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Compact Disks
Amusingly, some people think that compact disks are "indestructible". They
certainly are compared to vinyl phonograph records, and are in fact much more hardy than
conventional magnetic media, which is one big reason for their rise in popularity.
However, they are far from immune to damage, and have their own special care concerns that
do not apply to media like floppy disks. Recordable CDs, including CD-R and CD-RW media,
are even more delicate than regular pressed CDs and must be treated with great care.
The following are general care guidelines for compact disk media:
- Temperature: Compact disks, in my experience, should not be subjected to
temperatures exceeding about 100 degrees Fahrenheit. They are made of plastic, and will
very easily warp if left in direct sunlight. Any warping of a disk effectively makes it
useless. CDs can be exposed to very low temperatures, but they should be allowed to acclimate to room temperature before using. Disks burned
using CD-R drives are even more sensitive to temperature and are best kept as close to
room temperature as possible.
- Contact: The less handling that is done of the compact disk, the better. Unlike
floppy disks, which have all or most of the media surface protected by an external jacket,
the CD has the entire media area exposed, and thus vulnerable. This is one reason why CD
systems that use caddies prolong the life of CDs--they in essence form a
"jacket" for the CD that protects it. Handling CDs causes dirt and scratches
that can eventually interfere with reading. CDs should be handled by the edge or the inner
hub whenever possible.
- Labeling: You should in general not put stickers, labels or tape
on CDs, or write on them with regular pens, etc. The only exception would be labeling kits
specifically designed for CDs. Abusing the label side of the disk can damage the data
layer, which is right under the top surface. This is especially true of CD-R disks, which
should only be written upon with a soft, felt-tip marker, preferably in the designated
spaces on the top surface of the disk.
- Moisture: CDs are made of plastic, so they basically laugh off moisture. Spill
coffee on a CD? No problem. Rinse it in warm water, wipe it with a soft cloth, good as
new. Try that with a floppy disk! (Actually, don't. :^) ) Mind you, CD-R disks are better
off not being exposed to liquids.
- Magnetic Fields: Compact disks encode information non-magnetically. They are
wholly unaffected by magnetic fields.
- Flexibility: CDs are rigid and will tolerate very little in the way of flexing.
They can be bent five or ten degrees, but beyond this they run the risk of cracking or
breaking altogether.
 Warning: Bending a CD until it
breaks can be dangerous. You might expect it to snap clean into two pieces, but in my
experience a CD excessively bent can in fact practically shatter, sending shards of rather
sharp plastic flying in many directions.
- Dust and Dirt: Compact disks are not read by direct contact with the read lens of
the CD-ROM drive, so can deal with accumulated dirt and dust much better than floppy
disks, for example. Excessive buildup will eventually impair operation, but disks are
easily cleaned (see below).
- Cleaning: Compact disks can be cleaned effectively, but this should be done in
the correct manner. CDs should always be cleaned radially, which means starting at the
inside of the disk and moving outward, not by rubbing in circles. In other words,
you would clean it the way you would clean the spokes of a bicycle wheel. The reason for
this is that cleaning in circles can cause long scratches over a single section of the
data track, which will cause signal loss. Small scratches across many tracks can easily be
handled by the error-correcting capabilities of the drive.
Cleaning is best done using a simple cloth, with perhaps a bit of warm water if necessary.
That's it. Remember that this is plastic, and many solvents and cleaners will damage
plastics. I have never found a need to use specialized CD cleaning kits. Never clean the
label side of a disk; that can lead to more damage than you might expect, because the data
is actually recorded right under the label of the disk.
- Scratch Repair: Scratches can actually be repaired on CDs using special kits that
essentially polish them out of the bottom of the disk. This might be surprising to some;
wouldn't doing this remove part of the information that is stored on the disk? The reason
it doesn't is that the actual pits and lands that encode the information on the CD are not
on the underside of the disk, the surface that is read by the lens. They are stamped into
the top of the CD, right under the label. This is what gives CDs some immunity to
scratches and dirt; if the data were on the bottom surface a single scratch would cause a
great deal of problems.
- Airport X-Ray Machines: Compact disks are not adversely affected by X-ray machines at airports...
See this section on media and storage life.
 Next: Airport X-Ray Machines
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