In computing, the optical disc drive (ODD ) is a disk drive that uses laser light or electromagnetic waves inside or near the visible light spectrum as part of the process of reading or writing data to or from an optical disc. Some drives can only read from certain discs, but recent drives can read and record, also called burners or authors. Compact discs, DVDs, and Blu-ray discs are common types of optical media that the drive can read and record. Non-manufactured optical disk drives include CD-ROM drives, CD writer drives, combo drives (CD-RW/DVD-ROM), and DVD writer drives that support certain recordable and rewritable DVD formats (such as DVD-R (W)) only, DVD R (W) only, DVD-RAM only, and all DVD formats except DVD-R DL). By 2015, DVD writer drives supporting all recordable and rewritable DVD formats are the most common for desktop and laptop PCs. There are also DVD-ROM drives, BD-ROM drives, Blu-ray Disc combo drives (BD-ROM/DVDÃ, Â ± RW/CD-RW), and Blu-ray Disc writer drives.
The optical disk drive is an integral part of standalone equipment 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 and Sony PlayStation 3, and certain portable video game consoles, such as the Sony PlayStation Portable. They are also very commonly used in computers to read software and consumer media distributed on disk, and to record disks for archival and data exchange purposes. Floppy disk drives, with a capacity of 1.44 MB, have been made obsolete: cheap optical media and have a much higher capacity to handle large files used since the floppy time, and most computers and many consumer entertainment devices have optical authors. USB flash drive, high capacity, small, and cheap, suitable where the ability to read/write is required.
Disk recording is limited to storing playable files on consumer equipment (movies, music, etc.), relatively small data volumes (eg standard DVDs have 4.7 gigabytes) for local use, and data for distribution, but only on a small scale; mass-producing mass of identical disks is cheaper and faster than individual recordings.
Optical discs are used to back up relatively small volumes of data, but reserve the entire hard drive, which in 2015 typically contains hundreds of gigabytes or even some terabytes, is less practical. Large backups are often made on external hard drives, as the price has dropped to levels that make this feasible; in a professional environment magnetic tape drive is also used.
Video Optical disc drive
History
The first laser disc, shown in 1972, was a 12-inch LasVision video disk. The video signal is stored as an analog format such as a video cassette. The first digitally recorded digital disc is a 5-inch (compact disc) audio CD in read-only format created by Sony and Philips in 1975.
The first deleted optical disk drive was announced in 1983, by Matsushita (Panasonic), Sony, and Kokusai Denshin Denwa (KDDI). Sony finally released the first 5.25 inch optical disk drive that could be erased and rewritten in 1987, with two-sided discs capable of holding 325 MB per side.
The CD-ROM format developed by Sony and Denon, was introduced in 1984, as an extension of Compact Disc Digital Audio and was adapted to store all forms of digital data. The CD-ROM format has a storage capacity of 650 MB. Also in 1984, Sony introduced the LaserDisc data storage format, with a larger data capacity of 3.28 GB. The DVD format, developed by Panasonic, Sony, and Toshiba, was released in 1995, and is capable of holding 4.7 GB per layer.
The first Blu-Ray prototype was unveiled by Sony in October 2000, and the first commercial tape recorder was released to the market on April 10, 2003. In January 2005, TDK announced that it has developed an ultra-hardened yet very thin ("Durabis") polymer layer for Blu-ray discs; this is a significant technical advancement because of the better protection desired for the consumer market to protect the bare discs against scratches and damage compared to DVDs. Technically Blu-ray Disc also requires thin layers for narrow beam and shorter wavelength blue laser. The first BD-ROM player (Samsung BD-P1000) was shipped in mid-June 2006. The first Blu-ray Disc title was released by Sony and MGM on June 20, 2006. The first mass-market Blu-ray Disc hard disk drives for PCs are the BWU-100A , released by Sony on July 18, 2006.
Maps Optical disc drive
Main components
Laser and optics
The most important part of the optical disc drive is the optical path, placed in the pickup head (PUH), usually consisting of a semiconductor laser, a lens to focus the laser beam , and a diode to detect the reflected light from the disk surface.
Initially, a CD type laser with a wavelength of 780 n (in infrared) is used. For DVDs, the wavelength is reduced to 650Ã, nm (red), and for Blu-ray Disc it decreases further to 405Ã,m (purple).
Two main servomechanisms are used, the first to maintain the proper spacing between the lens and the disk, to ensure the laser beam is focused as a small laser point on the disk. The second servo moves the picking head along the radius of the disk, keeping the beam in the path of , the continuous spiral data path. Optical disc media 'reads' from the inside radius to the outer edge.
On read only media (ROM), during the creation process, the track is formed by pressing the thermoplastic resin into a 'master' glass with a raised 'bulge' on a flat surface, making holes << i> > and landed on a plastic disk. Because the depth of the hole is approximately one quarter to one-sixth of the laser wavelength, the reflected light phase shifts in relation to incoming light, causing a common destructive disorder and reducing the intensity of reflected rays. This is detected by a photodiode that creates an appropriate electrical signal.
An optical disc recorder encodes (also known as burning) data into recordable CD-R, DVD-R, DVD R, or BD-R disks (called empty ) by selectively heating the dye layer organic with laser. This changes the reflectivity of the dye, thus creating a readable sign like a hole and landing on a pressed disc. For recordable discs, the process is permanent and the media can be written only once. While laser reading is usually no stronger than 5 mW, laser writing is much stronger. The higher the writing speed, the less laser time to heat the point on the media, so the power should increase proportionately. DVD burners' lasers often peak at about 200 mW, both in continuous waves and pulses, although some have been driven up to 400 mW before diodes fail.
For CD-RW, DVD-RW, DVD RW, DVD-RAM or BD-RE rewritable media, lasers are used to melt crystal metal alloys in the disk recording layer. Depending on the amount of power used, the substance can be allowed to melt back (change the back phase) into crystalline or left behind in amorphous form, allowing for signs of the various reflectivities to be made.
Two sides media can be used, but they are not easily accessible with standard drives, as they must be physically submitted to access data on the other side.
Double layer (DL) media has two independent data layers separated by a semi-reflective layer. Both layers are accessible from the same side, but require optics to change laser focus. Traditional single layer writing media (SL) is produced with a spiral groove formed on a protective polycarbonate layer (not in the data recording layer), to lead and synchronize the head speed of the recording. The double-layered writing media has: first polycarbonate layer with groove (shallow), first data layer, semi-reflective layer, second polycarbonate (spacer) layer with another groove (inside), and second data layer. The first groove spiral usually begins on the inner edge and extends outward, while the second groove begins on the outer edge and extends inward.
Some drives support Hewlett-Packard LightScribe photothermal printing technology for special coated disk labels.
Rotation mechanism
Rotation mechanisms in optical drives are very different from those on the hard disk drive, where the latter keeps a constant angular velocity (CAV), in other words a constant amount per minute (RPM). With CAV, higher throughput can generally be achieved on an outer disk compared to the inside.
On the other hand, optical drives are developed with the assumption of achieving a constant throughput, on initial CD drives equal to 150 KiB/s. It is an important feature for streaming audio data which always tends to require constant bit rate. But to ensure no disk capacity is wasted, the head must transfer data at a maximum linear rate at any time as well, without slowing the outer rim of the disc. This causes the optical drive - up to now - to operate with a constant linear velocity (CLV). Spiral grooves of discs pass under his head at constant speed. The implication of CLV, as opposed to CAV, is that the discus angle velocity is no longer constant, and the spindle motor needs to be designed to vary its speed from between 200 RPM on the outer edge and 500 RPM on the inside.
Then CD drives continue the CLV paradigm, but evolve to achieve higher rotational speeds, popularly described in multiples of the basic speed. As a result, the 4ÃÆ' drive, for example, will rotate at 800-2000 RPM, while transferring data stable at 600 KiB/s, which equals 4 ÃÆ'â € "150 KiB/s.
For DVD, the base or 1ÃÆ'â € "speed is 1.385Ã, MB/s, equal to 1.32Ã, MiB/s, about nine times faster than the base speed of the CD. For Blu-ray drives, the base speed is 6.74Ã, MB/s, equal to 6.43Ã, MiB/s.
Because maintaining a constant transfer rate for all disks is of little importance in most contemporary CD uses, a pure CLV approach must be abandoned to keep disk speeds at a safe low while maximizing data rates. Some drives work in a partial CLV scheme (PCLV), by switching from CLV to CAV only when the rotation limit is reached. But switching to CAV requires major changes in hardware design, so most drives use a constant linear velocity scheme (Z-CLV). It splits the disk into multiple zones, each having a constant linear velocity. Z-CLV recorders rated "52ÃÆ'â €" ", for example, will write at 20Ã diâ €" in the deepest zone and then progressively increase the speed in a few separate steps up to 52ÃÆ'â € "on the outer edge. Without a higher rotational speed, improved read performance can be achieved by simultaneously reading more than one data flow point, but drives with the mechanism are more expensive, less compatible, and very unusual.
Restrict
Both DVD and CDs have been known to explode when damaged or spin with excessive speed. This imposes a constraint on maximum speed (56 Ã- for CD or about 18ÃÆ'â € "in DVD case) where the drive can operate.
Loading mechanism
The current optical drive uses a unloading mechanism, in which the disc is loaded into a motorized or manual operated tray, or a slot-loading mechanism, in which the disc is shifted into the slot and drawn by a motorized roller. With both types of mechanisms, if the CD or DVD is left in the drive after the computer shuts down, the disk can not be removed using the normal drive release mechanism. However, the tray loading drive takes account of this situation by providing a small opening where one can insert a straightened paper clip to manually open the drive tray to take the disc. Slot-loading optical disc drives have the disadvantage that they typically can not accept smaller 80 mm discs (except 80 mm optical disc adapter in use) or non-standard sizes, usually have no emergency ejects or eject buttons, and therefore should be disassembled if the optical disc can not be removed normally. However, Nintendo Wii, due to backwards compatibility with Nintendo GameCube games, and PlayStation 3 video game consoles can load standard-sized DVDs and 80 mm discs on the same slot-loading drive.
A small number of drive models, most compact portable units, have a top-loading mechanism where the drive cap is opened up and the disk is placed directly into the spindle (for example, all PlayStation One consoles, portable CD players, and multiple recorders Stand-alone CDs all feature a top-loading loader). It sometimes has the advantage of using spherical springs to hold the disk in place, minimizing damage to the disk if the drive is moved while it is rotating.
Some early CD-ROM drives use a mechanism in which the CD should be inserted into a special cartridge or caddies, somewhat similar in appearance to a 3.5 "floppy diskette. It is intended to protect the disk from accidental damage by covering it in a harder plastic casing , but does not receive wide acceptance due to additional cost and compatibility issues - the drive will also uncomfortably require a "blank" disc to be manually inserted into a caddy that can be opened before use Ultra Density Optical and Universal Media Disc use disk cartridges optics.
There are also some early CD-ROM drives for desktop PCs where the tray-loading mechanism will take out a bit and the user has to manually remove the tray to load the CD, similar to the tray discharge method used in the modern laptop's internal optical disk drive. and a sleek modern portable external optical disk drive. Like a top-loading mechanism, they have spring ball bearings on spindles.
Computer interface
Most of the internal drives for personal computers, servers, and workstations are designed to fit the standard 5.25 "hard drives and connect to their hosts via ATA or SATA interfaces.In addition, there may be digital and analog outputs for audio.The output can be connected via header cable to the sound card or motherboard. At that time, computer software that resembles a CD player controls the playback of a CD. At this time the information is extracted from the disk as data, to be played back or converted to other file formats.
External drives usually have a USB or FireWire interface. Some portable versions for laptops move themselves from batteries or directly from their interface bus.
Drives with SCSI interfaces are created, but they are less common and tend to be more expensive, due to the cost of their interface chipsets, more complex SCSI connectors, and smaller sales volumes.
When the optical disk drive was first developed, it was not easy to add to a computer system. Some computers like the IBM PS/2 have standardized on 3.5 "floppy and 3.5" diskettes, and do not include a place for large internal devices. Also IBM PCs and clones initially only include a single ATA (parallel) drive interface, which at the time the CDROM was introduced, was already used to support two hard drives. Early laptops simply do not have a high-speed built-in interface to support external storage devices.
This is solved through several techniques:
- The original sound card may include a CD-ROM drive interface. Initially, the interface belongs to each CD-ROM manufacturer. Sound cards can often have two or three different interfaces that can communicate with a cdrom drive.
- An external parallel port drive developed that is connected between the printer and the computer. It's a slow but option for laptops.
- The PCMCIA optical drive interface was also developed for laptops.
- SCSI cards can be installed on a desktop PC for an external SCSI drive enclosure, although SCSI is usually much more expensive than other options.
Internal drive mechanism
The optical drive in the photo is shown on the top right side; the disk will be above them. Laser and optical systems scan the bottom of the disc.
With reference to the top photo, just to the right of the image center is a disc motor, a metal cylinder, with a gray-centered hub and a black rubber drive ring at the top. There are round disc-shaped clasps, which are loosely held inside the cover and freely rotate; it's not in the photo. After the disk tray stops moving inside, when the motor and its mounted parts are rising, a magnet near the top of the rotating assembly contacts and attracts a clamp to hold and center the disc. This motor is a "brushless" brushless DC motor that has an external rotor - every part that looks spinning.
Two parallel guide rails running between the top and bottom left in the photo carry "sled," the optical read-write head moves. As shown, this "sled" is close, or at a position where it reads or writes on the edge of the disc. To move the "glide" during continuous read or write operation, the stepper motor rotates the leadscrew to move the "sled" across its total travel range. The motor itself, is a short gray cylinder just to the left of the most distant surprise mountain; its axis parallel to the supporting rod. Leadscrew is a stem with darker detail and more evenly; this is a helical groove that binds pins to a "sled".
Instead, the mechanism shown in the second photo, which comes from a cheap DVD player, uses a less accurate and less efficient DC motor to drive the sled and rotate the disc. Some older drives use a DC motor to move the sled, but also have a magnetic rotary encoder to track position. Most drives on a computer use a stepper motor.
The gray metal chassis is mounted in four corners to reduce the sensitivity to external shocks, and to reduce the driving noise from residual imbalances while sprinting. Grommet soft shock mounts are located just below the colored screw on all four corners (the left is obfuscated).
In the third photo, the components under the lens cover mechanism are visible. Two permanent magnets on both sides of the lens holders and the coils that move the lens can be seen. This allows the lens to be moved up, down, forward, and backward to stabilize the focus of the light.
In the fourth photo, the inside of the optical package is visible. Note that since this is a CD-ROM drive, there is only one laser, which is a black component that is attached to the lower left part of the assembly. Right above the laser is the first focusing lens and prism that directs the rays on the disc. The tall, thin object in the center is a half silver mirror that divides the laser beam in different directions. To the bottom right of the mirror is the main photodiode that senses the reflected light from the disc. Above the main photodiode is the second photodiode used to sense and regulate the power of the laser.
The irregular orange material is a flexible engraved copper foil supported by a thin plastic sheet; this is a "flexible print circuit" that connects everything to electronics (not shown).
Compatibility
Most optical drives are compatible with their ancestors to CDs, although this is not required by the standard.
Compared to the 1.2 mm CD layer of polycarbonate, the DVD laser beam only has to penetrate 0.6 mm to reach the recording surface. This allows the DVD drive to focus the rays on a smaller spot size and to read smaller holes. The DVD lens supports different focus for CD or DVD media with the same laser. With newer Blu-ray disk drives, lasers only have to penetrate 0.1 mm material. Thus optical assembly should normally have a larger focus range. In practice, the Blu-ray optical system is separate from the DVD/CD system.
Recording performance
During the CD writer drive period, they are often marked with three different speed ratings. In this case, the first speed is to write-once (R) operation, second speed for rewriting (RW) operation, and last velocity for read-only operation (ROM). For example, the CD writer drive 40ÃÆ'â € "/16ÃÆ'â €"/48ÃÆ'â € "was able to write to CD-R media at speeds of 40ÃÆ'â €" (6,000 KB/s), write to CD-RW media at speeds of 16ÃÆ'â € "(2,400 KB )./s), and read from CD-ROM media with speed of 48ÃÆ'â € "(7.200 KB/sec).
During the combo drive time (CD-RW/DVD-ROM), the additional speed rating (eg 16ÃÆ'â € "in 52ÃÆ'â €/32ÃÆ'â €"/52ÃÆ'â € "/16ÃÆ'â €") is intended for DVD-ROM readout operations.
For DVD writer drives, Blu-ray disc combo drives, and Blu-ray disc writer drives, the speed of writing and reading of each optical medium is specified in the retail box, user manual, or bundle of brochures or pamphlets.
In the late 1990s, buffer underruns became a very common problem because high-speed CD recorders began appearing on home and office computers, which - for various reasons - often could not collect performance to keep the data flow to the recorder continues to eat. The recorder, if short run, will be forced to stop the recording process, leaving a truncated trail that usually makes the disc useless.
In response, CD recorder manufacturers began to send drives with "underrun buffer protection" (under various trade names, such as Sanyo's "BURN-Proof", "JustLink" Ricoh and "Lossless Link" Yamaha). This can delay and continue the recording process in such a way that generating discharge gaps can be handled by error correction logic built into CD players and CD-ROM drives. The first of these drives is rated at 12ÃÆ'â € "and 16ÃÆ'â €".
While drives burn DVD R, DVD RW and all Blu-ray formats, they do not require errors such as correcting the correction because the recorder can put new data right at the end of a suspended writing effectively generates a continuous track. (this is what DVD technology has achieved). Although the interface is then capable of streaming data at the required speed, many drives are now writing in a 'constant linear velocity zonation'. This means that the drive should temporarily suspend the write operation while it changes the speed and then resumes once the new speed is reached. This is handled in the same way as the underrun buffer.
The optical disk drive's internal drive buffer is: 8 MiB or 4 MiB when recording BD-R/BD-R DL/BD-RE/BD-RE DL media; 2 MiB when recording DVD-R/DVD-RW/DVD-R DL/DVD R/DVD RW/DVD RW DL/DVD-RAM/CD-R/CD-RW media.
Recording scheme
CD recording on a personal computer is initially a batch-oriented task because it requires special author software to create "images" of data to record, and record it to disk in one session. This is acceptable for archival purposes, but limits the general convenience of CD-R and CD-RW as removable storage media.
Package writing is a scheme in which recorders write gradually to disk in short bursts, or packets. Writing sequential packets fills the disk with packages from the bottom up. To make it readable in CD-ROM and DVD-ROM drives, the disk can be closed at any time by writing the final contents list at the beginning of the disk; after that, the disk can not be written-packet any further. Writing packages, along with support from operating systems and file systems such as UDF, can be used to mimic random write access such as in media such as flash memory and magnetic disks.
Writing fixed-length packets (on CD-RW and DVD-RW media) splits disks into fixed-sized packets. Padding reduces disk capacity, but allows the recorder to start and stop recording on individual packets without affecting its neighbors. It resembles the write-write access offered by the magnetic medium close enough that many conventional file systems will work as they are. Such disks, however, can not be read on most CD-ROM and DVD-ROM drives or on most operating systems without additional third-party drivers. Distribution into packages is unreliable as it might seem like CD-R (W) and DVD-R (W) drives can only place data into data blocks. Although the cheap distance (the above-mentioned padding) is left in between the blocks, the drive can sometimes lose and destroy some of the existing data or even make the disk unreadable.
The DVD RW disk format eliminates this unreliable by incrementing more accurate timing instructions in the disk data flows and allowing individual data blocks (or even bytes) to be replaced without affecting backward compatibility (a feature dubbed "non-loss linking"). The format itself is designed to handle disconnected recording because it is expected to be widely used in digital video recorders. Many such DVRs use video compression schemes at variable rates that require them to record in short bursts; some allow simultaneous playback and recording by alternating rapidly between recording to disk tails while reading from elsewhere. Blu-ray disc system also includes this technology.
Mount Rainier aims to make CD-RW and DVD RW discs conveniently written comfortably used as removable magnetic media by installing firmware firmware discs in the background and managing media defects (by mapping out parts of discs that have been obsoleted with delete cycles to spare space elsewhere on disk). In February 2007, support for Mount Rainier was natively supported in Windows Vista. All previous versions of Windows require third-party solutions, such as Mac OS X.
Unique Recorders
Due to pressure from the music industry, as represented by IFPI and RIAA, Philips developed the Recorder Identification Code (RID) to allow the media uniquely associated with the recorder that has written it. This standard is listed in Rainbow Books. The RID-Code consists of supplier code (eg "PHI" for Philips), model number and unique recorder ID. Quoting Philips, RID "allows the trace for each disk back to the exact machine where it was created using the information encoded in the tape itself.Using the RID code is mandatory."
Although RID is introduced for the music and video industry, RID is included on every disk written by every drive, including data and backup disks. The value of RID is questionable because it is currently (unlikely) to find individual recorders because there is no database.
Source Identification Code
Source IDentification Code (SID) is an eight-character supplier code placed on the optical disc by the manufacturer. SID identifies not only the manufacturer, but also individual factories and machines that generate disks.
According to Phillips, the administrator of the SID code, the SID code provides an optical disk production facility with the means to identify all discs that are mastered or replicated in the factory, including special Laser Beam Recorder (LBR) signal processors or prints that produce capers or disks.
Use of shared RID and SID in forensics
The use of RID and SID standards means that each disk that is written contains a record of the machine that generated the disk (SID), and which drive wrote it (RID). This combined knowledge may be very useful for law enforcement, to investigative agencies, and to private or corporate investigators.
See also
References
External links
- How CD Works in HowStuffWorks
- How CD Burning Works in HowStuffWorks
- Understanding CD-R & amp; CD-RW
- CD-Recordable FAQ
- News/reviews CD/DVD/Blu-ray
- Why Audio CD-R Disc Will Not Always Play
- How to Fix Correct CD Burner Driver
- IDE ODD (Top) and SATA ODD (Bottom). Both are designed for laptops.
- An ODD IDE. It is a 5.25 inch form factor.
- A SATA ODD. It is a 5.25 inch form factor.
Source of the article : Wikipedia
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