During this time, James listened to a lot of music and was always frustrated by the wear and tear of his phonograph records. He was also unsatisfied with their sound quality. So, one Saturday while he was home alone, he started sketching out a better music recording system. James wanted a system that would record and replay songs without physical contact between its parts, and he saw the best way to do it would be by using light. He was familiar with digital data recording, in punch card or magnetic tape form. He knew that if you could represent the binary 0 and 1 with dark and light, then a device could be produced that is able to read sounds or any other information without wearing it out and if he could make the binary compact enough he could store a bunch on a small piece of film.
Bettelle let him pursue his project and in 1970, after years of work, he succeeded in inventing the first digital-to-optical recording and playback system, the CD.
A CD is a simple round piece of plastic about 4/100ths of an inch thick, and 12 centimeters in diameter used for electronic recording, storing, and playback. Most of a CD consists of an injection-moulded piece of clear polycarbonate plastic. During manufacturing, this plastic
Vicky Lile 12SG
is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data circling from the inside of the disc to the outside. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is put onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it, and the CD label is printed onto the acrylic. The compact disc was first used for audio storage only, but are now used to store audio, video, text, and any other information in digital form, and are able to hold 783 megabytes in all.
The CD works, because binary information is encoded in light and dark forms on the disk. Laser light is shone on to the disk and the reflection from either the light or dark parts of the CD produces an electric signal. Once this information is converted into electric signals its easy to convert to audio or visual signals. The CD player finds and reads the data stored as bumps on the CD. The drive consists of three fundamental components:
- A drive motor, which spins the disk and will rotate between 200 and 500 rpm depending on which track is being read. As the laser moves outward, it rotates slower so the bumps travel past the laser at a constant speed, and the data comes off at a constant rate.
- A laser, and a lens system that focuses in on and reads the bumps.
- A tracking mechanism, which moves the laser assembly so that the laser’s beam can follow (and be centered on) the spiral track. The tracking system has to be able to move the laser at micro resolutions. It has to continually move outward from the center of the disc.
The job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects the changes in light. The bumps reflect light differently to the rest of the aluminum layer, and the opto-electronic sensor detects that change in light. The electronics in the drive interpret the changes in reflection and reads the bits.
Through the 1970s he continued to refine the CD-ROM (Compact Disc Read-Only Memory), which is an adaptation of the CD that is designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound. It can be read (but not written) by a computer using a CD-ROM drive. At first, potential investors and even scientists were skeptical about long-term applications and profits. It wasn't until 1980
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that Russell's company, Battelle, first licensed his system; and it was 1985 before major electronics corporations like Philips and Sony bought manufacturing rights and began mass production of the Compact Disk.
There are many good things that have been prompted by the invention of the CD; thanks to the CD, we are able to bring a variety of music with us while relaxing or on the go, without taking up a lot of space. Without CDs, we wouldn’t have computer games, or software. We also spend less money now, because not only does the CD have an almost faultless quality, as they can survive finger marks, small scratches, and water, and there’s no contact between the disc and the what’s reading it, so the CD lasts longer. From the CD, came the CD-ROM, CD-I (an interactive CD that’s used to store video, audio or data), CD-ROM XA (a CD that contains computer data, compressed audio data, and video/picture data) photo and video CDs, CD-R (a writeable CD that can only be written to once), and the CD-RW (a re-writeable CD that can be written many times). We can now store our own music, documents, and other files onto a disk, which is seen in both good and bad ways, but either way, the CD has brought a lot more convenience to our present world.
resources-
- www.howstuffworks.com
- www.inventors.about.com
- hutchinson multimedia enyclopedia
- Microsoft Encarta 98 Encyclopedia
www.ec.gc.ca/acidrain
Penguin Publishing House, 1987 , Pearce Fred Acid Rain. What is it and what is it doing to us?
