 | |
BD | SS SL | 1 | 1 | 12 | 25 | |
BD | SS DL | 1 | 2 | 12 | 50 | |
BD | SS TL | 1 | 3 | 12 | 100 | |
BD | SS QL | 1 | 4 | 12 | 128 | |
CD–ROM 74 min | SS SL | 1 | 1 | 12 | 0.682 | |
CD–ROM 80 min | SS SL | 1 | 1 | 12 | 0.737 | |
CD–ROM | SS SL | 1 | 1 | 8 | 0.194 | |
DDCD–ROM | SS SL | 1 | 1 | 12 | 1.364 | |
DDCD–ROM | SS SL | 1 | 1 | 8 | 0.387 | |
DVD–1 | SS SL | 1 | 1 | 8 | 1.46 | |
DVD–2 | SS DL | 1 | 2 | 8 | 2.66 | |
DVD–3 | DS SL | 2 | 2 | 8 | 2.92 | |
DVD–4 | DS DL | 2 | 4 | 8 | 5.32 | |
DVD–5 | SS SL | 1 | 1 | 12 | 4.70 | |
DVD–9 | SS DL | 1 | 2 | 12 | 8.54 | |
DVD–10 | DS SL | 2 | 2 | 12 | 9.40 | |
DVD–14 | DS DL/SL | 2 | 3 | 12 | 13.24 | |
DVD–18 | DS DL | 2 | 4 | 12 | 17.08 | |
DVD–R 1.0 | SS SL | 1 | 1 | 12 | 3.95 | |
DVD–R (2.0), +R, –RW, +RW | SS SL | 1 | 1 | 12 | 4.7 | |
DVD-R, +R, –RW, +RW | DS SL | 2 | 2 | 12 | 9.40 | |
DVD–RAM | SS SL | 1 | 1 | 8 | 1.46 | |
DVD–RAM | DS SL | 2 | 2 | 8 | 2.65 | |
DVD–RAM 1.0 | SS SL | 1 | 1 | 12 | 2.58 | |
DVD–RAM 2.0 | SS SL | 1 | 1 | 12 | 4.70 | |
DVD–RAM 1.0 | DS SL | 2 | 2 | 12 | 5.16 | |
DVD–RAM 2.0 | DS SL | 2 | 2 | 12 | 9.40 |
See also
- Disc Description Protocol
- List of optical disc manufacturers
- Universal Disk Format (UDF)
References
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External links
- "Inventor of the Week Archive: The Digital Compact Disc". Massachusetts Institute of Technology. December 1999. Archived from the original on 2008-06-19. Retrieved 2007-07-13.
- Dudley, Brier (November 29, 2004). "Scientist's invention was let go for a song". The Seattle Times. Retrieved 2007-07-13.
- "David Gregg and the Optical Disk". About.com. Archived from the original on 2020-08-19. Retrieved 2007-07-13.
- Byers, Fred R. (2003). Care and Handling of CDs and DVDs — A Guide for Librarians and Archivists (PDF) (Report). National Institute of Standards and Technology. Archived from the original (PDF) on September 23, 2008. Retrieved July 17, 2009.
- Romeyn, Jacob. "50th-anniversary -of-the-optical-disc". Archived from the original on 2015-02-08. Retrieved 2011-06-28.
- "Optical Storage Technology Association".
- O'Kelly, Terence. "Reference Guide for Optical Media" (PDF). Memorex Inc. – via A.N.T. Audio.
- "The history of ideas "the optical disc as a "unique" carrier of information in the systems management". European Society of the History of Science. Archived from the original on 2015-05-18. Retrieved 2013-06-11.
- "Thomson-CSF's transmissive videodisc".
- "Know Your Digital Storage Media: a guide to the most common types of digital storage media found in archives". US: University of Texas at San Antonio.
- Longevity of Recordable CDs, DVDs and Blu-rays — Canadian Conservation Institute (CCI) Notes 19/1
An optical disc is a flat usually disc shaped object that stores information in the form of physical variations on its surface that can be read with the aid of a beam of light Optical discs can be reflective where the light source and detector are on the same side of the disc or transmissive where light shines through the disc to be detected on the other side The bottom surface of a 12 cm compact disc CD R showing characteristic iridescence The optical lens of a compact disc drive Optical discs can store analog information e g Laserdisc digital information e g DVD or store both on the same disc e g CD Video Their main uses are the distribution of media and data and long term archival Design and technologyThe encoding material sits atop a thicker substrate usually polycarbonate that makes up the bulk of the disc and forms a dust defocusing layer The encoding pattern follows a continuous spiral path covering the entire disc surface and extending from the innermost track to the outermost track The data are stored on the disc with a laser or stamping machine and can be accessed when the data path is illuminated with a laser diode in an optical disc drive that spins the disc at speeds of about 200 to 4 000 RPM or more depending on the drive type disc format and the distance of the read head from the center of the disc outer tracks are read at a higher data speed due to higher linear velocities at the same angular velocities Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by their grooves This side of the disc contains the actual data and is typically coated with a transparent material usually lacquer The reverse side of an optical disc usually has a printed label sometimes made of paper but often printed or stamped onto the disc itself Unlike the 31 2 inch floppy disk most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches fingerprints and other environmental problems Blu rays have a coating called durabis that mitigates these problems Optical discs are usually between 7 6 and 30 cm 3 0 and 11 8 in in diameter with 12 cm 4 7 in being the most common size The so called program area that contains the data commonly starts 25 millimetres away from the center point A typical disc is about 1 2 mm 0 047 in thick while the track pitch distance from the center of one track to the center of the next ranges from 1 6 mm for CDs to 320 nm for Blu ray discs Recording types An optical disc is designed to support one of three recording types read only such as CD and CD ROM recordable write once like CD R or re recordable rewritable like CD RW Write once optical discs commonly have an organic dye may also be a phthalocyanine azo dye mainly used by Verbatim or an oxonol dye used by Fujifilm recording layer between the substrate and the reflective layer Rewritable discs typically contain an alloy recording layer composed of a phase change material most often AgInSbTe an alloy of silver indium antimony and tellurium Azo dyes were introduced in 1996 and phthalocyanine only began to see wide use in 2002 The type of dye and the material used on the reflective layer on an optical disc may be determined by shining a light through the disc as different dye and material combinations have different colors Blu ray Disc recordable discs do not usually use an organic dye recording layer instead using an inorganic recording layer Those that do are known as low to high LTH discs and can be made in existing CD and DVD production lines but are of lower quality than traditional Blu ray recordable discs File systems File systems specifically created for optical discs are ISO9660 and the Universal Disk Format UDF ISO9660 can be extended using the Joliet extension to store longer file names than standalone ISO9660 The Rock Ridge extension can store even longer file names and Unix Linux style file permissions but is not recognized by Windows and by DVD players and similar devices that can read data discs For cross platform compatibility multiple file systems can co exist on one disc and reference the same files Usage Optical discs are most commonly used for digital preservation storing music particularly for use in a CD player video such as for use in a Blu ray player or data and programs for personal computers PC as well as offline hard copy data distribution due to lower per unit prices than other types of media The Optical Storage Technology Association OSTA promoted standardized optical storage formats Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer s optical disc drive or corresponding disc player File operations of traditional mass storage devices such as flash drives memory cards and hard drives can be simulated using a UDF live file system For computer data backup and physical data transfer optical discs such as CDs and DVDs are gradually being replaced with faster smaller solid state devices especially the USB flash drive This trend is expected to continue as USB flash drives continue to increase in capacity and drop in price citation needed Additionally music movies games software and TV shows purchased shared or streamed over the Internet has significantly reduced the number of audio CDs video DVDs and Blu ray discs sold annually However audio CDs and Blu rays are still preferred and bought by some as a way of supporting their favorite works while getting something tangible in return and also since audio CDs alongside vinyl records and cassette tapes contain uncompressed audio without the artifacts introduced by lossy compression algorithms like MP3 and Blu rays offer better image and sound quality than streaming media without visible compression artifacts due to higher bitrates and more available storage space However Blu rays may sometimes be torrented over the internet but torrenting may not be an option for some due to restrictions put in place by ISPs on legal or copyright grounds low download speeds or not having enough available storage space since the content may weigh up to several dozen gigabytes Blu rays may be the only option for those looking to play large games without having to download them over an unreliable or slow internet connection which is the reason why they are still as of 2020 widely used by gaming consoles like the PlayStation 4 and Xbox One X As of 2020 it is unusual for PC games to be available in a physical format like Blu ray Optical discs are typically stored in special cases sometimes called jewel cases Discs should not have any stickers and should not be stored together with paper papers must be removed from the jewel case before storage Discs should be handled by the edges to prevent scratching with the thumb on the inner edge of the disc The ISO Standard 18938 2014 is about best optical disc handling techniques Optical disc cleaning should never be done in a circular pattern to avoid concentric cirles from forming on the disc Improper cleaning can scratch the disc Recordable discs should not be exposed to light for extended periods of time Optical discs should be stored in dry and cool conditions to increase longevity with temperatures between 10 and 23 C never exceeding 32 C and with humidity never falling below 10 with recommended storage at 20 to 50 of humidity without fluctuations of more than 10 Durability Optical discs are not vulnerable to water Although optical discs are more durable than earlier audio visual and data storage formats they are susceptible to environmental and daily use damage if handled improperly Optical discs are not prone to uncontrollable catastrophic failures such as head crashes power surges or exposure to water like hard disk drives and flash storage since optical drives storage controllers are not tied to optical discs themselves like with hard disk drives and flash memory controllers and a disc is usually recoverable from a defective optical drive by pushing an unsharp needle into the emergency ejection pinhole and has no point of immediate water ingress and no integrated circuitry Security As the media itself only is accessed through a laser beam and has no internal control circuitry it cannot contain malicious hardware in the same way as so called rubber duckies or USB killers Like any data storage media optical discs can contain malicious data they are able to contain and spread malware as happened in the case of the Sony BMG copy protection rootkit scandal in 2005 where Sony misused discs by pre loading them with malware Many types of optical discs are factory pressed or finalized write once read many storage devices and would therefore not be effective at spreading computer worms that are designed to spread by copying themselves onto optical media because data on those discs can not be modified once pressed or written However re writable disc technologies such as CD RW are able to spread this type of malware HistoryAn earlier analog optical disc recorded in 1935 for de sampling organ Lichttonorgel amp optical disc system This article possibly contains original research Please improve it by verifying the claims made and adding inline citations Statements consisting only of original research should be removed July 2009 Learn how and when to remove this message The first recorded historical use of an optical disc was in 1884 when Alexander Graham Bell Chichester Bell and Charles Sumner Tainter recorded sound on a glass disc using a beam of light Optophonie is a very early 1931 example of a recording device using light for both recording and playing back sound signals on a transparent photograph An early analogue optical disc system existed in 1935 used on Welte s de sampling organ An early analog optical disc used for video recording was invented by David Paul Gregg in 1958 and patented in the US in 1961 and 1969 This form of optical disc was a very early form of the DVD U S patent 3 430 966 It is of special interest that U S patent 4 893 297 filed 1989 issued 1990 generated royalty income for Pioneer Corporation s DVA until 2007 then encompassing the CD DVD and Blu ray systems In the early 1960s the Music Corporation of America bought Gregg s patents and his company Gauss Electrophysics American inventor James T Russell has been credited with inventing the first system to record a digital signal on an optical transparent foil that is lit from behind by a high power halogen lamp Russell s patent application was first filed in 1966 and he was granted a patent in 1970 Following litigation Sony and Philips licensed Russell s patents then held by a Canadian company Optical Recording Corp in the 1980s Both Gregg s and Russell s disc are floppy media read in transparent mode which imposes serious drawbacks after this were developed four generations of optical drive that includes Laserdisc 1969 WORM 1979 Compact Discs 1984 DVD 1995 Blu ray 2005 HD DVD 2006 more formats are currently under development First generation From the start optical discs were used to store broadcast quality analog video and later digital media such as music or computer software The LaserDisc format stored analog video signals for the distribution of home video but commercially lost to the VHS videocassette format due mainly to its high cost and non re recordability other first generation disc formats were designed only to store digital data and were not initially capable of use as a digital video medium Most first generation disc devices had an infrared laser reading head The minimum size of the laser spot is proportional to the wavelength of the laser so wavelength is a limiting factor upon the amount of information that can be stored in a given physical area on the disc The infrared range is beyond the long wavelength end of the visible light spectrum so it supports less density than shorter wavelength visible light One example of high density data storage capacity achieved with an infrared laser is 700 MB of net user data for a 12 cm compact disc Other factors that affect data storage density include the existence of multiple layers of data on the disc the method of rotation Constant linear velocity CLV Constant angular velocity CAV or zoned CAV the composition of lands and pits and how much margin is unused is at the center and the edge of the disc Types of Optical Discs Compact disc CD and derivatives Audio CD Video CD VCD Super Video CD CD Video CD Interactive LaserDisc GD ROM Phase change Dual Double Density Compact Disc DDCD Magneto optical disc MiniDisc MD MD Data Write Once Read Many WORM Laserdisc In the Netherlands in 1969 Philips Research physicist Pieter Kramer invented an optical videodisc in reflective mode with a protective layer read by a focused laser beam U S patent 5 068 846 filed 1972 issued 1991 Kramer s physical format is used in all optical discs In 1975 Philips and MCA began to work together and in 1978 commercially much too late they presented their long awaited Laserdisc in Atlanta MCA delivered the discs and Philips the players However the presentation was a commercial failure and the cooperation ended In Japan and the U S Pioneer succeeded with the Laserdisc until the advent of the DVD In 1979 Philips and Sony in consortium successfully developed the audio compact disc WORM drive In 1979 Exxon STAR Systems in Pasadena CA built a computer controlled WORM drive that utilized thin film coatings of Tellurium and Selenium on a 12 diameter glass disk The recording system utilized blue light at 457 nm to record and red light at 632 8 nm to read STAR Systems was bought by Storage Technology Corporation STC in 1981 and moved to Boulder CO Development of the WORM technology was continued using 14 diameter aluminum substrates Beta testing of the disk drives originally labeled the Laser Storage Drive 2000 LSD 2000 was only moderately successful Many of the disks were shipped to RCA Laboratories now David Sarnoff Research Center to be used in the Library of Congress archiving efforts The STC disks utilized a sealed cartridge with an optical window for protection U S patent 4 542 495 CD ROM The CD ROM format was developed by Sony and Philips introduced in 1984 as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data The same year Sony demonstrated a LaserDisc data storage format with a larger data capacity of 3 28 GB In the late 1980s and early 1990s Optex Inc of Rockville MD built an erasable optical digital video disc system U S patent 5 113 387 using Electron Trapping Optical Media ETOM U S patent 5 128 849 Although this technology was written up in Video Pro Magazine s December 1994 issue promising the death of the tape it was never marketed Magnetic disks found limited applications in storing the data in large amount So there was the need of finding some more data storing techniques As a result it was found that by using optical means large data storing devices can be made that in turn gave rise to the optical discs The very first application of this kind was the compact disc CD which was used in audio systems Sony and Philips developed the first generation of the CDs in the mid 1980s with the complete specifications for these devices With the help of this kind of technology the possibility of representing the analog signal into digital signal was exploited to a great level For this purpose the 16 bit samples of the analog signal were taken at the rate of 44 100 samples per second This sample rate was based on the Nyquist rate of 40 000 samples per second required to capture the audible frequency range to 20 kHz without aliasing with an additional tolerance to allow the use of less than perfect analog audio pre filters to remove any higher frequencies The first version of the standard allowed up to 74 minutes of music or 650 MB of data storage Second generation Second generation optical discs were for storing great amounts of data including broadcast quality digital video Such discs usually are read with a visible light laser usually red the shorter wavelength and greater numerical aperture allow a narrower light beam permitting smaller pits and lands in the disc In the DVD format this allows 4 7 GB storage on a standard 12 cm single sided single layer disc alternatively smaller media such as the DataPlay format can have capacity comparable to that of the larger standard compact 12 cm disc DVD and derivatives DVD Audio DualDisc Digital Video Express DIVX DVD RAM DVD R Nintendo GameCube Game Disc miniDVD derivative Wii Optical Disc DVD derivative Super Audio CD SACD Enhanced Versatile Disc DataPlay Hi MD Universal Media Disc UMD Ultra Density OpticalDVD ROM In 1995 a consortium of manufacturers Sony Philips Toshiba Panasonic developed the second generation of the optical disc the DVD The DVD disc appeared after the CD ROM had become widespread in society Third generation Third generation optical discs are used for distributing high definition video and videogames and support greater data storage capacities accomplished with short wavelength visible light lasers and greater numerical apertures Blu ray Disc and HD DVD uses blue violet lasers and focusing optics of greater aperture for use with discs with smaller pits and lands thereby greater data storage capacity per layer In practice the effective multimedia presentation capacity is improved with enhanced video data compression codecs such as H 264 MPEG 4 AVC and VC 1 Blu ray and derivatives up to 400 GB experimental BD R and BD RE High Fidelity Pure Audio AVCHD and AVCREC BDXL and Blu ray 3D 4K Blu ray and 8K Blu ray Wii U Optical Disc 25 GB per layer HD DVD discontinued disc format up to 51 GB triple layer CBHD a derivative of the HD DVD format HD VMD Professional Disc Announced but not released Digital Multilayer Disk Fluorescent Multilayer Disc Forward Versatile DiscBlu ray and HD DVD The third generation optical disc was developed in 2000 2006 and was introduced as Blu ray Disc First movies on Blu ray Discs were released in June 2006 Blu ray eventually prevailed in a high definition optical disc format war over a competing format the HD DVD A standard Blu ray disc can hold about 25 GB of data a DVD about 4 7 GB and a CD about 700 MB Comparison of various optical storage mediaFourth generation The following formats go beyond the current third generation discs and have the potential to hold more than one terabyte 1 TB of data and at least some are meant for cold data storage in data centers dubious discuss Archival Disc Holographic Versatile Disc Announced but not released LS R Protein coated disc Stacked Volumetric Optical Disc 5D DVD 3D optical data storage not a single technology examples are Hyper CD ROM and Fluorescent Multilayer Disc In 2004 development of the Holographic Versatile Disc HVD commenced which promised the storage of several terabytes of data per disc However development stagnated towards the late 2000s due to lack of funding In 2006 it was reported that Japanese researchers developed ultraviolet ray lasers with a wavelength of 210 nanometers which would enable a higher bit density than Blu ray discs As of 2022 no updates on that project have been reported Overview of optical types Name Capacity Experimental YearsLaserDisc LD N A 1971 2007Write Once Read Many Disk WORM 0 2 6 0 GB 1979 1984Compact disc CD 0 7 0 9 GB 1982 presentElectron Trapping Optical Memory ETOM 6 0 12 0 GB 1987 1996MiniDisc MD 0 14 1 0 GB 1989 2025Magneto Optical Disc MOD 0 1 16 7 GB 1990 presentDigital Versatile Disc DVD 4 7 17 GB 1995 presentLIMDOW Laser Intensity Modulation Direct OverWrite 2 6 GB 10 GB 1996 presentGD ROM 1 2 GB 1997 2006Fluorescent Multilayer Disc 50 140 GB 1998 2003Versatile Multilayer Disc VMD 5 20 GB 100 GB 1999 2010Hyper CD ROM 1 PB 100 EB 1999 presentDataPlay 500 MB 1999 2006Ultra Density Optical UDO 30 60 GB 2000 presentForward Versatile Disc FVD 5 4 15 GB 2005 2006Enhanced Versatile Disc EVD DVD 2002 2004HD DVD 15 51 GB 1 TB citation needed 2002 2008Blu ray Disc BD 25 GB 50 GB 2002 presentBDXL 100 GB 128 GB 1 TB 2010 presentProfessional Disc for Data PDD 23 GB 2003 2006Professional Disc 23 128 GB 2003 presentDigital Multilayer Disk 22 32 GB 2004 2007Multiplexed Optical Data Storage MODS Disc 250 GB 1 TB 2004 presentUniversal Media Disc UMD 0 9 1 8 GB 2004 2014Holographic Versatile Disc HVD 6 0 TB 2004 2012Protein coated disc PCD 50 TB 2005 2006M DISC 4 7 GB DVD format 25 GB Blu ray format 50 GB Blu ray format 100 GB BDXL format 2009 presentArchival Disc 0 3 1 TB 2014 presentUltra HD Blu ray 50 GB 66 GB 100 GB 128 GB 2015 presentNotesPrototypes and theoretical values Years from known start of development till end of sales or development Recordable and writable optical discsThere are numerous formats of optical direct to disk recording devices on the market all of which are based on using a laser to change the reflectivity of the digital recording medium in order to duplicate the effects of the pits and lands created when a commercial optical disc is pressed Formats such as CD R and DVD R are Write once read many or write once while CD RW and DVD RW are rewritable more like a magnetic recording hard disk drive HDD Media technologies vary for example M DISC media uses a rock like layer to retain data for longer than conventional recordable media While being read only compatible with existing DVD and Blu ray drives M DISC media can only be written to using a stronger laser specifically made for this purpose which is built into fewer optical drive models Surface error scanningError rate measurement on a DVD R The error rate is still within a healthy range This section needs expansion You can help by adding to it July 2020 Optical media can predictively be scanned for errors and media deterioration well before any data becomes unreadable Optical formats include some redundancy for error correction which works until the amount of error exceeds a threshold A higher rate of errors may indicate deteriorating and or low quality media physical damage an unclean surface and or media written using a defective optical drive Precise error scanning requires access to the raw uncorrected readout of a disc which is not always provided by a drive As a result support of this functionality varies per optical drive manufacturer and model On ordinary drives without this functionality it is possible to still look for unexpected reduction in read speed as an indirect much less reliable measure Optical media such as CDs and DVDs can be scanned to detect errors and signs of deterioration well before data becomes unreadable These formats include built in error correction mechanisms which function by adding redundant data However once the rate of errors surpasses the correction threshold the media becomes vulnerable to failure A high error rate can signal physical deterioration low quality manufacturing surface contamination or data recorded by a faulty optical drive Accurate error scanning requires access to a disc s raw uncorrected readout However not all optical drives provide this capability and support for this feature can vary significantly between manufacturers and drive models On drives lacking raw data access users may rely on a less precise method monitoring unexpected reductions in read speed though this is a far less reliable indicator of disc health Several specialized tools are available for performing error scans on optical media Popular programs include Nero DiscSpeed K Probe Opti Drive Control previously known as CD Speed 2000 and DVD Info Pro for Windows For cross platform users QPxTool is available to help monitor and maintain optical media integrity Each of these tools allows for detailed analysis of the error rates and conditions affecting optical discs Error types There are different types of error measurements including so called C1 C2 and CU errors on CDs and PI PO parity inner outer errors and the more critical PI PO failures on DVDs Finer grain error measurements on CDs supported by very few optical drives are called E11 E21 E31 E21 E22 E32 CU and POF represent uncorrectable errors on data CDs and DVDs respectively thus data loss and can be a result of too many consecutive smaller errors Due to the weaker error correction used on Audio CDs Red Book standard and Video CDs White Book standard C2 errors already lead to data loss However even with C2 errors the damage is inaudible to some extent Blu ray discs use so called LDC Long Distance Codes and BIS Burst Indication Subcodes error parameters According to the developer of the Opti Drive Control software a disc can be considered healthy at an LDC error rate below 13 and BIS error rate below 15 Optical disc manufacturingOptical discs are made using replication This process can be used with all disc types Recordable discs have pre recorded vital information like manufacturer disc type maximum read and write speeds etc In replication a cleanroom with yellow light is necessary to protect the light sensitive photoresist and to prevent dust from corrupting the data on the disc A glass master is used in replication The master is placed in a machine that cleans it as much as possible using a rotating brush and deionized water preparing it for the next step In the next step a surface analyzer inspects the cleanliness of the master before photoresist is applied on the master The photoresist is then baked in an oven to solidify it Then in the exposure process the master is placed in a turntable where a laser selectively exposes the resist to light At the same time a developer and deionized water are applied to the disc to remove the exposed resist This process forms the pits and lands that represent the data on the disc A thin coating of metal is then applied to the master making a negative of the master with the pits and lands in it The negative is then peeled off the master and coated in a thin layer of plastic The plastic protects the coating while a punching press punches a hole into the center of the disc and punches excess material The negative is now a stamper a part of the mold that will be used for replication It is placed on one side of the mold with the data side containing the pits and lands facing out This is done inside an injection molding machine The machine then closes the mold and injects polycarbonate in the cavity formed by the walls of the mold which forms or molds the disc with the data on it The molten polycarbonate fills the pits or spaces between the lands on the negative acquiring their shape when it solidifies This step is somewhat similar to record pressing The polycarbonate disc cools quickly and is promptly removed from the machine before forming another disc The disc is then metallized covered with a thin reflective layer of aluminum The aluminum fills the space once occupied by the negative A layer of varnish is then applied to protect the aluminum coating and provide a surface suitable for printing The varnish is applied near the center of the disc and the disc is spun evenly distributing the varnish on the surface of the disc The varnish is hardened using UV light The discs are then silkscreened or a label is otherwise applied Recordable discs add a dye layer and rewritable discs add a phase change alloy layer instead which is protected by upper and lower dielectric electrically insulating layers The layers may be sputtered The additional layer is between the grooves and the reflective layer of the disc Grooves are made in recordable discs in place of the traditional pits and lands found in replicated discs and the two can be made in the same exposure process In DVDs the same processes as in CDs are carried out but in a thinner disc The thinner disc is then bonded to a second equally thin but blank disc using UV curable Liquid optically clear adhesive forming a DVD disc This leaves the data in the middle of the disc which is necessary for DVDs to achieve their storage capacity In multi layer discs semi reflective instead of reflective coatings are used for all layers except the last layer which is the deepest one and uses a traditional reflective coating Dual layer DVDs are made slightly differently After metallization with a thinner metal layer to allow some light to pass through base and pit transfer resins are applied and pre cured in the center of the disc Then the disc is pressed again using a different stamper and the resins are completely cured using UV light before being separated from the stamper Then the disc receives another thicker metallization layer and is then bonded to the blank disc using LOCA glue DVD R DL and DVD R DL discs receive a dye layer after curing but before metallization CD R DVD R and DVD R discs receive the dye layer after pressing but before metallization CD RW DVD RW and DVD RW receive a metal alloy layer sandwiched between 2 dielectric layers HD DVD is made in the same way as DVD In recordable and rewritable media most of the stamper is composed of grooves not pits and lands The grooves contain a wobble frequency that is used to locate the position of the reading or writing laser on the disc DVDs use pre pits instead with a constant frequency wobble Blu ray HTL high to low type Blu ray discs are made differently First a silicon wafer is used instead of a glass master The wafer is processed in the same way a glass master would The wafer is then electroplated to form a 300 micron thick nickel stamper which is peeled off from the wafer The stamper is mounted onto a mold inside a press or embosser The polycarbonate discs are molded in a similar fashion to DVD and CD discs If the discs being produced are BD Rs or BD REs the mold is fitted with a stamper that stamps a groove pattern onto the discs in lieu of the pits and lands found on BD ROM discs After cooling a 35 nanometre thick layer of silver alloy is applied to the disc using sputtering Then the second layer is made by applying base and pit transfer resins to the disc and are pre cured in its center After application and pre curing the disc is pressed or embossed using a stamper and the resins are immediately cured using intense UV light before the disc is separated from the stamper The stamper contains the data that will be transferred to the disc This process is known as embossing and is the step that engraves the data onto the disc replacing the pressing process used in the first layer and it is also used for multi layer DVD discs Then a 30 nanometre thick layer of silver alloy is then sputtered onto the disc and the process is repeated as many times as required Each repetition creates a new data layer The resins are applied again pre cured stamped with data or grooves and cured silver alloy is sputtered and so on BD R and BD RE discs receive through sputtering a metal recording layer alloy that is sandwiched between two dielectric layers also sputtered in BD RE before receiving the 30 nanometre metallization silver alloy aluminum or gold layer which is sputtered Alternatively the silver alloy may be applied before the recording layer is applied Silver alloys are usually used in Blu rays and aluminum is usually used on CDs and DVDs Gold is used in some Archival CDs and DVDs since it is more chemically inert and resistant to corrosion than aluminum which corrodes into aluminum oxide which can be seen in disc rot as transparent patches or dots in the disc that prevent the disc from being read since the laser light passes through the disc instead of being reflected back into the laser pickup assembly to be read Normally aluminum does not corrode since it has a thin oxide layer that forms on contact with oxygen In this case it can corrode due to its thinness Then the 98 micron thick cover layer is applied using UV curable liquid optically clear adhesive and a 2 micron thick hard coat such as Durabis is also applied and cured using UV light In the last step a 10 nanometre thick silicon nitride barrier layer is applied to the label side of the disc to protect against humidity Blu rays have their data very close to the read surface of the disc which is necessary for Blu rays to achieve their capacity Discs in large quantities can either be replicated or duplicated In replication the process explained above is used to make the discs while in duplication CD R DVD R or BD R discs are recorded and finalized to prevent further recording and allow for wider compatibility See Optical disc authoring The equipment is also different replication is carried out by fully automated purpose built machinery whose cost is in the hundreds of thousands of US dollars in the used market while duplication can be automated using what s known as an autoloader or be done by hand and only requires a small tabletop duplicator SpecificationsBase 1 and current maximum speeds by generation Generation Base Max Mbit s Mbit s 1st CD 1 17 65 6 56 2nd DVD 10 57 253 6 24 3rd BD 36 504 14 4th AD 14 Capacity and nomenclature Designation Sides Layers total Diameter Capacity cm GB BD SS SL 1 1 8 7 8BD SS DL 1 2 8 15 6BD SS SL 1 1 12 25BD SS DL 1 2 12 50BD SS TL 1 3 12 100BD SS QL 1 4 12 128CD ROM 74 min SS SL 1 1 12 0 682CD ROM 80 min SS SL 1 1 12 0 737CD ROM SS SL 1 1 8 0 194DDCD ROM SS SL 1 1 12 1 364DDCD ROM SS SL 1 1 8 0 387DVD 1 SS SL 1 1 8 1 46DVD 2 SS DL 1 2 8 2 66DVD 3 DS SL 2 2 8 2 92DVD 4 DS DL 2 4 8 5 32DVD 5 SS SL 1 1 12 4 70DVD 9 SS DL 1 2 12 8 54DVD 10 DS SL 2 2 12 9 40DVD 14 DS DL SL 2 3 12 13 24DVD 18 DS DL 2 4 12 17 08DVD R 1 0 SS SL 1 1 12 3 95DVD R 2 0 R RW RW SS SL 1 1 12 4 7DVD R R RW RW DS SL 2 2 12 9 40DVD RAM SS SL 1 1 8 1 46DVD RAM DS SL 2 2 8 2 65DVD RAM 1 0 SS SL 1 1 12 2 58DVD RAM 2 0 SS SL 1 1 12 4 70DVD RAM 1 0 DS SL 2 2 12 5 16DVD RAM 2 0 DS SL 2 2 12 9 40See alsoDisc Description Protocol List of optical disc manufacturers Universal Disk Format UDF ReferencesShinya Yoshioka 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