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Caring for Optical Media Chapter <strong>13</strong><br />
775<br />
performance because the laser focuses on a point inside the actual disc, but dirt or deep scratches can<br />
interfere with reading a disc.<br />
To remedy this type of problem, you can clean the bottom surface of the CD with a soft cloth, but be<br />
careful not to scratch the surface in the process. The best technique is to wipe the disc in a radial<br />
fashion, using strokes that start from the center of the disc and emanate toward the outer edge. This<br />
way, any scratches will be perpendicular to the tracks rather than parallel to them, minimizing the<br />
interference they might cause. You can use any type of solution on the cloth to clean the disc, so long<br />
as it will not damage plastic. Most window cleaners are excellent at removing fingerprints and other<br />
dirt from the disc and don’t damage the plastic surface.<br />
If your disc has deep scratches, they can often be buffed or polished out. A commercial plastic cleaner<br />
such as that sold in auto parts stores for cleaning plastic instrument cluster and tail-lamp lenses is<br />
very good for removing these types of scratches. This type of plastic polish or cleaner has a very mild<br />
abrasive that polishes scratches out of a plastic surface. Products labeled as cleaners usually are<br />
designed for more serious scratches, whereas those labeled as polishes are usually milder and work<br />
well as a final buff after using the cleaner. Polishes can be used alone if the surface is not scratched<br />
very deeply.<br />
Most people are careful about the bottom of the disc because that is where the laser reads, but the top<br />
is actually more fragile! This is because the lacquer coating on top of the disc is very thin, normally<br />
only 6–7 microns (0.24–0.28 thousandths of an inch). If you write on a disc with a ball point pen, for<br />
example, you will press through the lacquer layer and damage the reflective layer underneath, ruining<br />
the disc. Also, certain types of markers have solvents that can eat through the lacquer and damage the<br />
disc as well. You should write on discs only with felt tip pens that have compatible inks, such as the<br />
Sharpie or Staedtler Lumocolor brand, or other markers specifically sold for writing on CDs. In any<br />
case, remember that scratches or dents on the top of the disc are more fatal than those on the bottom.<br />
Read errors can also occur when dust accumulates on the read lens of your CD-ROM drive. You can<br />
try to clean out the drive and lens with a blast of “canned air” or by using a drive cleaner (which can<br />
be purchased at most music stores that sell audio CDs).<br />
If your discs and your drive are clean, but you still can’t read a particular disc, your trouble might be<br />
due to disc capacity. Many older CD-ROM drives are unreliable when they try to read the outermost<br />
tracks of newer discs where the last bits of data are stored. You’re more likely to run into this problem<br />
with a CD that has lots of data—including some multimedia titles. If you have this problem, you<br />
might be able to solve it with a firmware or driver upgrade for your CD-ROM drive, but the only solution<br />
might be to replace the drive.<br />
Sometimes too little data on the disc can be problematic as well. Some older CD-ROM drives use an<br />
arbitrary point on the disc’s surface to calibrate their read mechanism, and if there happens to be no<br />
data at that point on the disc, the drive will have problems calibrating successfully. Fortunately, this<br />
problem usually can be corrected by a firmware or driver upgrade for your drive.<br />
Many older drives have had problems working under Windows 9x. If you are having problems, contact<br />
your drive manufacturer to see whether a firmware or software-driver upgrade is available that<br />
might take care of your problem. With new high-speed drives available for well under $100, it might<br />
not make sense to spend any time messing with an older drive that is having problems. It might be<br />
more cost-effective to upgrade to a new drive instead.<br />
If you are having problems with only one particular disc and not the drive in general, you might find<br />
that your difficulties are in fact caused by a defective disc. See whether you can exchange the disc for<br />
another to determine whether that is indeed the cause.