How does cd burning work

Insert a CD into your CD drive. Need more help? Join the discussion. A subscription to make the most of your time. Try one month free. Was this information helpful? Yes No. Thank you! Any more feedback? The more you tell us the more we can help. Can you help us improve? Resolved my issue. Clear instructions. Easy to follow. No jargon. Pictures helped.

Didn't match my screen. Incorrect instructions. Too technical. When the disc is blank, the dye is translucent : Light can shine through and reflect off the metal surface. But when you heat the dye layer with concentrated light of a particular frequency and intensity, the dye turns opaque : It darkens to the point that light can't pass through.

Instead, the disc has a dye layer underneath a smooth, reflective surface. On a blank CD-R disc, the dye layer is completely translucent, so all light reflects. The write laser darkens the spots where the bumps would be in a conventional CD, forming non-reflecting areas. By selectively darkening particular points along the CD track, and leaving other areas of dye translucent, you can create a digital pattern that a standard CD player can read.

The light from the player's laser beam will only bounce back to the sensor when the dye is left translucent, in the same way that it will only bounce back from the flat areas of a conventional CD. So, even though the CD-R disc doesn't have any bumps pressed into it at all, it behaves just like a standard disc. A CD burner's job, of course, is to "burn" the digital pattern onto a blank CD. In the next section, we'll look inside a burner to see how it accomplishes this task.

In the last section, we saw that CD burners darken microscopic areas of CD-R discs to record a digital pattern of reflective and non-reflective areas that can be read by a standard CD player.

Since the data must be accurately encoded on such a small scale, the burning system must be extremely precise. Still, the basic process at work is quite simple. The CD burner has a moving laser assembly, just like an ordinary CD player.

But in addition to the standard "read laser," it has a "write laser. Read lasers are not intense enough to darken the dye material, so simply playing a CD-R in a CD drive will not destroy any encoded information. The write laser moves in exactly the same way as the read laser: It moves outward while the disc spins. The bottom plastic layer has grooves pre-pressed into it, to guide the laser along the correct path.

By calibrating the rate of spin with the movement of the laser assembly, the burner keeps the laser running along the track at a constant rate of speed. To record the data , the burner simply turns the laser writer on and off in synch with the pattern of 1s and 0s. The laser darkens the material to encode a 0 and leaves it translucent to encode a 1. Most CD burners can create CDs at multiple speeds. At 1x speed, the CD spins at about the same rate as it does when the player is reading it.

This means it would take you about 60 minutes to record 60 minutes of music. At 2x speed, it would take you about half an hour to record 60 minutes, and so on.

For faster burning speeds, you need more advanced laser-control systems and a faster connection between the computer and the burner. You also need a blank disc that is designed to record information at this speed. In addition to this wide compatibility , CD-Rs are relatively inexpensive. The main drawback of the format is that you can't reuse the discs. Once you've burned in the digital pattern, it can't be erased and re-written. In the mid '90s, electronics manufacturers introduced a new CD format that addressed this problem.

CD-R discs hold a lot of data, work with most CD players and are fairly inexpensive. But unlike tapes , floppy disks and many other data-storage mediums, you cannot re-record on CD-R disc once you've filled it up. CD-RW discs have taken the idea of writable CDs a step further, building in an erase function so you can record over old data you don't need anymore.

These discs are based on phase-change technology. In CD-RW discs, the phase-change element is a chemical compound of silver, antimony, tellurium and indium. As with any physical material, you can change this compound's form by heating it to certain temperatures. When the compound is heated above its melting temperature around degrees Celsius , it becomes a liquid; at its crystallization temperature around degrees Celsius , it turns into a solid.

In a CD-RW disc, the reflecting lands and non-reflecting bumps of a conventional CD are represented by phase shifts in a special compound. When the compound is in a crystalline state, it is translucent, so light can shine through to the metal layer above and reflect back to the laser assembly.

When the compound is melted into an amorphous state, it becomes opaque, making the area non-reflective. In phase-change compounds , these shifts in form can be "locked into place": They persist even after the material cools down again.

If you heat the compound in CD-RW discs to the melting temperature and let it cool rapidly, it will remain in a fluid, amorphous state, even though it is below the crystallization temperature. In order to crystallize the compound, you have to keep it at the crystallization temperature for a certain length of time so that it turns into a solid before it cools down again. In the compound used in CD-RW discs, the crystalline form is translucent while the amorphous fluid form will absorb most light.

On a new, blank CD, all of the material in the writable area is in the crystalline form, so light will shine through this layer to the reflective metal above and bounce back to the light sensor. To encode information on the disc, the CD burner uses its write laser , which is powerful enough to heat the compound to its melting temperature.

These "melted" spots serve the same purpose as the bumps on a conventional CD and the opaque spots on a CD-R: They block the "read" laser so it won't reflect off the metal layer.

Each non-reflective area indicates a 0 in the digital code. Every spot that remains crystalline is still reflective , indicating a 1. As with CD-Rs, the read laser does not have enough power to change the state of the material in the recording layer -- it's a lot weaker than the write laser. The erase laser falls somewhere in between: While it isn't strong enough to melt the material, it does have the necessary intensity to heat the material to the crystallization point.

By holding the material at this temperature, the erase laser restores the compound to its crystalline state, effectively erasing the encoded 0. This clears the disc so new data can be encoded. Some newer drives and players, including all CD-RW writers, can adjust the read laser to work with different CD formats. For the most part, they are used as back-up storage devices for computer files.

As we've seen, the reflective and non-reflective patterns on a CD are incredibly small, and they are burned and read very quickly with a speeding laser beam. In this system, the chances of a data error are fairly high. In the next section, we'll look at some of the ways that CD burners compensate for various encoding problems. In the previous sections, we looked at the basic idea of CD and CD-burner technology.

Using precise lasers or metal molds, you can mark a pattern of more-reflective areas and less-reflective areas that represent a sequence of 1s and 0s. The system is so basic that you can encode just about any sort of digital information.

There is no inherent limitation on what kind of mark pattern you put down on the disc. But in order to make the information accessible to another CD drive or player , it has to be encoded in an understandable form. This format was specifically designed to minimize the effect of data errors.

This is accomplished by carefully arranging the recorded data and mixing it with a lot of extra digital information. On the next page, you'll learn about the extra information encoded on a burned CD.

The actual arrangement of information on music CDs is incredibly complex. And CD-ROMS -- compact discs that contain computer files rather than song tracks -- have even more extensive error-correction systems. In a regular mass-produced CD, data is stored as binary data in a series of physical pits and flat areas or a lack of pits in a special layer on the disc. To read a CD, a CD player shines a laser along a spiral groove embedded in the data layer of the disc.

Instead, you could embed a transparent chemical layer in the disc that would darken when heated with a higher-powered laser. Get it? In , a typical desktop hard drive stored 20 or 40 megabytes, and a CD-ROM could hold megabytes. And only a few years after that, you could buy bulk CD-Rs in spindles for pennies a disc. Much to the chagrin of every industry that published data on CDs, people used CD-Rs for piracy too —both in commercial counterfeit operations and also personal use, and the rapidly dropping price of CD-R media fueled that trend considerably.

People began to use them as one-time disposable methods of transferring data between computers, and younger people in particular often used them to make custom audio mix CDs.