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Video:DVD vs. CD: How Are They Different?

with Zoya Popova

DVDs and CDs are both optical discs, but there are important differences that give them separate purposes. Learn more about how DVDs and CDs work.See Transcript

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Transcript:DVD vs. CD: How Are They Different?

Hi, I'm Zoya Popova for About.com, and today we're going to talk about the differences between CD and DVD.

Similarities of CDs and DVDs

On the face of it, CDs and DVDs look very much alike. Both have a standard 12 cm diameter, and both are about 1.2 mm thick. What's even more important is that they are both optical discs, which means that the data stored on them is read by a laser. The laser goes over the pits and lands embedded onto the disc surface, and communicates a signal to the reading device that turns it into a digital code of 1s and 0s.

Structural Difference of DVDs and CDs

There are, however, significant differences. Let's take a look at their structure. The CD is composed of one thick layer of polycarbonate with a data layer on top, followed by a metal layer that reflects the laser beam onto the sensor, followed by a metal-protecting lacquer, topped by the surface layer. The DVD structure is a lot different. It actually consists of 2 polycarbonate discs glued together, each 0.6 mm thick. The data layer and the reflective metal layer are located right in the middle of the disc.

In a single-sided DVD, data is embedded into only one half of the disc, the other half being a dummy. However, DVDs can also be double-sided, with data embedded into both polycarbonate halves.

DVDs Holds More Information

The major difference between CDs and DVDs is the size of the pits and lands that encode data. DVD technology uses a much thinner laser, which results in smaller and narrower pits. This allows to pack more pits and lands onto surface of a DVD compared to a CD. Consequently, storage capacity for a CD is only 700 Mb, while for a basic, single-sided DVD it's about 4.7 Gb. DVD capacity can be further increased by writing data onto both sides of the disc and recording 2 data layers to each of those sides.

DVDs Have Faster Rotation Speeds

Another major difference is disc rotation speed. CDs have a maximum rotation speed of up to 500 rpm, while DVDs boast up to 1500 revolutions per minute. At greater rotation speed, the rate at which data can be read from or transferred onto the disc is much higher. These distinctions are key in deciding which of the two technologies best suits your needs.

DVDs, with their higher storage capacities and speedier data rates, are perfect for large, high quality video files. They are also a good fit for storing large amounts of data, such as music, document, and photo archives. Conversely, if you're dealing with relatively small amounts of data—under 700 Mb—a CD may be sufficient.

And this is it for our topic today, thank you for watching and for more information, please visit us at About.com.

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