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In 2000, one of the biggest news stories was the rise of Napster and similar file-sharing programs. With these programs, you could get an MP3 version of just about any song you want without shelling out a dime. The record companies were fairly upset over this turn of events, and understandably so: They weren't making any money off the distribution of their product to millions of people.
An external writable CD drive, also called a CD burner: With this type of drive, you can take music or data files from your computer and make your own CDs.
But there was money to be made on the "Napster revolution," as electronics manufacturers and retailers soon discovered. In 1999, 2000 and early 2001, sales of CD burners and blank CD-Recordable discs skyrocketed. Suddenly it was feasible for the average person to gather songs and make their own CDs, and music-mix makers everywhere wanted to get their hands on the means of production. Today, writable CD drives (CD burners) are standard equipment in new PCs, and more and more audio enthusiasts are adding separate CD burners to their stereo systems. In less than five years, CDs have eclipsed cassette tapes as the mix medium of choice.
In this edition of HowStuffWorks, you'll find out how CD burners encode songs and other information onto blank discs. We'll also look at CD re-writable technology, see how the data files are put together and find out how you can make your own music mixes with a CD burner.
A CD has a long, spiraled data track. If you were to unwind this track, it would extend out 3.5 miles (5 km).
If you've read How CDs Work, you understand the basic idea of CD technology. CDs store music and other files in digital form -- that is, the information on the disc is represented by a series of 1s and 0s (see How Analog and Digital Recording Works for more information). In conventional CDs, these 1s and 0s are represented by millions of tiny bumps and flat areas on the disc's reflective surface. The bumps and flats are arranged in a continuous track that measures about 0.5 microns (millionths of a meter) across and 3.5 miles (5 km) long. To read this information, the CD player passes a laser beam over the track. When the laser passes over a flat area in the track, the beam is reflected directly to an optical sensor on the laser assembly. The CD player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD player recognizes this as a 0.
A CD player guides a small laser along the CD's data track. In conventional CDs, the flat areas, or lands, reflect the light back to the laser assembly, while the bumps deflect the light so it does not bounce back.
The bumps are arranged in a spiral path, starting at the center of the disc. The CD player spins the disc while the laser assembly moves outward from the center of the CD. At a steady speed, the bumps move past any point at the outer edge of the CD more rapidly than they move past any point nearer the CD's center. In order to keep the bumps moving past the laser at a constant rate, the player must slow the spinning speed of the disc as the laser assembly moves outward.
The CD player spins the disc while moving the laser assembly outward from the middle. To keep the laser scanning the data track at a constant speed, the player must slow the disc as the assembly moves outward.
At its heart, this is all there is to a CD player. The execution of this idea is fairly complicated, because the pattern of the spiral must be encoded and read with incredible precision, but the basic process is pretty simple.
In the next section, you'll find out how data is recorded on CDs, both by professional equipment and the home CD burner. Light Write
In the last section, we saw that conventional CDs store digital data as a pattern of bumps and flat...