There are several different types of memory:
RAM (random-access memory): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
ROM (read-only memory): Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.
PROM (programmable read-only memory): A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.
EPROM (erasable programmable read-only memory): An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.
EEPROM (electrically erasable programmable read-only memory): An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge
Types of CDs(640MB/700MB)
(Diameter 12cm ,Thickness 1.2cm)
CD- ROM = Compact Disc Read Only Memory
A CD-ROM an acronym of "Compact Disc Read-only memory") is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data.[2]
CD-ROMs are popularly used to distribute computer software, including video games and multimedia applications, though any data can be stored (up to the capacity limit of a disc). Some CDs hold both computer data and audio with the latter capable of being played on a CD player, while data (such as software or digital video) is only usable on a computer (such as ISO 9660 format PC CD-ROMs). These are called enhanced CDs.
Even though many people use lowercase letters in this acronym, proper presentation is in all capital letters with a hyphen between CD and ROM. At the time of the technology's introduction it had more capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding CDs, DVDs and Blu-ray, though some experimental descendants of it such as HVDs may have more space and faster data rates than today's largest hard drive
.
CD-R = Compact Disc Recordable (Once)
A CD-R (Compact Disc-Recordable) is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many (WORM) optical medium, although the whole disk does not have to be entirely written in the same session.
CD-R retains a high level of compatibility with standard CD readers, unlike CD-RW which can be re-written, but is not capable of playing on many readers.
CD-RW= Compact Disc Rewritable (Many time)
A CD-RW (Compact Disc-ReWritable) is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released.
CD-RW disc require a more sensitive laser optics. Also, CD-RWs cannot be read in some CD-ROM drives built prior to 1997. CD-ROM drives will bear a "MultiRead" certification to show compatibility. CD-RW discs need to be blanked before reuse. Different blanking methods can be used, including "full" blanking in which the entire surface of the disc is cleared, and "fast" blanking in which only meta-data areas are cleared: PMA, TOC and pregap, comprising a few percent of the disc. Fast blanking is much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces of the former data, often for confidentiality. It may be possible to recover data from full-blanked CD-RWs with specialty data recovery equipment[citation needed]; however, this is generally not used except by government agencies due to cost.
CD-RW also have a shorter rewriting cycles life (ca. 1,000) compared to virtually all of the previously exposed types storage of media (typically well above 10,000 or even 100,000), something which however is less of a drawback considering that CD-RWs are usually written and erased in their totality, and not with repeated small scale changes, so normally wear leveling is not an issue.
Their ideal usage field is in the creation of test disks, temporary short or mid-term backups, and in general, where an intermediate solution between online and offline storage schemes is required.
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A CD-ROM an acronym of "Compact Disc Read-only memory") is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data.[2]
CD-ROMs are popularly used to distribute computer software, including video games and multimedia applications, though any data can be stored (up to the capacity limit of a disc). Some CDs hold both computer data and audio with the latter capable of being played on a CD player, while data (such as software or digital video) is only usable on a computer (such as ISO 9660 format PC CD-ROMs). These are called enhanced CDs.
Even though many people use lowercase letters in this acronym, proper presentation is in all capital letters with a hyphen between CD and ROM. At the time of the technology's introduction it had more capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding CDs, DVDs and Blu-ray, though some experimental descendants of it such as HVDs may have more space and faster data rates than today's largest hard drive
.
CD-R = Compact Disc Recordable (Once)
A CD-R (Compact Disc-Recordable) is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many (WORM) optical medium, although the whole disk does not have to be entirely written in the same session.
CD-R retains a high level of compatibility with standard CD readers, unlike CD-RW which can be re-written, but is not capable of playing on many readers.
CD-RW= Compact Disc Rewritable (Many time)
A CD-RW (Compact Disc-ReWritable) is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released.
CD-RW disc require a more sensitive laser optics. Also, CD-RWs cannot be read in some CD-ROM drives built prior to 1997. CD-ROM drives will bear a "MultiRead" certification to show compatibility. CD-RW discs need to be blanked before reuse. Different blanking methods can be used, including "full" blanking in which the entire surface of the disc is cleared, and "fast" blanking in which only meta-data areas are cleared: PMA, TOC and pregap, comprising a few percent of the disc. Fast blanking is much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces of the former data, often for confidentiality. It may be possible to recover data from full-blanked CD-RWs with specialty data recovery equipment[citation needed]; however, this is generally not used except by government agencies due to cost.
CD-RW also have a shorter rewriting cycles life (ca. 1,000) compared to virtually all of the previously exposed types storage of media (typically well above 10,000 or even 100,000), something which however is less of a drawback considering that CD-RWs are usually written and erased in their totality, and not with repeated small scale changes, so normally wear leveling is not an issue.
Their ideal usage field is in the creation of test disks, temporary short or mid-term backups, and in general, where an intermediate solution between online and offline storage schemes is required.
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Types of DVDs (Digital Versatile Disc)
Single Side Single layer = 4.5GB
Double Side Single layer = 9.4GB
Single Side Double layer = 8.54GB
Double Side Double layer = 17GB
DVD-R/RW Formats
Five types of recordable DVD products currently exist on the market. Some are approved and supported by the DVD Forum and some are not. Industry standard and recognised
by the
DVD Forum:
DVD-R = DVD Recordable
DVD-R is a DVD recordable format. A DVD-R typically has a storage capacity of 4.71 GB. Pioneer has also developed an 8.5 GB dual layer version, DVD-R DL, which appeared on the market in 2005.
Data on a DVD-R cannot be changed, whereas a DVD-RW (rewritable DVD) can be rewritten multiple (1000+) times. DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM.
Technical specifications
The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer a red laser beam with a wavelength of 640 nm (for general use recordable DVD, versus a wavelength of 780 nm for CD-R) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, DVD-R and DVD+R use different dyes from CD-R to properly absorb this wavelength.
DVD-R discs are composed of two 0.6 mm acrylic discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved 'dummy' disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. The sandwich structure also helps protect the data containing layer from scratches with a thick 'dummy' disc, a problem with CDs, which lack that structure. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD's 1.2 mm of acrylic, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size to write smaller pits.
In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control, etc.
In 2011, JVC announced an archival DVD recording media manufactured with quality control and inspection frequencies techniques greater than is traditionally used in media manufacturing, and using specially developed silver alloy as a reflective layer and organic dye with in-house developed additives to secure long-term data retention
Double Side Single layer = 9.4GB
Single Side Double layer = 8.54GB
Double Side Double layer = 17GB
DVD-R/RW Formats
Five types of recordable DVD products currently exist on the market. Some are approved and supported by the DVD Forum and some are not. Industry standard and recognised
by the
DVD Forum:
DVD-R = DVD Recordable
DVD-R is a DVD recordable format. A DVD-R typically has a storage capacity of 4.71 GB. Pioneer has also developed an 8.5 GB dual layer version, DVD-R DL, which appeared on the market in 2005.
Data on a DVD-R cannot be changed, whereas a DVD-RW (rewritable DVD) can be rewritten multiple (1000+) times. DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM.
Technical specifications
The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer a red laser beam with a wavelength of 640 nm (for general use recordable DVD, versus a wavelength of 780 nm for CD-R) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, DVD-R and DVD+R use different dyes from CD-R to properly absorb this wavelength.
DVD-R discs are composed of two 0.6 mm acrylic discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved 'dummy' disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. The sandwich structure also helps protect the data containing layer from scratches with a thick 'dummy' disc, a problem with CDs, which lack that structure. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD's 1.2 mm of acrylic, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size to write smaller pits.
In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control, etc.
In 2011, JVC announced an archival DVD recording media manufactured with quality control and inspection frequencies techniques greater than is traditionally used in media manufacturing, and using specially developed silver alloy as a reflective layer and organic dye with in-house developed additives to secure long-term data retention
DVD-RW = DVD Rewritable
A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The smaller Mini DVD-RW holds 1.46 GB, with a diameter of 8 cm.
The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement. DVD-RW discs are commonly used to store data in a non-volatile format, such as when creating backups or collections of files. They are also increasingly used for home DVD video recorders. One benefit to using a rewritable disc is if there are writing errors when recording data, the disc is not ruined and can still store data by erasing the faulty data.
One competing rewritable format is DVD+RW. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular due to the lack of a single standard for recordable DVDs.
The recording layer in DVD-RW and DVD+RW is not an organic dye, but a special phase change metal alloy, often GeSbTe. The alloy can be switched back and forth between a crystalline phase and an amorphous phase, changing the reflectivity, depending on the power of the laser beam. Data can thus be written, erased and re-written.
Drive Specifications
Standard DVD-R/RW compatible drives use a 650nm red semiconductor laser diode. The average power consumption rating is 250mW to 400mW. Power consumption varies depending on the write speeds and dual layer support. Higher speed drives require more power for increased data throughput, and dual layer disks require more power to penetrate to the second layer of data.
Dual layer
A specification for dual-layer DVD-RW discs with a capacity of 8.5 GB was approved by the DVD Forum.[1] However, manufacturing support for rewritable dual-layer discs did not materialize due to costs and expected competition from newer and higher-capacity formats like Blu-ray and HD DVD.
DVD-RAM = DVD Random Access Memory
DVD-RAM (DVD–Random Access Memory) is a disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998.
Design
DVD-RAM is one of three competing technologies for rewritable DVDs. Its competitors are DVD-RW and DVD+RW. DVD-RAM technology provides excellent data integrity, data retention and damage protection through a number of mechanisms and properties. Therefore, DVD-RAM is perceived by some people[who?] to be better than the other DVD technologies for traditional computer usage tasks such as general data storage, and especially data backup and archival. The Mount Rainier Format standard and SecurDisc for DVD+/-RW (which also works on DVD-RAM, CD-R, and CD-RW) somewhat lessens the DVD-RAM format's perceived advantage in the data integrity category, but not in the data retention or damage protection categories.
DVD-RAM has a larger presence in camcorders and set-top boxes than in computers[citation needed], although the popularity of DVD-RAM in these devices can be explained by its being very easily written to and erased, which for example allows extensive in-camera editing.
The on-disc structure of DVD-RAM is closely related to hard disk and floppy disk technology, as it stores data in concentric tracks. DVD-RAMs can be accessed just like a hard or floppy disk and usually without any special software. DVD-RWs and DVD+RWs, on the other hand, store data in one long spiral track and require special packet reading/writing software to read and write data discs. Like magneto-optical (MO) technologies, DVD-RAM has numerous rectangles on the disc surface that define the boundaries of data sectors. However, DVD-RAM is not MO but a phase change medium, similar to CD-RW, DVD-RW, or DVD+RW.
A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The smaller Mini DVD-RW holds 1.46 GB, with a diameter of 8 cm.
The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement. DVD-RW discs are commonly used to store data in a non-volatile format, such as when creating backups or collections of files. They are also increasingly used for home DVD video recorders. One benefit to using a rewritable disc is if there are writing errors when recording data, the disc is not ruined and can still store data by erasing the faulty data.
One competing rewritable format is DVD+RW. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular due to the lack of a single standard for recordable DVDs.
The recording layer in DVD-RW and DVD+RW is not an organic dye, but a special phase change metal alloy, often GeSbTe. The alloy can be switched back and forth between a crystalline phase and an amorphous phase, changing the reflectivity, depending on the power of the laser beam. Data can thus be written, erased and re-written.
Drive Specifications
Standard DVD-R/RW compatible drives use a 650nm red semiconductor laser diode. The average power consumption rating is 250mW to 400mW. Power consumption varies depending on the write speeds and dual layer support. Higher speed drives require more power for increased data throughput, and dual layer disks require more power to penetrate to the second layer of data.
Dual layer
A specification for dual-layer DVD-RW discs with a capacity of 8.5 GB was approved by the DVD Forum.[1] However, manufacturing support for rewritable dual-layer discs did not materialize due to costs and expected competition from newer and higher-capacity formats like Blu-ray and HD DVD.
DVD-RAM = DVD Random Access Memory
DVD-RAM (DVD–Random Access Memory) is a disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998.
DesignDVD-RAM is one of three competing technologies for rewritable DVDs. Its competitors are DVD-RW and DVD+RW. DVD-RAM technology provides excellent data integrity, data retention and damage protection through a number of mechanisms and properties. Therefore, DVD-RAM is perceived by some people[who?] to be better than the other DVD technologies for traditional computer usage tasks such as general data storage, and especially data backup and archival. The Mount Rainier Format standard and SecurDisc for DVD+/-RW (which also works on DVD-RAM, CD-R, and CD-RW) somewhat lessens the DVD-RAM format's perceived advantage in the data integrity category, but not in the data retention or damage protection categories.
DVD-RAM has a larger presence in camcorders and set-top boxes than in computers[citation needed], although the popularity of DVD-RAM in these devices can be explained by its being very easily written to and erased, which for example allows extensive in-camera editing.
The on-disc structure of DVD-RAM is closely related to hard disk and floppy disk technology, as it stores data in concentric tracks. DVD-RAMs can be accessed just like a hard or floppy disk and usually without any special software. DVD-RWs and DVD+RWs, on the other hand, store data in one long spiral track and require special packet reading/writing software to read and write data discs. Like magneto-optical (MO) technologies, DVD-RAM has numerous rectangles on the disc surface that define the boundaries of data sectors. However, DVD-RAM is not MO but a phase change medium, similar to CD-RW, DVD-RW, or DVD+RW.