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| Computer memory and Computer data storage types |
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| Optical discs |
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An optical disc is a flat, usually[note 1] 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.[1][2] 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.[3] 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 (e.g.: CD and CD-ROM), recordable (write-once, e.g. CD-R), or re-recordable (rewritable, e.g. 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[4]) 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.[5] 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.
Usage
Optical discs are often stored in special cases sometimes called jewel cases and are most commonly used for digital preservation, storing music (e.g. for use in a CD player), video (e.g. 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.[6][citation needed] 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.[7] 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.
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 18938:2008 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.
Safety
As the media itself only is accessed through a laser beam, no internal control circuitry, it can not contain malicious hardware such as so-called rubber-duckies or USB killers.
Malware is unable to spread over factory-pressed media, finalized media, or -ROM (read-only memory) drive types whose lasers lack the strength to write data. Malware is conventionally programmed to detect and spread over traditional mass storage devices such as flash drives, external solid-state drives and hard disk drives.[8]
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.[9]
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.[10]
An early analogue optical disc system existed in 1935, used on Welte's Lichttonorgel sampling organ.[11]
An early analog optical disc used for video recording was invented by David Paul Gregg in 1958[12] 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.[13][14][15]
Both Gregg's and Russell's disc are floppy media read in transparent mode, which imposes serious drawbacks. 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.
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.
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.[16]
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.
In the mid-1990s, a consortium of manufacturers (Sony, Philips, Toshiba, Panasonic) developed the second generation of the optical disc, the DVD.[17]
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.[18] The first version of the standard allowed up to 75 minutes of music, which required 650 MB of storage.
The DVD disc appeared after the CD-ROM had become widespread in society.
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.[19] 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.
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
- LaserDisc
- GD-ROM
- Phase-change Dual
- Double Density Compact Disc (DDCD)
- Magneto-optical disc
- MiniDisc (MD)
- Write Once Read Many (WORM)
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[20] 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.[21]
- DVD and derivatives
- 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
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.[20] 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[22][23])
- BD-R and BD-RE
- High Fidelity Pure Audio
- AVCHD and AVCREC
- BDXL and Blu-ray 3D
- 4K Blu-ray and 8K Blu-ray[24]
- 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:
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:[25][dubious ]
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.[26] As of 2022, no updates on that project have been reported.
Folio Photonics is planning to release high-capacity discs in 2024 with the cost of $5 per TB, with a roadmap to $1 per TB, using 80% less power than HDD.[27]
Overview of optical types
| Name | Capacity | Experimental[Note 1] | Years[Note 2] |
|---|---|---|---|
| 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–present | |
| 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 | 2001–present | |
| 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) | Zdroj:https://en.wikipedia.org?pojem=Optical_media |