Optical drive

In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from certain discs, but recent drives can both read and record, also called burners or writers (since they physically burn the organic dye on write-once CD-R, DVD-R and BD-R LTH discs). Compact discs, DVDs, and Blu-ray discs are common types of optical media which can be read and recorded by such drives.

Drive types

, most of the optical disc drives on the market are DVD-ROM drives and BD-ROM drives which read and record from those formats, along with having backward compatibility with CD, CD-R and CD-ROM discs; compact disc drives are no longer manufactured outside of audio devices. Read-only DVD and Blu-ray drives are also manufactured, but are less commonly found in the consumer market and mainly limited to media devices such as game consoles and disc media players. Over the last ten years, laptop computers no longer come with optical disc drives in order to reduce costs and make devices lighter, requiring consumers to purchase external optical drives.

Appliances and functionality

Optical disc drives are an integral part of standalone appliances such as CD players, DVD players, Blu-ray Disc players, DVD recorders, certain desktop video game consoles, such as Sony PlayStation 4, Microsoft Xbox One, Nintendo Wii U, Sony PlayStation 5 and Xbox Series X and also in older consoles, such as the Sony PlayStation 3 and Xbox 360, and certain portable video game consoles, such as Sony PlayStation Portable (using proprietary now discontinued UMDs). They are also very commonly used in computers to read software and media distributed on disc and to record discs for archival and data exchange purposes. Floppy disk drives, with capacity of 1.44 MB, have been made obsolete: optical media are cheap and have vastly higher capacity to handle the large files used since the days of floppy discs, and the vast majority of computers and much consumer entertainment hardware have optical writers. USB flash drives, high-capacity, small, and inexpensive, are suitable where read/write capability is required.

Disc recording is restricted to storing files playable on consumer appliances ( films, music, etc.), relatively small volumes of data (e.g. a standard DVD holds 4.7 gigabytes, however, higher-capacity formats such as multi-layer Blu-ray Discs exist) for local use, and data for distribution, but only on a small scale; mass-producing large numbers of identical discs by pressing (replication) is cheaper and faster than individual recording (duplication).

Optical discs are used to back up relatively small volumes of data, but backing up of entire hard drives, which typically contain many hundreds of gigabytes or even multiple terabytes, is less practical. Large backups are often instead made on external hard drives, as their price has dropped to a level making this viable; in professional environments magnetic tape drives are also used.

Some optical drives also allow predictively scanning the surface of discs for errors and detecting poor recording quality.QPxTool - check the quality
List of supported devices by dosc quality scanning software ''QPxTool']

With an option in the optical disc authoring software, optical disc writers are able to simulate the writing process on CD-R, CD-RW, DVD-R and DVD-RW, which allows for testing such as observing the writing speeds and patterns (e.g. constant angular velocity, constant linear velocity and P-CAV and Z-CLV variants) with different writing speed settings and testing the highest capacity of an individual disc that would be achievable using overburning, without writing any data to the disc.

Few optical drives allow simulating a FAT32 flash drive from optical discs containing ISO9660/ Joliet and UDF file systems or audio tracks (simulated as .wav files),Video
"''Samsung ODD SE-S084D AV Connectivity"''
(published on September 14th 2010) for compatibility with most USB multimedia appliances.TSSTcorp SE-208AB portable external DVD drive — User manual: Using ''"AV"'' mode (FAT32 file system simulation)
(2011)

Key components

Form factors

Optical drives for computers come in two main form factors: '' half-height'' (also known as ''desktop drive'') and ''slim type'' (used in laptop computers and compact desktop computers). They exist as both internal and external variants.

''Half-height'' optical drives are around 4 centimetres tall, while ''slim type'' optical drives are around 1 cm tall.

''Half-height'' optical drives operate upwards of twice the speeds as ''slim type'' optical drives, because speeds on slim type optical drives are constrained to the physical limitations of the drive motor's rotation speed (around 5000 rpm) rather than the performance of the optical pickup system.

Because ''half-height'' demand much more electrical power and a voltage of 12 V DC, while ''slim'' optical drives run on 5 volts, external ''half height'' optical drives require separate external power input, while external ''slim type'' are usually able to operate entirely on power delivered through a computer's USB port. Half height drives are also faster than Slim drives due to this, since more power is required to spin the disc at higher speeds.

''Half-height'' optical drives hold discs in place from both sides while ''slim type'' optical drives fasten the disc from the bottom.

Half height drives fasten the disc using 2 spindles containing a magnet each, one under and one above the disc tray. The spindles may be lined with flocking or a texturized silicone material to exert friction on the disc, to keep it from slipping. The upper spindle is left slightly loose and is attracted to the lower spindle because of the magnets they have. When the tray is opened, a mechanism driven by the movement of the tray pulls the lower spindle away from the upper spindle and vice versa when the tray is closed. When the tray is closed, the lower spindle touches the inner circumference of the disc, and slightly raises the disc from the tray to the upper spindle, which is attracted to the magnet on the lower disc, clamping the disc in place. Only the lower spindle is motorized. Trays in half height drives often fully open and close using a motorized mechanism that can be pushed to close, controlled by the computer, or controlled using a button on the drive. Trays on half height and slim drives can also be locked by whatever program is using it, however it can still be ejected by inserting the end of a paper clip into an emergency eject hole on the front of the drive. Early CD players such as the Sony CDP-101 used a separate motorized mechanism to clamp the disc to the motorized spindle.

Slim drives use a special spindle with spring loaded specially shaped studs that radiate outwards, pressing against the inner edge of the disc. The user has to put uniform pressure onto the inner circumference of the disc to clamp it to the spindle and pull from the outer circumference while placing the thumb on the spindle to remove the disc, flexing it slightly in the process and returning to its normal shape after removal. The outer rim of the spindle may have a texturized silicone surface to exert friction keeping the disc from slipping. In slim drives most if not all components are on the disc tray, which pops out using a spring mechanism that can be controlled by the computer. These trays cannot close on their own; they have to be pushed until the tray reaches a stop.

Laser and optics

Optical pickup system

The most important part of an optical disc drive is an ''optical path'', which is inside a ''pickup head'' (''PUH''). The PUH is also known as a laser pickup, optical pickup, pickup, pickup assembly, laser assembly, laser optical assembly, optical pickup head/unit or optical assembly. It usually consists of a semiconductor laser diode, a lens for focusing the laser beam, and photodiodes for detecting the light reflected from the disc's surface.

Initially, CD-type lasers with a wavelength of 780 nm (within the infrared) were used. For DVDs, the wavelength was reduced to 650 nm (red color), and for Blu-ray Disc this was reduced even further to 405 nm (violet color).

Two main servomechanisms are used, the first to maintain the proper distance between lens and disc, to ensure the laser beam is focused as a small ''laser spot'' on the disc. The second servo moves the pickup head along the disc's radius, keeping the beam on the ''track'', a continuous spiral data path. Optical disc media are 'read' beginning at the inner radius to the outer edge.

Near the laser lens, optical drives are usually equipped with one to three tiny potentiometers (usually separate ones for CDs, DVDs, and usually a third one for Blu-ray Discs if supported by the drive) that can be turned using a fine screwdriver. The potentiometer is in a series circuit with the laser lens and can be used to manually increase and decrease the laser power for repair purposes.Video
''PS2 Potentiometer Adjustment - Disk Read Error Fix - YouTube''
(2015-06-06)

The laser diode used in DVD writers can have powers of up to 100 milliwatts, such high powers are used during writing. Some CD players have automatic gain control (AGC) to vary the power of the laser to ensure reliable playback of CD-RW discs.

Readability (the ability to read physically damaged or soiled discs) may vary among optical drives due to differences in optical pickup systems, firmwares, and damage patterns.

Read-only media

On factory-pressed ''read only media'' (ROM), during the manufacturing process the tracks are formed by pressing a thermoplastic resin into a nickel stamper that was made by plating a glass 'master' with raised 'bumps' on a flat surface, thus creating ''pits'' and ''lands'' in the plastic disk. Because the depth of the pits is approximately one-quarter to one-sixth of the laser's wavelength, the reflected beam's phase is shifted in relation to the incoming beam, causing mutual destructive interference and reducing the reflected beam's intensity. This is detected by photodiodes that create corresponding electrical signals.

Recordable media

An optical disk recorder encodes (also known as burning, since the dye layer is permanently burned) data onto a recordable CD-R, DVD-R, DVD+R, or BD-R disc (called a ''blank'') by selectively heating (burning) parts of an organic dye layer with a laser.

This changes the reflectivity of the dye, thereby creating marks that can be read like the pits and lands on pressed discs. For recordable discs, the process is permanent and the media can be written to only once. While the reading laser is usually not stronger than 5 mW, the writing laser is considerably more powerful. DVD lasers operate at voltages of around 2.5 volts.

The higher the writing speed, the less time a laser has to heat a point on the media, thus its power has to increase proportionally. DVD burners' lasers often peak at about 200 mW, either in continuous wave and pulses, although some have been driven up to 400 mW before the diode fails.

Rewriteable media

For rewritable CD-RW, DVD-RW, DVD+RW, DVD-RAM, or BD-RE media, the laser is used to melt a crystalline metal alloy in the recording layer of the disc. Depending on the amount of power applied, the substance may be allowed to melt back (change the phase back) into crystalline form or left in an amorphous form, enabling marks of varying reflectivity to be created.

Double-sided media

''Double-sided'' media may be used, but they are not easily accessed with a standard drive, as they must be physically turned over to access the data on the other side.

Dual layer media

''Double layer'' or ''dual layer'' (DL) media have two independent data layers separated by a semi-reflective layer. Both layers are accessible from the same side, but require the optics to change the laser's focus. Traditional ''single layer'' (SL) writable media are produced with a spiral groove molded in the protective polycarbonate layer (not in the data recording layer), to lead and synchronize the speed of recording head. Double-layered writable media have: a first polycarbonate layer with a (shallow) groove, a first data layer, a semi-reflective layer, a second (spacer) polycarbonate layer with another (deep) groove, and a second data layer. The first groove spiral usually starts on the inner edge and extends outwards, while the second groove start on the outer edge and extends inwards.

Photothermal printing

Some drives support Hewlett-Packard's LightScribe, or the alternative LabelFlash photothermal printing technology for labeling specially coated discs.

Multi beam drives

Zen Technology and Sony have developed drives that use several laser beams simultaneously to read discs and write to them at higher speeds than what would be possible with a single laser beam. The limitation with a single laser beam comes from wobbling of the disc that may occur at high rotational speeds; at 25,000 RPMs CDs become unreadable while Blu-rays cannot be written to beyond 5,000 RPMs. With a single laser beam, the only way to increase read and write speeds without reducing the pit length of the disc (which would allow for more pits and thus bits of data per revolution, but may require smaller wavelength light) is by increasing the rotational speed of the disc which reads more pits in less time, increasing data rate; hence why faster drives spin the disc at higher speeds. In addition, CDs at 27,500 RPMs (such as to read the inside of a CD at 52x) may explode causing extensive damage to the disc's surroundings, and poor quality or damaged discs may explode at lower speeds.

In Zen's system (developed in conjunction with Sanyo and licensed by Kenwood), a diffraction grating is used to split a laser beam into 7 beams, which are then focused into the disc; a central beam is used for focusing and tracking the groove of the disc leaving 6 remaining beams (3 on either side) that are spaced evenly to read 6 separate portions of the groove of the disc in parallel, effectively increasing read speeds at lower RPMs, reducing drive noise and
stress on the disc. The beams then reflect back from the disc, and are collimated and projected into a special photodiode array to be read. The first drives using the technology could read at 40x, later increasing to 52x and finally 72x. It uses a single optical pickup.

In Sony's system (used on their proprietary Optical Disc Archive system which is based on Archival Disc, itself based on Blu-ray) the drive has 4 optical pickups, two on each side of the disc, with each pickup having two lenses for a total of 8 lenses and laser beams. This allows for both sides of the disc to be read and written to at the same time, and for the contents of the disc to be verified during writing.

Rotational mechanism

File:Comparison disk storage.svg, Comparison of several forms of disk storage showing tracks (not-to-scale); green denotes start and red denotes end.
* Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.
File:CDRom.png, A half-height CD-ROM drive (without case)

The rotational mechanism in an optical drive differs considerably from that of a hard disk drive's, in that the latter keeps a constant angular velocity (CAV), in other words a constant number of revolutions per minute (RPM). With CAV, a higher throughput is generally achievable at the outer disc compared to the inner.

On the other hand, optical drives were developed with an assumption of achieving a constant throughput, in CD drives initially equal to 150 KiB/s. It was a feature important for streaming audio data that always tend to require a constant bit rate. But to ensure no disc capacity was wasted, a head had to transfer data at a maximum linear rate at all times too, without slowing on the outer rim of the disc. This led to optical drives—until recently—operating with a constant linear velocity (CLV). The spiral ''groove'' of the disc passed under its head at a constant speed. The implication of CLV, as opposed to CAV, is that disc angular velocity is no longer constant, and the spindle motor needed to be designed to vary its speed from between 200 RPM on the outer rim and 500 RPM on the inner, keeping the data rate constant.

Later CD drives kept the CLV paradigm, but evolved to achieve higher rotational speeds, popularly described in multiples of a base speed. As a result, a 4× CLV drive, for instance, would rotate at 800-2000 RPM, while transferring data steadily at 600 KiB/s, which is equal to 4 × 150 KiB/s.

For DVDs, base or 1× speed is 1.385 MB/s, equal to 1.32 MiB/s, approximately nine times faster than the CD base speed. For Blu-ray drives, base speed is 6.74 MB/s, equal to 6.43 MiB/s.

Because keeping a constant transfer rate for the whole disc is not so important in most contemporary CD uses, a pure CLV approach had to be abandoned to keep the rotational speed of the disc safely low while maximizing data rate. Some drives work in a partial CLV (PCLV) scheme, by switching from CLV to CAV only when a rotational limit is reached. But switching to CAV requires considerable changes in hardware design, so instead most drives use the zoned constant linear velocity (Z-CLV) scheme. This divides the disc into several zones, each having its own constant linear velocity. A Z-CLV recorder rated at "52×", for example, would write at 20× on the innermost zone and then progressively increase the speed in several discrete steps up to 52× at the outer rim. Without higher rotational speeds, increased read performance may be attainable by simultaneously reading more than one point of a data groove, also known as ''multi-beam'', but drives with such mechanisms are more expensive, less compatible, and very uncommon.

Limit

Both DVDs and CDs have been known to explode when damaged or spun at excessive speeds. This imposes a constraint on the maximum safe speeds (56× CAV for CDs or around 18×CAV in the case of DVDs) at which drives can operate.

The reading speeds of most half-height optical disc drives released since circa 2007 are limited to ×48 for CDs, ×16 for DVDs and ×12 (angular velocities) for Blu-ray Discs. Writing speeds on selected write-once media are higher.

Some optical drives additionally throttle the reading speed based on the contents of optical discs, such as max. 40× CAV (constant angular velocity) for the Digital Audio Extraction (''“DAE”'') of Audio CD tracks, 16× CAV for Video CD contents and even lower limitations on earlier models such as 4× CLV ( constant linear velocity) for Video CDs.Pioneer DVR-A06 brochure
(2003)

Loading mechanisms

Tray and slot loading

Current optical drives use either a ''tray-loading'' mechanism, where the disc is loaded onto a motorized (as utilized by half-height, ''"desktop"'' drives) tray, a manually operated tray (as utilized in laptop computers, also called ''slim type''), or a ''slot-loading'' mechanism, where the disc is slid into a slot and drawn in by motorized rollers. Slot-loading optical drives exist in both half-height (desktop) and slim type (laptop) form factors.Pioneer computer drive archive
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With both types of mechanisms, if a CD or DVD is left in the drive after the computer is turned off, the disc cannot be ejected using the normal eject mechanism of the drive. However, tray-loading drives account for this situation by providing a small hole where one can insert a paperclip to manually open the drive tray to retrieve the disc.

Slot-loading optical disc drives are prominently used in game consoles and vehicle audio units. Although allowing more convenient insertion, those have the disadvantages that they cannot usually accept the smaller 80 mm diameter discs (unless 80 mm optical disc adapter is used) or any non-standard sizes, usually have no emergency eject hole or eject button, and therefore have to be disassembled if the optical disc cannot be ejected normally. However, some slot-loading optical drives have been engineered to support miniature discs. The Nintendo Wii, because of backward compatibility with Nintendo GameCube games, and PlayStation 3 video game consoles are able to load both standard size DVDs and 80 mm discs in the same slot-loading drive. Its successor's slot drive however, the Wii U, lacks miniature disc compatibility.

There were also some early CD-ROM drives for desktop PCs in which its tray-loading mechanism will eject slightly and user has to pull out the tray manually to load a CD, similar to the tray ejecting method used in internal optical disc drives of modern laptops and modern external slim portable optical disc drives. Like the top-loading mechanism, they have spring-loaded ball bearings on the spindle.

Top-load

A small number of drive models, mostly compact portable units, have a ''top-loading'' mechanism where the drive lid is manually opened upwards and the disc is placed directly onto the spindleLiteOn eTAU108 - DVD±RW (±R DL) / DVD-RAM drive - Hi-Speed USB Series Specification sheet and picture
- CNet.com, 2009; accessed July 11th 2020. (for example, all PlayStation One consoles, PlayStation 2 Slim, PlayStation 3 Super Slim, Nintendo GameCube consoles, Nintendo Wii Mini, most portable CD players, and some standalone CD recorders feature top-loading drives). These sometimes have the advantage of using spring-loaded ball bearings to hold the disc in place, minimizing damage to the disc if the drive is moved while it is spun up.

Unlike tray and slot loading mechanisms by default, top-load optical drives can be opened without being connected to power.

Cartridge load

Some early CD-ROM drives used a mechanism where CDs had to be inserted into special cartridges or caddies, somewhat similar in appearance to a 3.5 inch micro floppy diskette. This was intended to protect the disc from accidental damage by enclosing it in a tougher plastic casing, but did not gain wide acceptance due to the additional cost and compatibility concerns—such drives would also inconveniently require "bare" discs to be manually inserted into an openable caddy before use. Ultra Density Optical (''UDO''), Magneto-optical drives, Universal Media Disc (''UMD''), DataPlay, Professional Disc, MiniDisc, Optical Disc Archive as well as early DVD-RAM and Blu-ray discs use optical disc cartridges.

Computer interfaces

All optical disc-drives use the SCSI-protocol on a command bus level, and initial systems used either a fully featured SCSI bus or as these were some what cost-prohibitive to sell to consumer applications, a proprietary cost-reduced version of the bus. This is because conventional ATA-standards at the time did not support, or have any provisions for any sort of removable media or hot-plugging of disk drives. Most modern internal drives for personal computers, servers, and workstations are designed to fit in a standard -inch (also written as 5.25 inch) drive bay and connect to their host via an ATA or SATA bus interface, but communicate using the SCSI protocol commands on software level as per the ATA Package Interface standard developed for making Parallel ATA/IDE interfaces compatible with removable media. Some devices may support vendor-specific commands such as recording density (" GigaRec"), laser power setting (" VariRec"), ability to manually hard-limit rotation speed in a way that overrides the universal speed setting (separately for reading and writing), and adjusting the lens and tray movement speeds where a lower setting reduces noise, as implmenented on some Plextor drives, as well as the ability to force overspeed burning, meaning beyond speed recommended for the media type, for testing purposes, as implemented on some Lite-On drives. Additionally, there may be digital and analog outputs for audio. The outputs may be connected via a header cable to the sound card or the motherboard or to headphones or an external speaker with a