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. AVI format. DVDs are typically quite inexpensive, and they cost even less when bought in bulk. The cost of these storage media has fallen rapidly throughout the late s and early s, and continues to become more affordable as manufacturing costs diminish.
The burner allows this storage medium to become even more flexible than before. Initially, the acronym "DVD" was supposed to stand for digital video disc , but because it can hold any type of data, not just video, members of the inter-corporation DVD Forum refer to it as a digital versatile disc. These are called "dash. Check the speed rating. The speed rating listed on a disc is the amount of time it will take to burn the DVD. Open your DVD burning software.
Select the DVD burner you wish to use when prompted. Select the type of files you wish to burn when prompted.
The icon will change to a Burn symbol. Click OK to burn. After burning your first CD or DVD, insert it into another computer and open a file or two to verify that you have completed the process correctly. Nothing would be worse than losing your files, only to learn that you don't have a good backup either.
Click to Do Nothing with it, instead of the other options it offers. Continue to select and add files from other locations on your hard drive. If you only need the one copy, click Finish.
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