Editing Optical disc drive (section)

== 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 [[Desktop computer#Compact|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&nbsp;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 [[#Rotational_mechanism|drive motor's rotation speed]] (around 5000[[rotations per minute|rpm]]<ref name="hughnews-BD">{{cite web |title=BluRay — Recording and reading speed |url=http://www.hughsnews.ca/faqs/authoritative-blu-ray-disc-bd-faq/8-recording-and-reading-speed |website=www.hughsnews.ca |access-date=11 August 2020 |quote=At this early stage anticipating anything is merely speculation but it's possible to make some informed predictions. From a practical perspective, spinning an optical disc at 10,000 RPM has long proven the realistic limit for half-height drives and 5,000 RPM for slim-types.}}</ref>) rather than the performance of the [[#Optical_pickup_system|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]]. (In some slim drives, two USB connectors are required, each supplying power, but only one the data.) 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. 
<ref name=Pioneer-Archive />

=== Laser and optics ===

==== Optical pickup system ====
[[File:CD Player focusing lens assembly.jpg|thumb|Pickup head]]
[[File:LG DVD GDR-8164B 07 laser read head.jpg|thumb|Optical pickup unit with two visible [[potentiometer]]s]]
[[File:Philips 1 beam tracking Laser Optical Assembly.jpg|thumb|Pickup head, side view]]
[[File:Detail of DVD-RW optics.png|thumb|Optical path]]
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.<ref name=dvd>{{Cite book |first1=Jim H. |last1=Taylor |first2=Mark R. |last2=Johnson |first3=Charles G. |last3=Crawford |title=DVD Demystified |publisher=McGraw-Hill Professional | year=2006 |url=https://books.google.com/books?id=ikxuL2aX9cAC&pg=PT229 |pages=7–8 |isbn=0-07-142396-6}}</ref> It usually consists of a semiconductor [[laser diode]], a [[lens (optics)|lens]] for focusing the laser beam, and [[photodiode]]s for detecting the light reflected from the disc's surface.<ref name=cd>{{Cite book |first=Sorin G. |last=Stan |title=The CD-ROM Drive: A Brief System Description |publisher=Springer |year=1998 |url=https://books.google.com/books?id=Gs3pdRb83VcC&pg=PA14 |page=13 |isbn=0-7923-8167-X}}</ref>

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

Two main [[servomechanism]]s 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 [[potentiometer]]s (usually separate ones for [[compact disc|CD]]s, [[DVD]]s, and usually a third one for [[Blu-ray Disc]]s if supported by the drive<ref>{{cite web |title=Tearing Down A PS3 Blu Ray Drive |url=https://hackaday.com/2019/11/12/tearing-down-a-ps3-blu-ray-drive/ |website=Hackaday |access-date=31 July 2020 |date=12 November 2019}}</ref>) 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 [[milliwatt]]s, such high powers are used during writing.<ref>{{cite web |title=100mW-Laserdioden aus 16x-DVD-Brennern |url=https://www.mikrocontroller.net/attachment/12346/Laserdiode8.pdf |website=mikrocontroller.net |access-date=11 August 2020 |language=de}}</ref> Some CD players have [[automatic gain control]] (AGC) to vary the power of the laser to ensure reliable playback of CD-RW discs.<ref name="auto"/><ref>{{Cite web|url=https://users.cs.cf.ac.uk/Dave.Marshall/Multimedia/node134.html|title=Compatibility of DVD}}</ref>

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.<ref>{{cite web |title=5. Conditions That Affect CDs and DVDs • CLIR |url=https://www.clir.org/pubs/reports/pub121/sec5/ |website=CLIR}}</ref>

==== Read-only media ====
{{Unreferenced section|date=December 2024}}

[[File:Optical Disk Drive Photodetector.jpg|alt=The optical sensor out of a CD/DVD drive|thumb|The optical sensor out of a CD/DVD drive. The two larger rectangles are the photodiodes for pits, the inner one for land. This one also includes amplification and minor processing.]]
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 (wave propagation)|interference]] and reducing the reflected beam's intensity. This is detected by photodiodes that create corresponding electrical signals.

==== Recordable media ====
{{missing information|section|laser wattages for reading and writing of individual media types|date=August 2020}}
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.{{Citation needed|date=February 2007}}

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 [[Watt|mW]], the writing laser is considerably more powerful.<ref>{{cite web |title=Laser diodes from CD-RW drives can cut and burn! |url=http://danyk.cz/laser_en.html |website=danyk.cz |access-date=11 August 2020}}</ref> DVD lasers operate at voltages of around 2.5 volts.<ref>{{cite web |title=Powerful laser diodes from DVD-RW drive |url=http://danyk.cz/laser3_en.html |website=danyk.cz |language=en}}</ref>

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&nbsp;mW, either in continuous wave and pulses, although some have been driven up to 400&nbsp;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 [[crystal]]line 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 solid|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.<ref>{{Cite web|url=https://i.publiclab.org/system/images/photos/000/008/589/original/doublelayer1.gif|title=Cross Section of DVD+R DL Optical Media}}</ref><ref>{{Cite web|url=http://www.windowsusers.org/images/Dvd/R_dl.jpg|title=Cross Section of DVD+R DL Optical Media}}</ref>

==== Photothermal printing ====
Some drives support [[HP Inc.|Hewlett-Packard]]'s [[LightScribe]], or the alternative [[Labelflash|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<ref name="auto">{{Cite web|url=https://cdrfaq.org/faq05.html|title=CD-Recordable FAQ - section 5|website=cdrfaq.org}}</ref> while Blu-rays cannot be written to beyond 5,000 RPMs.<ref>{{Cite web |date=January 2018 |title=White Paper Blu-ray Disc™ Format General |url=http://www.blu-raydisc.com/Assets/Downloadablefile/White_Paper_General_5th_20180216.pdf |archive-url=https://web.archive.org/web/20211028160330/http://www.blu-raydisc.com/Assets/Downloadablefile/White_Paper_General_5th_20180216.pdf |archive-date=Oct 28, 2021 |website=blu-raydisc.com |edition=5th}}</ref> 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.<ref>{{Cite web|url=https://www.smh.com.au/technology/life-in-the-fast-lane-can-be-a-disc-shattering-experience-20021209-gdfxwp.html|title=Life in the fast lane can be a disc-shattering experience|date=December 9, 2002|website=The Sydney Morning Herald}}</ref><ref name="auto"/>

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.<ref name="Anandtech-Multibeam"/><ref>{{Cite web|url=https://hothardware.com/reviews/kenwoods-72x-true-x-cdrom-drive|title=Kenwood's 72X True X CDROM Drive |date=December 15, 2001|website=HotHardware}}</ref><ref name="CDRinfo-MultiBeam"/><ref>{{Cite web|url=https://gcn.com/articles/2000/08/07/kenwoods-72x-cd-cant-keep-pace-with-24x-cdrw.aspx|title=Kenwood's 72X CD can't keep pace with 24X CD-RW -|date=August 7, 2000|website=GCN}}</ref><ref>{{Cite web|url=https://www.targetpc.com/hardware/cd-rom/kenwood72x/|title=Target PC :: Kenwood 72X IDE CD-ROM|website=www.targetpc.com}}</ref><ref>{{Cite web|url=https://www.theregister.com/1999/11/08/kenwood_launches_72x_cd_unit/|title=Kenwood launches 72x CD unit|website=www.theregister.com}}</ref>

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.<ref>{{Cite web |title=Optical Disc Archive Generation 2 White Paper |url=https://pro.sony/s3/cms-static-content/file/49/1237494482649.pdf |access-date=2024-11-13 |website=Sony Professional}}</ref>

=== Rotational mechanism ===
{{Further|Disk drive performance characteristics}}
<gallery perrow="1" style="float:left">
File:Comparison disk storage.svg|Comparison of several forms of disk storage showing tracks (not-to-scale); green denotes start and red denotes end.<br ><nowiki>*</nowiki> 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)
</gallery>

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&nbsp;RPM on the outer rim and 500&nbsp;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&nbsp;KiB/s, which is equal to 4 × 150&nbsp;KiB/s.

For DVDs, base or 1× speed is 1.385&nbsp;MB/s, equal to 1.32&nbsp;MiB/s, approximately nine times faster than the CD base speed. For Blu-ray drives, base speed is 6.74&nbsp;MB/s, equal to 6.43&nbsp;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'',<ref name="pcstats-kenwood">{{Cite book | last = Page | first = M. | title = Kenwood 72× CD-ROM Review | page = 2 | url=http://www.pcstats.com/articleview.cfm?articleid=339&page=2 | archive-url=https://web.archive.org/web/20120301062026/https://www.pcstats.com/articleview.cfm?articleid=339&page=2 | archive-date=2012-03-01 | access-date = 2007-10-08}}</ref> but drives with such mechanisms are more expensive, less compatible, and very uncommon.

==== Limit ====
In the past, CD-ROMs have exploded when damaged or spun at excessive [[CD-ROM#Speed table|speeds]]. This imposes a constraint on the maximum safe speeds (56× [[constant angular velocity|CAV]] for CDs or around 18×CAV in the case of DVDs) at which drives can operate. [[Lite-On]] estimates the incidence of exploding CDs at one or two discs in 10,000.<ref name="NYT">{{cite news |title=Spinning out of control: Risk of CD explosion |first=Brad |last=Spurgeon |newspaper=[[The New York Times]] |date=December 11, 2004 |url=https://www.nytimes.com/2004/12/11/business/worldbusiness/11iht-ptcd_ed3_.html? |archive-url=https://web.archive.org/web/20140325152833/http://www.nytimes.com/2004/12/11/business/worldbusiness/11iht-ptcd_ed3_.html |archive-date=March 25, 2014 |url-status=dead }}</ref> 

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 ([[constant angular velocity|angular velocities]]) for Blu-ray Discs, which are physically similar rotation speeds that surround 10,000 rpm despite of the differing numbers.{{efn|1=The [[constant angular velocity|angular disc speeds]] of ×48 on CDs, ×16 on DVDs and ×12 on Blu-ray Discs refer to that equivalent [[constant linear velocity|linear velocity]] required for this multiple of [[CD and DVD writing speed#CD, DVD and Blu-ray writing speeds|the respective original speeds]], if accessed at the outermost disc edge, and amounts to similar [[CD-ROM#Speed table|physical rotation speeds]].}} Writing speeds on selected [[Write once read many|write-once]] media are higher.<ref name="Pioneer-Archive" /><ref name="HL-DT-ST-Discontinued">{{Cite web|url=https://www.lg.com/us/burners-drives/discontinued|archive-url=https://archive.today/20200711193519/https://www.lg.com/us/burners-drives/discontinued|archive-date=2020-07-11|title=View All Discontinued LG Burners & Drives|website=LG USA|access-date=2020-07-11|url-status=live}}</ref><ref name="TSST-Manuals">{{Cite web|url=http://www.tsstodd.com/manual-2/|title=Manual}}</ref>

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,<ref name="HL-DT-ST-Discontinued" /> 16× CAV for [[Video CD]] contents<ref name="TSST-Manuals" /> and even lower limitations on earlier models such as 4× CLV ([[constant linear velocity]]) for [[Video CD]]s.<ref name="Pioneer-DVR-107">{{cite web |title=DVR-107D, DVR-107BK General Specifications |url=https://www.pioneerelectronics.com/pio/pe/images/portal/cit_3424/63510151DVRx07_GSpec.pdf |website=[[Pioneer Electronics]] USA |access-date=31 July 2020 |date=2004}}</ref><ref name="DVR-A06-brochure">[https://www.pioneerelectronics.com/pio/pe/images/portal/cit_3424/2370275DVR-A06_brochure.pdf Pioneer DVR-A06 brochure] (2003)</ref>

A 2003 [[MythBusters]] episode erroneously claims that a CD spinning at "52× speed" spins at 30,000 rotations per minute (rpm).<ref>{{cite AV media |url=https://www.youtube.com/watch?v=5msQv86NRWE&t=40m39s |title=Can A Cell Phone Destroy A Gas Station!? &#x7c; MythBusters &#x7c; Season 1 Episode 2 &#x7c; Full Episode |date=2024-12-26 |access-date=2024-12-17 }} (at 40 minutes and 39 seconds) (originally aired in 2003) (mirror: {{cite AV media |url=https://www.youtube.com/watch?v=3wKAQw0yU2U&t=42m37s |title=Mysthbusters season 1 episode 02 - Cell Phone Destroys Gas Station |date=2015-07-25 |access-date=2024-12-17 }})</ref> This miscalculation is caused by assuming a '''linear''' velocity of 52× at the inner edge of the data area of the disc, which would indeed reach dangerous speeds in excess of 25,000 rpm, therefore optical drives never spin discs at such speeds. In actuality, a CD speed of "52×" are approximately 10,000 rpm (see [[CD-ROM#Speed_table|table]], different for DVD and Blu-ray)<!--editor note: I am using approximation here because I am not sure whether the numbers from the source of the table apply equally to every CD, given that CDs with varying data densities exist. I also couldn't confirm yet whether the data on every CD starts on the exact same physical distance from the center of the disc. --CDVDBD, February 9, 2025. -->, given that drives are advertised with their [[Constant Angular Velocity|'''angular''' velocities]]. The angular velocity is the measured as the [[Constant Linear Velocity|linear velocity]] at the outermost edge of the disc, where the linear velocity (and accordingly the data transfer rate) is roughly 2.5 times higher than at the innermost edge of the data area.<ref name="1xCD-ROM">{{Cite web|url=https://encyclopedia2.thefreedictionary.com/1x+CD-ROM|title=1x CD-ROM|website=encyclopedia2.thefreedictionary.com}}</ref><ref>{{Cite book|title=Computer Architecture and Organization Design Principles and Applications|year=2004|publisher=Tata McGraw-Hill|page=547|isbn=978-0070532366}}</ref>
{{Clear}}

=== Loading mechanisms ===
<!-- File gone: [[File:Plextor PX-W8432Ti - opening tray manually.webm|thumb|Opening the tray of a CD-RW manually with the help of a paper clip]] -->

==== Tray and slot loading ====
Current optical drives use either a ''tray-loading'' mechanism, where the disc is loaded onto a motorized tray (as utilized by [[half-height]], ''"desktop"'' drives), 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.<ref name="Pioneer-Archive">[https://www.pioneerelectronics.com/PUSA/Computer/ch.Computer+Drives.Archived Pioneer computer drive archive]</ref>

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.<ref>{{cite web|url=https://tenpire.com/guide-for-different-types-of-optical-drives/ |title=Guide For Different Types Of Optical Drives |publisher=Tenpire |access-date=2019-06-12}}</ref>

Slot-loading optical disc drives are prominently used in [[game console]]s and [[vehicle audio]] units. Although allowing more convenient insertion, those have the disadvantages that they cannot usually accept the smaller [[miniDVD|80 mm diameter discs]] (unless 80&nbsp;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 [[GameCube]] games,<ref>{{cite web|url=https://www.nintendo.com/consumer/systems/wii/en_na/gi_system.jsp?menu=console&submenu=rvl-gi-sys-diff |title=&#124; Wii - General Information: System & Accessories |publisher=Nintendo |access-date=2013-01-07}}</ref><ref name="GCN-disc-in-Wii">{{Cite web|url=https://www.youtube.com/watch?v=i8iYBcqJqyU |archive-url=https://ghostarchive.org/varchive/youtube/20211212/i8iYBcqJqyU| archive-date=2021-12-12 |url-status=live|title=Video: ''"What Happens When you put a GameCube disc into a Nintendo Wii"''|website=[[YouTube]]|date=23 May 2018 }}{{cbignore}}</ref> and [[PlayStation 3]]<ref>{{Cite book | title = PlayStation 3 Instruction Manual | page = 50 | url = https://www.playstation.com/content/dam/global_pdc/en/corporate/support/manuals/ps3-docs/CECH-2001A_2001B-2.85_2_EN_ES_AMER_IM.pdf | access-date = 2023-06-07}}</ref> video game consoles are able to load both standard size DVDs and 80&nbsp;mm discs in the same slot-loading drive. Its successor's slot drive however, the [[Wii U]], lacks miniature disc compatibility.<ref name="WiiU-GCN">{{Cite web|url=https://en-americas-support.nintendo.com/app/answers/detail/a_id/1158/~/what-discs-are-compatible-with-the-wii-u?|title=Nintendo Support: What Discs Are Compatible with the Wii U?|website=en-americas-support.nintendo.com}}</ref>

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{{citation needed|date=July 2020}}, 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 spindle<ref>{{Cite book | publisher = TEAC | title = CD-210PU USB interface portable CD-ROM drive | url=http://www.teac.co.jp/dspd/product/optical/cd-210pu.html | access-date = 2007-10-08}}</ref><ref name="eTAU108">[https://www.cnet.com/products/liteon-etau108-dvdrw-r-dl-dvd-ram-drive-hi-speed-usb-series/ LiteOn eTAU108 - DVD±RW (±R DL) / DVD-RAM drive - Hi-Speed USB Series Specification sheet and picture] - CNet.com, 2009; accessed July 11th 2020.</ref> (for example, all PlayStation One consoles, PlayStation 2 Slim, PlayStation 3 Super Slim, GameCube consoles, Nintendo Wii Mini, most [[portable CD player]]s, 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 [[Caddy (hardware)|caddies]], somewhat similar in appearance to a [[Floppy disk#3 1⁄2-inch disk|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 drive]]s, [[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 ===
[[Image:Sony DDU1621 backside 20071019.jpg|right|thumb|[[Digital audio]] output, [[analog audio]] output, and [[parallel ATA]] interface]]
All optical disc-drives use the [[SCSI]]-protocol on a command bus level, and initial systems used either a fully featured SCSI [[bus (computing)|bus]] or as these were somewhat cost-prohibitive to sell to consumer applications, a proprietary cost-reduced version of the bus. This is because conventional [[Parallel ATA|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 computer]]s, [[Server (computing)|server]]s, and [[workstation]]s are designed to fit in a standard {{frac|5|1|4}}-inch (also written as 5.25 inch) [[drive bay]] and connect to their host via an [[Advanced Technology Attachment|ATA]] or [[SATA]] bus interface, but communicate using the SCSI protocol commands on software level as per the [[ATA Packet Interface|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 (audio)|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.<ref>{{cite web |title=cdvdcontrol • man page |url=https://helpmanual.io/man1/cdvdcontrol/ |website=helpmanual.io |date=2014-02-26}}</ref><ref>{{cite book |title=Maximum PC – Bear Year |date=December 2002 |page=30,80 |url=https://books.google.com/books?id=zQEAAAAAMBAJ&q=plextor+plexwriter+48/24/48&pg=PA80}}</ref><ref>[http://cdrtools.sourceforge.net/private/man/cdrecord/cdrecord.1.html Manpage for cdrecord.1]</ref><ref>{{cite web |title=Lite-On iHAS324 - Printer Friendly version |url=https://www.cdrinfo.com/Sections/Reviews/Print.aspx?ArticleId=25680 |website=CDR info |access-date=14 August 2021 |date=2009-07-14 |quote=SmartWrite can overspeed certain 16X DVD±R media to a maximum of 24X }}</ref> 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 [[3.5 mm jack|3.5mm AUX plug cable]] that many early optical drives are equipped with.<ref name="NEC" /><ref name="3.5mm">{{Cite web|url=http://danyk.cz/laser_01.jpg|title=Photo of early CD-ROM drives with Audio CD control buttons and 3.5mm headphone plug}}</ref> At one time, computer software resembling [[CD player]]s controlled playback of the CD.<ref>{{cite web |title=cdtool |url=http://hinterhof.net/cdtool/ |website=hinterhof.net |access-date=25 July 2020 |date=2006-08-09}}</ref><ref>{{cite web |title=cdtool(1) [debian man page] |url=https://www.unix.com/man-page/debian/1/cdtool/ |website=www.unix.com |language=en |date=2004-07-29}}</ref> Today the information is [[CD ripping|extracted]] from the disc as digital data, to be played back or converted to other file formats.

Some early optical drives have dedicated buttons for CD playback controls on their front panel, allowing them to act as a standalone [[compact disc player]].<ref name="NEC">{{Cite web|url=https://www.electromyne.com/images/large/131349a.jpg|title=Picture of the front panel of a NEC CDR-502 with standalone CD playback control buttons}}</ref>

External drives were popular in the beginning, because the drives often required complex electronics to institute, rivaling in complexity the Host computer system itself. External drives using [[SCSI]], [[Parallel port]], [[USB]] and [[FireWire]] interfaces exist, most modern drives being [[USB]]. Some portable versions for laptops power themselves from batteries or directly from their interface bus.

Drives with a [[SCSI]] interface were originally the only system interface available, but they never became popular in the price sensitive low-end consumer market which constituted majority of the demand. They were less common and tended to be more expensive, because of the cost of their interface chipsets, more complex SCSI connectors, and small volume of sales in comparison to proprietary cost-reduced applications, but most importantly because most consumer market computer systems did not have any sort of SCSI interface in them the market for them was small. However, support for multitude of various cost-reduced proprietary optical drive bus standards were usually embedded with sound cards which were often bundled with the optical drives themselves in the early years. Some sound card and optical drive bundles even featured a full SCSI bus. Modern IDE/ATAPI compliant Parallel ATA and Serial ATA drive control chipsets and their interface technology is more complex to manufacture than a traditional 8bit 50&nbsp;Mhz SCSI drive interface, because they feature properties of both the SCSI and ATA bus, but are cheaper to make overall due to economies of scale.

When the optical disc drive was first developed, it was not easy to add to computer systems. Some computers such as the IBM PS/2 were standardizing on the {{frac|3|1|2}}-inch floppy and {{frac|3|1|2}}-inch hard disk and did not include a place for a large internal device. Also IBM PCs and clones at first only included a single (parallel) [[Parallel ATA|ATA]] drive interface, which by the time the CD-ROM was introduced, was already being used to support two hard drives and were completely incapable of supporting removable media, a drive falling off or being removed from the bus while the system was live, would cause an unrecoverable error and crash the entire system. Early consumer grade laptops simply had no built-in high-speed interface for supporting an external storage device. High-end workstation systems and laptops featured a SCSI interface which had a standard for externally connected devices.

[[Image:HP C4381A CD-Writer Plus 7200 Series-4077.jpg|right|thumb|''[[Hewlett-Packard|HP]] C4381A CD-Writer Plus 7200 Series'' (1998), showing parallel ports to connect between a printer and the computer]] This was solved through several techniques:

* Early [[sound cards]] could include a CD-ROM drive interface. Initially, such interfaces were proprietary to each CD-ROM manufacturer. A sound card could often have two or three different interfaces which are able to communicate with the CD-ROM drive.
* A method for using the [[parallel port]] to use with external drives was developed at some point. This interface was traditionally used to connect a printer, but despite popular myth it is not its only use and various different external auxiliary devices exist for the IEEE-1278 bus, including but not limited to tape backup drives etc. This was slow but an option for low-to-midrange laptops without integrated or PCMCIA extension bus connected SCSI.
* A [[PCMCIA]] optical drive interface was also developed for laptops.
* A SCSI card could be installed in desktop PCs to cater for an external SCSI drive enclosure or to run internally mounted SCSI Hard disk drives and optical drives, though SCSI was typically somewhat more expensive than other options, with some OEMs charging a premium for it.

Due to lack of [[Asynchrony (computer programming)|asynchrony]] in existing implementations, an optical drive encountering damaged sectors may cause computer programs trying to access the drives, such as [[Windows Explorer]], to [[Hang (computing)|lock up]].

=== SCSI configuration ===
Drive models may support adjustment of behavioural parameters for performance optimization and testing purposes, such as the read retry count (<code>RRC</code>), write retry count (<code>WRC</code>), and the option to deactivate error correction (<code>DCR</code>). For example, the read retry count specifies how often the drive should attempt reading a damaged sector. A higher value may increase the chance of successfully reading individual damaged sectors, but at the expense of responsiveness, since it adds delays during which the device seems unresponsive to the computer.

The <code>sdparm</code> command-line utility allows manually controlling such parameters. For example, <code>sdparm --set RRC=10 /dev/sr0</code> sets the read retry count to 10 for the optical drive [[device file]] "sr0", and <code>sdparm --all /dev/sr0</code> lists all code pages. The values may be interpreted varyingly among drive models or vendors.<ref>{{cite web |title=Linux sdparm utility |url=https://sg.danny.cz/sg/sdparm.html |website=sg.danny.cz |access-date=14 March 2022}}</ref><ref>{{cite web |title=SCSI-2 Spec - Direct-access devices |url=http://www.staff.uni-mainz.de/tacke/scsi/SCSI2-09.html |website=www.staff.uni-mainz.de |access-date=14 March 2022}}</ref>

=== Internal mechanism of a drive ===
[[File:Dismdvd.jpg|thumb|right|Internal mechanism of a DVD-ROM Drive. See text for details.]]

The optical drives in the photos are shown right side up; the disc would sit on top of them. The laser and optical system scans the underside of the disc.

With reference to the top photo, just to the right of image center is the disc motor, a metal cylinder, with a gray centering hub and black rubber drive ring on top. There is a disc-shaped round clamp, loosely held inside the cover and free to rotate; it's not in the photo. After the disc tray stops moving inward, as the motor and its attached parts rise, a magnet near the top of the rotating assembly contacts and strongly attracts the clamp to hold and center the disc. This motor is an "outrunner"-style [[Brushless DC electric motor|brushless DC motor]] which has an external rotor – every visible part of it spins.

Two parallel guide rods that run between upper left and lower right in the photo carry the "sled", the moving optical read-write head. As shown, this "sled" is close to, or at the position where it reads or writes at the edge of the disc. To move the "sled" during continuous read or write operations, a [[stepper motor]] rotates a leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the short gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew is the rod with evenly-spaced darker details; these are the helical grooves that engage a pin on the "sled".

In contrast, the mechanism shown in the second photo, which comes from a cheaply made DVD player, uses less accurate and less efficient brushed [[DC motor]]s to both move the sled and spin the disc. Some older drives use a DC motor to move the sled, but also have a magnetic [[rotary encoder]] to keep track of the position. Most drives in computers use stepper motors.

The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise from residual imbalance when running fast. The soft shock mount grommets are just below the brass-colored screws at the four corners (the left one is obscured).

In the third photo, the components under the cover of the lens mechanism are visible. The two permanent magnets on either side of the lens holder as well as the coils that move the lens can be seen. This allows the lens to be moved up, down, forwards, and backwards to stabilize the focus of the beam.

In the fourth photo, the inside of the optics package can be seen. Note that since this is a CD-ROM drive, there is only one laser, which is the black component mounted to the bottom left of the assembly. Just above the laser are the first focusing lens and prism that direct the beam at the disc. The tall, thin object in the center is a half-silvered [[mirror]] that splits the laser beam in multiple directions. To the bottom right of the mirror is the main [[photodiode]] that senses the beam reflected off the disc. Above the main photodiode is a second photodiode that is used to sense and regulate the power of the laser.

The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "[[flexible circuit]]s" that connect everything to the electronics (which is not shown).