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Optical storage is a class ofdata storage systems that use light to read or write data to an underlyingoptical media. Although a number of optical formats have been used over time, the most common examples areoptical disks like the compact disc (CD) and digital versatile disc (DVD). Reading and writing methods have also varied over time, but most modern systems as of 2023[update] uselasers as the light source and use it both for reading and writing to the discs.[1]Britannica notes that it "uses low-power laser beams to record and retrieve digital (binary) data."[2][3]
Optical storage is thestorage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam oflaser light precisely focused on a spinningoptical disc. An older example of optical storage that does not require the use of computers, ismicroform. There are other means of optically storing data and new methods are in development. Anoptical disc drive is a device in a computer that can readCD-ROMs or otheroptical discs, such as DVDs andBlu-ray discs. Optical storage differs from other data storage techniques that make use of other technologies such asmagnetism, such asfloppy disks andhard disks, orsemiconductors, such asflash memory.
Optical storage in the form of discs grants the ability to record onto a compact disc in real time. Compact discs held many advantages overaudio tape players, such as higher sound quality and the ability to play backdigital sound.[4] Optical storage also gained importance for itsgreen qualities and its efficiency with high energies.[5]
Optical storage can range from a single drive reading a single CD-ROM to multiple drives reading multiple discs such as anoptical jukebox. Single CDs (compact discs) can hold around 700 MB (megabytes) and optical jukeboxes can hold much more. Single-layer DVDs can hold 4.7 GB, while dual-layered can hold 8.5 GB. This can be doubled to 9.4 GB and 17 GB by making the DVDs double-sided, with readable surfaces on both sides of the disc. HD DVDs were able to store 15 GB with a single-layer and 30 GB with a dual-layer. Blu-ray discs, which won the HDTV opticalformat war by defeating HD DVDs, can hold 25 GB for single-layer, 50 GB for dual-layer and up to 128 GB for quad-layer discs. Optical storage includes CDs and DVDs.
IBM was a leader in the development of optical storage systems for much of the early history of computing. In 1959, they installed theAutomatic Language Translator, which used an optical disk holding 170,000 words and phrases in Russian and their translations in English.[6] In 1961/2, they introduced theIBM 1360, which used small photographic slides that were read using a conventionalincandescent lamp as a light source and aphotocell as a detector. A separate system wrote data to the slides using anelectron gun, making it a read/write system. Fully expanded, the 1360 could hold about a half a terabit of data and allowed for semi-random access.[7] A similar 3rd party system was theFoto-Mem FM 390.
Various forms of optical media, mostly disk form, competed withmagnetic recording through most of the 1960s and 70s, but never became widely used. It was the introduction ofsemiconductor lasers that provided the technology needed to make optical storage more practical in bothstorage density and cost terms. Prices fell to the point that they could be used in consumer products, leading to the 1978 introduction of the analogLaserDisc format. This was followed in August 1982 by the introduction of thedigital audioaudio/music CD,[8] which soon led to an effort to standardize data recording on this media. This was introduced in 1985 as the"Yellow Book", which became known asCD-ROM.[9]
In 1983,Philips introduced their early work onmagneto-optical drive technology at an industry conference. This used a laser to warm the storage media so that it becamesusceptible to magnetic fields and an electromagnet, similar to the one in ahard drive, to write data by realigning the material within. It worked like a conventional optical drive during reads, with the laser operating at lower energy levels, too low to heat the disk. Rumors thatIBM would use this in future versions of theIBM PC were common for a time,[10] but nothing ever came of this.Canon introduced a version packaged in a jacket similar to those used for the 3.5-inchfloppy disk. Introduced in 1985, it found no major uses until 1988 when it was the centrepiece of theNeXT Computer.[11] Variations on this design were introduced through the 1990s but it never became very popular outside of Japan, althoughSony'sMiniDisc format saw some success.[12]
In 1988, the "Orange Book" added a write-once format, CD-WO, to the existing CD format. The media was compatible with existing CD drives, allowing music and data to be recorded and then read in any existing drive. Over time, this became known asCD-R.[9] In 1990, the Orange Book added magnetic-optical re-writable versions of the CD physical format,CD-MO, which differed from earlier MO systems primarily in that the disk was not enclosed in a jacket. This format saw little use. Continual improvements in drive and media led to the 1997 addition of theCD-RW format, which allowed disks to be written, erased and re-written. This format is incompatible with older CD drives, like CD-R, but read-only drives capable of reading CD-RW became common in the 2000s as CD-RW use proliferated.
Optical media took another large step with the 1996 introduction of DVD, which was to video what the CD was to music. Originally to be known as "digital video disc", the name changed before release to be "digital versatile disc" to indicate that it was also useful for computer storage.[13] Over time, DVDs followed a similar pattern as CDs;Pioneer introduced a write-once format in 1997 that could be read in existing DVD drives,DVD-R.[14] But a second write-once formatDVD+R emerged in 2002, leading to a briefformat war beforedual format drives became common. A read-write format,DVD-RW, was introduced in 1999, but like earlier CDs it could not be read by "normal" DVD drives. Over time, improvements led to most newer DVD drives being able to read any of these media.[15]
Another technical improvement during this era was the introduction of higher-frequency semiconductor lasers operating in the blue and near ultraviolet spectrum. These shorter wavelengths, combined with improvements in the underlying media, allowed much more data to be stored on a disk. With the widespread introduction ofhigh-definition television in the early 2000s, the need for a medium able to store the much larger higher-resolution video files became an issue,[16] leading to two competing standards,HD DVD andBlu-ray. The former could be produced on existing DVD production equipment but (initially) offered lower resolution video formats (and less data storage) while the later required new production equipment but offered1080p support. Over time, Blu-ray won the resultinghigh-definition optical disc format war, withToshiba announcing their withdrawal of HD DVD on February 19, 2008. This proved to be aPyrrhic victory as the market quickly moved tostreaming services. Blu-ray remains preferred to streaming services for its technical qualities, but has a tiny market share as of 2023[update].[17]
As of 2023[update], Blu-ray is the last major optical format to reach widespread use. The ever-increasing speed ofbroadband internet has replaced many of its roles as a distribution medium for media and video games, and the rapidly falling prices ofFlash memory through the 2010s did the same in its archival role with read-write formats. A number of new technologies have been proposed as the basis for a new optical standard, but have not seen widespread use. These include:
TheOptical Storage Technology Association (OSTA) was an internationaltrade association formed to promote the use of recordable optical data storage technologies and products.
optical media, such as compact discs (CDs) and DVDs.
On October 1, 1982, Sony ignited a digital audio revolution with the release of the world's first commercial compact disc player, the CDP-101 (above), in Japan.
Important Notice to the subscribers of the DVD-RW Format Specifications Book Ver.1.2
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