Optical disc 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, while other drives can both read and record. Those drives are called burners or writers since they physically burn the data onto the discs. Compact discs, DVDs, and Blu-ray discs are common types of optical media which can be read and recorded by such drives.
Although most laptop manufacturers no longer have optical drives bundled with their products, external drives are still available for purchase separately.
Drive types
Some drives can only read data whereas others can both read data and write data to writable discs. Drives which can read but not write data are "-ROM" drives, even if they can read from writable formats such as "-R" and "-RW". Some drives have mixed read and write capabilities, such as the TSST TS-LB23, which can only read Blu-ray discs but read and write CDs and DVDs., most of the optical disc drives on the market are DVD and Blu-ray drives, which read from and record to those formats, along with having backward compatibility with audio CD, CD-R/-RW, and CD-ROM discs.
Compact disc-only drives are no longer manufactured outside of audio devices and are obsolete in the consumer market for internal/external drives. Read-only DVD-ROM and BD-ROM drives are also manufactured, but are less commonly found in the consumer market, being mainly limited to media devices such as game consoles and disc media players. Most consumer-grade laptop computers used to come with built-in optical drives. Some laptop computers used modular systems. Throughout the 2010s, they ceased to come with built-in optical disc drives in order to reduce costs and make them lighter and thinner, 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, and video game consoles. As of 2017, the PlayStation and Xbox consoles are the only home video game consoles that are currently using optical discs as its primary storage format, as the Wii U's successor, the Nintendo Switch, began using game cartridges, while the PlayStation Portable is the only handheld console to use optical discs, using Sony's proprietary UMD format. 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 disks, 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, relatively small volumes of data for local use, and data for distribution, but only on a small scale; mass-producing large numbers of identical discs by pressing is cheaper and faster than individual recording.
To support 8 centimetre diameter discs, drives with mechanical tray loading have an indentation in the tray. It can however only be used in horizontal operation.
Slot loading drives, frequently used in game consoles and car radios, might be able to accept 8 centimetre discs and center the disc automatically.
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.
The drive reduces the rotation speed of discs when encountering damage, since a lower reading speed improves readability of damaged media.
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 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, for compatibility with most USB multimedia appliances.
Key components
Form factors
Optical drives for computers come in two main form factors: half-height and slim type. 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] 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.
The top surface of the metal chassis of half-height drives can be shaped in a way that reduces disc rotation noise and creates an airflow that stabilizes the disc. For this reason the top surface of many drives have indents instead of being completely flat. Slim-type drives lack them due to a lack of physical room and don't need them given that they spin discs at much lower speeds.
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. 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 were used. For DVDs, the wavelength was reduced to 650 nm, and for Blu-ray Disc this was reduced even further to 405 nm.
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 that can be turned using a fine screwdriver. The potentiometer is in a series circuit with the laser lens.
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 to vary the power of the laser to ensure reliable playback of CD-RW discs.
Readability may vary among optical drives due to differences in optical pickup systems, firmwares, and damage patterns.