It's so named because it stores nearly five gigabytes GB of information. The laser that "reads" the information first interprets the data on the top disc and then changes angle to translate the data on the second one. The DVD works in the same way, except that both the discs are double-sided. Instead of just reading one side for information, the laser reads both sides, something like our old vinyl records.
If you're in the movie rental business that means more long-term profits as you won't have to pay for replacement versions after multiple plays. It has the added advantage that the local franchise won't have to worry about whether you rewind it or not.
In addition, because of special features within the television set DVD player units, it will be impossible for these sets to "read" and play pirated copies of movies on DVD, a problem that has plagued Hollywood's video market abroad.
This micrograph shows a commercial die, into which CD manufacturers inject molten polycarbonate plastic to form the pits and lands of an individual disc. DVD digital video disc is a technology based on optical data storage similar to compact disc CD. Optical data storage is a method of storing digital information 1's and 0's by using light to read the information. Analog information is converted into digital information, which is then encoded onto the disc from the inside edge out.
Digital data are encoded by means of pits on the recording layer of the disc. The pits and the separations between pits, called lands, vary in length to represent the digital information stored in the disc. The pits are arranged in a track that forms a spiral pattern on the recording layer of the disc. The disc revolves in a circular motion inside the player, while an optical head laser slowly moves outward and remains focused on the pits.
The laser beam is reflected back to a detector when it hits the lands, and it is scattered away from the detector by the pits. The transition between a pit and a land corresponds to a "1" in the digital bit stream. A DVD can store over two hours of video on one layer of the disc. In comparison to the 74 minutes of data that a CD can hold, this capacity marks a vast improvement.
The smallest pits on a DVD are about 0. The pits are arranged in tracks called track pitch that are spaced much closer on a DVD 0. With this construction, a single layer, single-sided DVD can hold 4.
Pits burned into a recordable CD-ROM, shown in the scanning electron micrograph above, are rougher around the edges than pits in a commercially stamped CD. Updated: May 12, They have been used for recording audio tracks up to 80 minutes. Are CD-Rs still used? CD-R discs are still used for audio recording, though CDs sales have plummeted in recent years, so less of them are being produced and used.
Do blank CD-Rs go bad? If kept in a fine casing, a good quality blank CD-R has an estimated shelf-life of around five to 10 years, according to an estimation by the Optical Storage Technology Association. The difference is in the number of times data can be recorded. A CD-R can only have data written once while a CD-RW is rewritable, allowing you to erase and rewrite the data as many times as you want. What is the best brand of blank CD-R? Thank you for making all of these interesting articles, do you have one on cassette tapes?
Feb 25, Steven Feb 22, Feb 24, Lucas Feb 19, I learned what cd means it means compact discs. Feb 21, That's right, Lucas! Adriel Feb 18, Feb 19, Is there similar things that work like the cds. Feb 13, Mariah butler Feb 10, I never knew a laser beam helps a cd play that is amazing but how do video games work.
Feb 11, Anthony Feb 7, How do video games work? Is it the same thing? Feb 8, Feb 4, Thank you for sharing your thoughts, sophia! Connor Feb 3, Feb 3, Feb 2, LaBelle Jan 29, Today was my class's first visit to Wonderopolis!
Thank you for teaching us how CDs are made. Gabe Feb 1, Wow this was really cool and helpful. Hi, Gabe! We're glad this Wonder was helpful! Jan 29, Aileen Jan 29, Why doesn't California have tornadoes or hurricanes? Ethangamertv Jan 29, Jan 31, We're glad it was helpful! Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it.
The label is then printed onto the acrylic. A cross section of a complete CD not to scale looks like this:. A CD has a single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the center means that the CD can be smaller than 4.
CD business cards hold about 2 MB of data before the size and shape of the card cuts off the spiral. What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0. A micron is a millionth of a meter.
And the bumps are even more miniscule The elongated bumps that make up the track are each 0. A nanometer is a billionth of a meter. Looking through the polycarbonate layer at the bumps, they look something like this:. You will often read about "pits" on a CD instead of bumps. They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps.
The incredibly small dimensions of the bumps make the spiral track on a CD extremely long. If you could lift the data track off a CD and stretch it out into a straight line, it would be 0. To read something this small you need an incredibly precise disc-reading mechanism. Let's take a look at that. The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:.
Inside the CD player, there is a good bit of computer technology involved in forming the data into understandable data blocks and sending them either to the DAC in the case of an audio CD or to the computer in the case of a CD-ROM drive. The fundamental job of the CD player is to focus the laser on the track of bumps.
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