A DVD is the same size and thickness as a CD, but it can hold at least seven times more data.
A digital video disk or digital versatile disk (DVD) is an optical (using light) storage medium with digital data, or information that has been translated into a number code. A laser (a narrow, intense beam of light) is used to store the digital information on a DVD in the form of indentations called pits (holes) and lands (surfaces between the pits).
The indentations are laid out on a continuous spiral track, which starts near the center of the disk, circling around the whole disk in a structure similar to that found on vinyl records. Laser is again used in recovering the stored information on the DVD. Using a laser beam, the DVD player "reads" the indentations, reproducing the movie, music, or data stored in the disk.
The idea of storing information in a device and then reproducing that information goes back to the early nineteenth century. In 1801, French silk weaver Joseph-Marie Jacquard (1752–1834) invented a series of punched metal cards to store information for weaving patterns. Jacquard's loom, controlled by the information stored in the punch cards, made complicated patterns automatically. In fact, the idea behind Jacquard's invention was initially responsible for the idea of storing programs for computers.
The development of DVD players began with the introduction of the first audio (sound) CDs (compact disks) and CD players in the early 1980s. Video (visual) CD players were introduced later in the decade, although they never became popular enough to replace videocassette recorders (VCRs).
As other advancements in CD technology were occurring, including computer CDs and recordable CD players, researchers continued to search for ways to improve the storage capacity of CDs. Then, scientists discovered that they could use a red laser to place more pits on the surface of the disk. (Laser light, unlike ordinary light that spreads out in all directions, is tightly focused and intense.) This led to the creation of the DVD. In 1997, the first DVD players were introduced.
Packing it in
The DVD was developed as an improved form of CD technology. The same size (4.75 inches, or 12 centimeters, in diameter) and thickness (1.2 millimeters) as the CD, the DVD can hold at least seven times more data. A DVD can store much more information than a CD because the pits are smaller than those on a CD; therefore, more pits can fit on a track. Also, the tracks are arranged closer together, allowing for more tracks on the disk. Scientists observe that if the whole spiral track could be taken off a single-sided, single-layer DVD disk and placed in a straight line, it would measure over seven miles long.
DVDs vary in the amount of storage space, depending upon their physical structures. In terms of movies, the amount of viewing time can range from about two hours for a single-sided, single-layer disk to eight hours for a double-sided, double-layer disk. In comparison, a CD stores about seventy-five minutes of music. No matter how many layers are in the DVD disk, the thickness remains the same.
Although the disk is capable of storing a large amount of data, it cannot hold all the information of a full-length movie. In order to fit the movie on a disk, the moviemaker uses a compression method to reduce the amount of data stored. Each second of a movie consists of about thirty still (nonmoving) images called frames. When played in fast motion, the frames are translated by the human brain and seen by the human eye as one movement. Therefore, a movie calls for a huge number of still frames. During the process of compression, a frame that is similar to a previous frame is removed, thus allowing more room for storage.
A versatile machine
The DVD player is quite versatile (having varied functions). It is backwards-compatible, which means that the machine can play CD music. In contrast, a CD player cannot play DVD music. DVD players that hold more than one disk are called changers. A jukebox-type player can store up to two hundred disks to house an entire music or movie collection.
The player is so powerful it can read the second layer of stored data of a single-sided disk through the first layer, so that there is no need to flip the disk over. Starting at the center of the disk, the laser reads the first layer of pits and lands, continuously moving outward. When the laser reaches the end of the spiral track at the outermost part of the disk, the player quickly refocuses the laser beam on the second layer. Without missing a beat, the player reads the disk, staying at the outer part of the disk, but proceeding in the opposite direction. There is no interruption in the movie sequence because the data on the second layer has been recorded backwards.
The player also has the ability to decompress the data stored on a DVD. It rebuilds the whole movie as the viewer is watching it, filling in the missing information that had been eliminated during the compression process (see above).
DVD players that reproduce movies
DVD data can come in the form of video, audio, or computer information. The following explanation will focus on DVD players that hook up to a television set for watching movies. A typical single-sided, single-layer DVD disk contains about two hours of movie.
DVD players reproduce home movies that are comparable to cinema movies in picture quality and sound. Since no part of the DVD player touches the disk when the movie is playing, the picture and sound quality of the movie remains the same as the first time it was played. Compare this to a video tape that loses some of its original picture and sound quality every time it is played.
A DVD player lets the viewer access standard DVD features, including different languages (up to eight languages), various subtitles (up to thirty-two languages), behind-the-scenes footage, and a wide-screen image, even when viewed on a standard television screen. Other features include uncut versions of the film, closed-captioned viewing (text of the audio information) for the hearing-impaired, and parental locks, by which an adult could set the machine to play the PG-rated version of an R-rated movie. The DVD video may also include commentary tracks, in which an individual connected to the movie talks about it as the film unfolds. Then, there are hidden surprises, such as previews of other movies.
DVD players are designed like CD players. The simple exterior is made of plastic, with a front panel of plastic buttons. Some players have a plastic tray that comes out of the machine to accept disks. Others have an automatic feed system into which the disk is inserted.
Like a CD player, a DVD player has three main components—a disk drive mechanism, an optical assembly system, and an internal electronic circuit board. The disk drive mechanism typically consists of a spindle that holds the disk and a motor that spins it. The optical system assembly includes the laser, the photodiode (also called a photosensor), lenses, and mirrors. The circuit board contains all the electronic pieces for converting the data into the original movie recorded on the DVD disk.
How does it work?
When a disk is inserted into a DVD player, the player spins it and focuses a laser beam on the spiral track containing the pits and lands. The lens and prism (mirror) help focus the laser beam properly. As the laser hits the pits and lands, light of varying intensity is reflected back by the disk. The photodiode, which is light-sensitive, reads the variations in light intensity and converts them into electrical signals. The signals are passed on to the electronic circuit board, which in turn recreates the movie.
A portable movie theater
DVD players can come as portable units that look like laptop computers. They not only play movies, but also CDs. They are lightweight and have a rechargeable battery pack. The screen is typically about seven inches, although the smallest player has a 5.8-inch screen. As with regular-sized machines, portable units play movies and music of excellent quality.
The DVD player and disk are made out of a variety of materials. Some are familiar materials such as glass and plastic, while others are less known.
DVD player materials
The cabinet that houses the different components of the DVD player is made of aluminum. The laser device consists of a glass tube filled with gas, as well as a small power supply to produce the laser beam. The photodiode and the main components on the circuit board are typically made of silicon. Silicon is a nonmetallic material that can conduct electricity. Its unique ability to act as an off–on switch makes it a valuable component of electronic equipment.
Polycarbonate plastic, the same material used in making bulletproof windows, makes up the base material of the disk. The plastic is coated with a thin layer of metal, such as aluminum, silver, or gold, for reflecting the laser light. It is on the metal that the pits and lands are recorded. The surface of the disk is further coated with a hard layer of lacquer to protect it from damage. Finally, a label is applied over the disk.
The Manufacturing Process
The components of a DVD player are made by separate companies and then put together by the manufacturer. The main components include the optical system assembly, disk drive mechanism, and internal electronic circuit board.
SLEEK AND SLIM
A new addition to the family of DVD players is a space-saver measuring 10 inches (252 mm) by 7.25 inches (184 mm) by 2.4 inches (61 mm). Unlike the traditional desktop players, Sony's DVD Style Cube can be positioned and operated in three ways—vertically, horizontally, or mounted to the wall. It comes in silver or black, has a slot-loading disk mechanism, and is intended for use in any room in the house.
Optical system assembly
1 The optical assembly system is made up of a laser, photodiode, prism, and lenses. The laser and photodiode are placed on a plastic housing, and the other components are placed in specific places. Each piece has to be arranged just right, or the system will not perform properly. Electrical connections are put in place, and the optical system is ready to be attached to the disk drive mechanism.
Disk drive mechanism
2 The optical system assembly is connected to the motor that will drive it. The motor is then connected to the other parts of the disk drive, including the loading tray (if present) and the spindle motor. After other gear and belts are attached, the entire assembly is placed in the main body.
Internal electronic circuit board
3 The process of putting the circuit board together is done in a clean room kept free of nearly all dust particles that can damage the board. A printed board showing how the different electronic components should be arranged is passed through a series of machines. Electronic pieces, including microchips that direct the electronic processes of the machine, are plugged into the board. Then the board with the electronic pieces on it is washed to further clean it in preparation for soldering.
4 Soldering is the process by which the electronic pieces are permanently attached to the board. This is done by passing the bottom of the board through solder (a mixture of metals) that has been melted, filling the appropriate spots that would hold the components in place. As the board is allowed to cool, the solder hardens, holding the pieces in place.
5 When all the components are ready, the electronic board is hooked to the rest of the machine, and the main cover is attached. The finished DVD players are sent to a packaging station where they are boxed along with accessories, such as disks, manuals, and power cords.
To ensure the quality of the DVD players, visual and electrical inspections are done throughout the entire production process. Defects that are found are corrected. In addition, each machine is played to see if it performs as expected. The testing is done under different conditions, such as excessive heat and humidity.
Even though DVD technology is relatively new, DVD players are expected to replace both VCRs and CD players in the early twentieth century. Researchers continue to look for ways to fit more data on the DVD disk. An area of research includes new laser technologies involving more powerful lasers to both write and read the data that make up a movie. Blue laser, narrower and brighter than the red laser, could help store more data on a disk. In the meantime, almost every recent movie has been made available on DVD. In addition, old movies are being converted to DVD form.
ONE FOR THE ROAD
Children on long car rides have no more reason to ask, "Are we there yet?" The in-dash DVD players have transformed cars into mobile movie theaters, with the same features as home video entertainment. CD capability gives car occupants the option of simply listening to music.
Manufacturers continue to improve on the standard DVD player. For those consumers who want the option of a VCR, some manufacturers have combined a DVD player with a VCR to form one unit. A person can watch a DVD movie and tape a television program onto the VCR tape at the same time. Experts foresee the combination of DVD and Internet technologies, in which the high-quality video and audio content of a DVD would be combined with the ever-changing information from the Internet.
- compact disk (CD):
- Like the DVD, the CD is an optical storage medium with digital information. CDs typically store recorded music.
- Pertaining to information that has been translated into a number code.
- Stands for Light Amplification by Simulated Emission of Radiation. It can refer to the device that produces the light beam or the light beam itself. Unlike ordinary light, which consists of different colors and spreads out in many directions, laser is a single intense color that stays focused in one direction.
- A small piece of semiconductor material, such as silicon, that carries electronically connected parts.
- Pertaining to or using light.
- Also called a photosensor; a light-sensitive device that changes a light code into electrical signals.
- pits and lands:
- Microscopic indentations on a DVD that store the information used to recreate a movie.
- A nonmetallic material that conducts electricity.
- videocassette recorder (VCR):
- A device that records and plays back television programs and movies by means of a videotape contained in a rectangular plastic case.
For More Information
Morgan, Nina. Lasers. Austin, TX: Steck-Vaughn Company, 1997.
Ross, John. DVD Player Fundamentals. Indianapolis, IN: Sams Technical Publishing, 2000.
"The Disc That Saved Hollywood: Jealous execs... Backroom deals... The inside story of how DVDs became the entertainment industry's most lucrative product." Newsweek. (August 20, 2001): pp. 30-33.
"DVD Players." Consumer Reports. (December 2001): pp. 30-33.
Poor, Alfred. "CDs and DVDs." PC Magazine. (May 4, 1999): pp. 207-209.
Digital video disk or digital versatile disk (DVD) is a type of optical data storage medium capable of holding up to 17 giga-bytes (GB) of information. First introduced during the mid-1990s, they were developed as an improved form of compact disk (CD) technology. DVDs can produce such high quality pictures and sounds, they are expected to eventually replace both VCRs and CD players. It is anticipated that the market for DVD players will reach 10 million units by the year 2000.
DVDs work much the same way as conventional CDs. Just like in a CD, the information is coded as a series of tiny pits in the disk. The pits are organized on a spiral track in a structure similar to vinyl records. By using a laser, these pits can be interpreted as binary code. When a smooth surface is read, the machine interprets the data point as a 0. When a pit is encountered, the data point is read as a 1. However, the key innovation that makes DVDs superior to CDs is the laser used to read and create the pits. DVDs use a shorter-wavelength, red laser that can place pits more densely on the surfaces of the disks. This not only allows for more data, it also requires that the disks be only half as thick as conventional CDs. Consequently, two layers can be bonded together to create a double-sided disk which has the same thickness as a CD (1.2 mm).
The DVD system has three features, which make it highly desirable including its high storage capacity, interoperability, and back-ward compatibility. In the early stages of DVD introductions, a single disk will hold as much as 4.7 GB of information. This is roughly equivalent to seven CD-ROMs. In future releases of this technology, a disk may hold up to 17 GB. This amount of storage space will literally change the way computer programs are developed and will allow for the inclusion of more video clips. The data format and laser used in DVDs will be the same for the computer players as for the television players. This will enable consumers to play the same disks in their computers that they play on their TV. DVD players will also have the ability to play current technology CDs. In this way, consumers will not have to buy replacement products for their current CD collections.
DVDs can be used for a variety of applications including movies, audio systems, computers, and video games. Since the in-formation stored on these disks are electronic, the picture quality is estimated to be three times better than conventional VHS pictures. Additionally, the picture will not degenerate with age or use. Computer programs will also benefit from DVDs. For example, programs, which used to take up multiple CDs can now be condensed onto a single DVD. Video games will also benefit from DVD technology. Since DVDs offer high memory and interactivity possibilities, video clips can be included to enhance the playing experience.
Developing the ability to store data for later retrieval has always been important. The first true data storage and retrieval systems were journals and ledgers. While they are still used today, they are slow, inefficient, and bulky. When the computer was being developed during the 1950s and 1960s, one of their main benefits was their ability to store and retrieve data quickly. This has now become one of the cornerstones of information storage and retrieval. Early computerized storage mediums included such things as punch cards, vinyl LPs, magnetic tape, cartridges, and magnetic disks. As computers improved, so did the data storage capabilities. In the late 1970s, the internal hard drive was introduced. Each of these data storage systems were developed to improve on the convenience and efficiency of the best storage methods available. Many of these systems continue to be improved on even today.
The development of DVD began with the introduction by Sony of the CD in the early 1980s. This new storage medium employed a laser to read tiny pits carved in a disk. The first CD audio players were introduced in 1983. They were useful because it was possible to store more than 75 minutes of music on one disk. That was nearly twice what a vinyl LP could hold. While their acceptance was slow, the CD eventually replaced vinyl records as the preferred medium of choice for audio releases.
Video CD players were introduced later in the decade. For various reasons, they never became popular enough to replace VCRs. The use of CDs in computers began during 1987. These devices were useful because they allowed storage of up to 650 megabytes (MB) on a single disk. Until then, the maximum storage on a magnetic disk was 1.3MB. Early computer CDs were slower than typical disk drives and were read only. Data transfer speeds steadily increased as did their capacity to write data. In 1994, 4X speed CD-ROMs (Read Only Memory) were introduced. In the next two years this was doubled. By 1996, 24X speed CD ROMs were available. Recordable CD players were first produced in 1996.
Introduced in 1996, the multiple write CD was developed by Matsushita using a phase-change dual process. This uses a laser to change the reflective properties of the disk. Current CD-RW recorders can use this technology.
As all these advancements in CD technology were occurring, researchers continued to search for ways to improve the storage capacity of these machines. Then, scientists discovered that by using a shorter wavelength laser, much more data could be packed on a single disk. This led to the creation of the DVD. In 1997, the first DVD players were introduced. These machines are slower than the fastest CD players and are not yet recordable. However, the next generation DVDs that are scheduled for release during 1999 will be faster and employ recording technology. Eventually, DVD is expected to replace VCRs and CD players.
A DVD player is designed much like a CD player. For example, computer DVD drives are made the same size and shape as CD-ROM drives. They also have an outer plastic housing and come complete with plastic buttons on the front panel. Some DVD drives have a plastic tray, which extends out from the machine to accept disks. Others have an automatic feed system in which the disk is inserted. Inside the DVD drive, the electronics are also much the same as a CD-ROM drive. Both have sophisticated electronics and include a disk drive mechanism, a printed circuit board, and an optical system assembly. While DVD drive mechanisms come in various designs, each basically consists of a spindle that holds the disk and a motor that spins it. The circuit board contains all of the electronic components, which help convert the data being read into a usable format.
The optical system assembly is the part of the DVD that reads the data from the disk and transmits it to be converted into binary code. In a DVD machine, this consists of a redlaser diode, which has the ability to produce short-wavelength pulses. This is a low noise red laser producing light in the 600-650 nanometer (nm) range. It is much shorter than the 780 nm lasers used in conventional CDs. The other primary component of the optical system assembly is the photodiode, which receives the optical signal from the laser and converts it to an electronic signal. Highly polished lenses and mirrors make up the rest of the optical system assembly.
DVD disks also look like CD-ROMs, but the data is packed together more tightly. The surface of the disk is coated with a reflective silver layer that is protected by a thin, hard coating of lacquer. If a semitransparent gold layer is put on top of the reflective silver layer, the disk can be made to store 2 layers of data on one side. By using less power, the laser can read the data from the gold layer first and then by increasing the power, it can read the silver layer. This nearly doubles the capacity of one side to 8.5 GB. Eventually, a single double-sided disk will be able to hold up to 17 GB of data.
Since DVDs were invented primarily for movies, a compression system is required. To do this, manufacturers have agreed to use the MPEG-2 (Motion Picture Experts Group) compression system. This is a system in which only the elements of the picture that change from frame to frame are stored. For audio, Dolby digital compression is used. Because both of these compression systems are used, a decompressor or decoder must also be included in the DVD player. Currently, this is a separate card that plugs into the computer. The decoder board processes data from the disk and sends it right to the computer's graphics and audio system.
A variety of raw materials are used in the construction of DVD players and disks. Glass is used to make the laser and other diodes in the system. The primary components on the circuit board are made from silicon. Aluminum metal is used for the housing as well as a hard plastic. The base material of the disks is plastic. They are additionally coated with a silver colored layer and a thin gold layer. The surface of the disk is further coated with a hard layer of lacquer to protect it from damage.
The components of a DVD machine are typically manufactured by separate companies and then assembled by the DVD manufacturer. The production of the component parts is a highly specialized process, and only a few companies are equipped to supply the entire industry. The main components include the optical system assembly, internal electronic circuit board and the disk drive mechanism.
- 1 The optical system is made up of a laser, photodetector, prism, mirrors, and lenses. The laser and photodetector are installed on a plastic housing, and the other components are placed in specific places. Great care is taken in the positioning of each of these pieces because without proper alignment, the system will not perform properly. Electrical connections are attached and the optical system is then ready to be attached to the disk drive mechanism.
Disk drive mechanism
- 2 The optical system is attached to the motor that will drive it. This in turn is connected to the other principle parts of the disk drive including the loading tray (if present) and the spindle motor. Other gears and belts are attached and the entire assembly is placed in the main body.
- 3 The electronic components of the DVD machine are sophisticated and use the latest in electronic processing technology. The circuit board is produced much like that of other electronic equipment. The process begins with a board which has the electronic configuration printed on it. This board is then passed through a series of machines, which place the appropriate chips, diodes, capacitors and other electronic pieces in the appropriate places. The process is done in a clean room to prevent damage that can be caused by airborne dust. When completed, it is sent to the next step for soldering.
- 4 A wave-soldering machine is used to affix the electronic components to the board. Before a board is put into the machine however, it is first washed to remove any contaminants. The board is then heated using infrared heat. The underside of the board is passed over a wave of molten solder and through capillary action, the appropriate spots are filled. As the board is allowed to cool, the solder hardens holding the pieces in place.
Final assembly and packaging
- 5 When all the components are ready they are assembled to produce the final product. The electronic board is hooked up to the rest of the machine and the main cover is attached. The DVD machine is then sent along to a packaging station where they are boxed along with accessories such disks, manuals, and power cords. They are then put on pallets and sent to distributors and finally customers.
To ensure the quality of the DVD machines, visual and electrical inspections are done throughout the entire production process and most flaws are detected. Additionally, the functional performance of each completed DVD machine is tested to make sure it works. These tests are done under different environmental conditions such as excessive heat and humidity. They involve playing a test disk, which will produce specific electronic signals. Since most DVD manufacturers do not produce all of their own parts, they rely heavily on their suppliers for good quality. Most manufacturers set their own quality specifications, which their suppliers must meet.
DVD technology is relatively new. There are many areas which will be improved in the coming years. Key developments for DVD include greater storage capacity, improved reader capability, and an increase in the number of movies available in DVD format.
Currently, the most intensely studied area of DVD technology is increasing data storage capabilities. While the technology has already been developed to produce 17GB disks, some companies have found ways to store even more. A new encoding technique is being developed that can create a three-fold improvement in DVD storage. In this method, the pits made on the disk will have varying degrees of depth. This will allow the pit to encode for numbers from 0 to 8 instead of just a 0 or 1. It is anticipated that DVD devices using this technology will be available during 1999. Other storage mediums also show some promise. A new technology has recently been demonstrated that can hold up to 30 GB of data. This system uses red lasers and a magnetic field to retrieve the data. The use of blue lasers may allow for even greater storage capacity.
Another area of improvement will be found in the ability of the DVD players to read two layers of information on a single side of the disk. Even though DVD players can theoretically read two layers of information both layers are rarely used because of its high cost. As technology improves however, this obstacle should be overcome and the full potential of DVDs may be realized.
Currently, one the most inhibiting factors in the development of DVDs is the lack of a universal standard for storing and picking up media. This is similar to the problem that developed in the 1980s between VHS and Beta videotape players. In the near future, this problem should be resolved when major DVD manufacturers agree on a format.
Where to Learn More
Williams, G. Compact Disk Players. TAB Books, 1992.
Hogan, Dan. "I want my DVD." Current Science (October 3, 1997).
Vandendorpe, L. "A Rose by Any Other Name Couldn't Hold This Much Data." R&D Magazine (July 1997).
Poor, Alfred. "21st Century Storage." PC Magazine (January 21, 1997): 164.
Technology has brought personalized entertainment within the grasp of many consumers. For example, personal video recorders, like TiVo, store television programs for people to watch when they want. The system can also be programmed to know a user's favorite types of shows and record similar programs that might be of interest to the user.