DVD Player

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.

History

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.

Design

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.

Raw Materials

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.

Disk materials

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.

Final assembly

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.

Quality Control

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.

The Future

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.

digital:

Pertaining to information that has been translated into a number code.

laser:

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.

microchip:

A small piece of semiconductor material, such as silicon, that carries electronically connected parts.

optical:

Pertaining to or using light.

photodiode:

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.

semiconductor:

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

Books

Morgan, Nina. Lasers. Austin, TX: Steck-Vaughn Company, 1997.

Ross, John. DVD Player Fundamentals. Indianapolis, IN: Sams Technical Publishing, 2000.

Periodicals

"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.