dection 5Storage Devices.docx

The track widths you are seeing here are exaggerated

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The track widths you are seeing here are exaggerated to get the point across. In reality, they're much smaller than this. While this narrow track allows a DVD to store more data than a CD, it also causes some problems with the DVD. The wide track on a CD allows room for air. When a CD is being read in the CD drive, as long as the read laser hit somewhere within this track, it will be able to read data and the optical drive will work like it's supposed to. But in DVDs the room for error is smaller because the track is narrow. The read laser has to be aimed precisely at the track. If it's not or if there's any distortion or problems with the DVD like unbalance in the disc causing it to wobble as it spins, it could cause the laser to miss this track. If this happens, the disc cannot read the data properly. There're actually a variety of different types of DVDs that you can use in your computer system. Let's take a look at each of these beginning with the DVD-ROM, and then we'll look at a DVD-RW on dual layers. DVD-ROM 2:04-2:52 If you want to store computer data on a DVD, you'll need to use a DVD-ROM. A DVD-ROM is really just a big CD-ROM. It holds 4.7 gigabytes of data and is read-only memory. This disk has been created in a DVD production facility and cannot be written to. You can only read from it. DVDs are rated according to the speed by which they can read data from the optical disk. But the numbers used to rate DVD drive speeds are different than those used to rate CD drive speeds. The speed of a DVD drive is measured by multiples of 11 megabits per second. For example, 1x DVD drive can transfer data at 11 megabits per second. A 2x DVD drive, therefore, can transfer data at 22 megabits per second. An 18x DVD drive can transfer data at 198 megabits per second. DVD-RW 2:53-3:54 If you want to have a rewritable DVD format, then you can use a DVD-RW. With a DVD-RW disc, you can erase and rewrite data to it. A DVD-RW disc can hold 4.7 gigabytes of data, so it's like having a removable hard drive. It is a little slower than a hard drive, but it has the same rewrite capabilities as a hard drive, and it's portable. Just like a CD-RW, a DVD-RW uses a crystal coating on the bottom of the DVD disc. When the write laser and the DVD-RW drive hits it, it causes a crystal to form which reflects light. This creates the reflective and non-reflective areas on the bottom of the DVD-RW disc, allowing us to encode binary computer data. DVD-RW discs have a limited lifetime. A DVD-RW disc can be written and rewritten up to 1,000 times depending upon the quality of the disc. Beyond that you may start to see errors. The disc lifetime can be shortened by how you handle the disc and the quality of the disc itself. The cheaper the disc, the fewer times you're going to be able to rewrite it.
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