Some people believe that optical discs and drives are indestructible when compared to their magnetic counterparts. Actually, modern optical drives are far less reliable than modern hard disk drives. Reliability is the bane of any removable media, and CD-ROMs and DVD-ROMs are no exceptions.

By far the most common causes of problems with optical discs and drives are scratches, dirt, and other contamination. Small scratches or fingerprints on the bottom of the disc should not affect performance because the laser focuses on a point inside the actual disc, but dirt or deep scratches can interfere with reading a disc.

To remedy this type of problem, you can clean the bottom surface of the CD with a soft cloth, but be careful not to scratch the surface in the process. The best technique is to wipe the disc in a radial fashion, using strokes that start from the center of the disc and emanate toward the outer edge.

This way, any scratches will be perpendicular to the tracks rather than parallel to them, minimizing the interference they might cause. You can use any type of solution on the cloth to clean the disc, so long as it will not damage plastic. Most window cleaners are excellent at removing fingerprints and other dirt from the disc and don't damage the plastic surface.

If your disc has deep scratches, they can often be buffed or polished out. A commercial plastic cleaner such as that sold in auto parts stores for cleaning plastic instrument cluster and tail-lamp lenses is very good for removing these types of scratches.

This type of plastic polish or cleaner has a very mild abrasive that polishes scratches out of a plastic surface. Products labeled as cleaners usually are designed for more serious scratches, whereas those labeled as polishes are usually milder and work well as a final buff after using the cleaner.

Polishes can be used alone if the surface is not scratched very deeply. The Skip Doctor device made by Digital Innovations can be used to make the polishing job easier. Most people are careful about the bottom of the disc because that is where the laser reads, but the top is actually more fragile!

This is because the lacquer coating on top of the disc is very thin, normally only 6–7 microns (0.24–0.28 thousandths of an inch). If you write on a disc with a ball point pen, for example, you will press through the lacquer layer and damage the reflective layer underneath, ruining the disc.

Also, certain types of markers have solvents that can eat through the lacquer and damage the disc as well. You should write on discs only with felt tip pens that have compatible inks, such as the Sharpie or Staedtler Lumocolor brand, or other markers specifically sold for writing on CDs.

In any case, remember that scratches or dents on the top of the disc are more fatal than those on the bottom. Read errors can also occur when dust accumulates on the read lens of your CD-ROM drive. You can try to clean out the drive and lens with a blast of "canned air" or by using a drive cleaner (which can be purchased at most stores that sell audio CDs).

If your discs and your drive are clean, but you still can't read a particular disc, your trouble might be due to disc capacity. Many older CD-ROM drives are unreliable when they try to read the outermost tracks of newer discs where the last bits of data are stored.

You're more likely to run into this problem with a CD that has lots of data—including some multimedia titles. If you have this problem, you might be able to solve it with a firmware or driver upgrade for your CD-ROM drive, but the only solution might be to replace the drive.

Sometimes too little data on the disc can be problematic as well. Some older CD-ROM drives use an arbitrary point on the disc's surface to calibrate their read mechanism, and if there happens to be no data at that point on the disc, the drive will have problems calibrating successfully.

Fortunately, this problem usually can be corrected by a firmware or driver upgrade for your drive. Many older drives have had problems working under Windows 9x. If you are having problems, contact your drive manufacturer to see whether a firmware or software-driver upgrade is available that might take care of your problem.

With new high-speed drives available for well under $100, it might not make sense to spend any time messing with an older drive that is having problems. It might be more cost-effective to upgrade to a new drive (which won't have these problems and will likely be much faster) instead.

If you have problems reading a particular brand or type of disk in some drives but not others, you might have a poor drive/media match. Use the media types and brands recommended by the drive vendor.

If you are having problems with only one particular disc and not the drive in general, you might find that your difficulties are in fact caused by a defective disc. See whether you can exchange the disc for another to determine whether that is indeed the cause.