Not very long ago, I was sent a cd by someone who
claimed she could not access a file she needed on one of her
personally made backup cds. No matter how many times she would try
copying the file to her desktop, she would get the same error,
informing her the file could not be copied due to some type of
corruption. She wanted to know if I could possibly help. I opened
the cd in my own cd-rom drive and tried copying the file she was
having a problem with and I realized it couldn't be copied on my
system either. Therefore, in all likelihood, it was the cd itself
that was problematic, not the system, player or other hardware. The
error received when trying to copy the file was a cyclic
redundancy check (CRC) error. In fact, this is the most common error
encountered with cd/dvd access or copying problems and I knew that
such a problem was often caused by a dirty or scratched disc, so I
examined the surface of the cd and just as I suspected, it was
marked. It had a distinct smudge print on it. I cleaned the whole
cd and after doing so, voila! , I was able to copy the needed file
from the cd to my hard drive.
her that the problem was fixed and when I told her it was just a
matter of cleaning the disc, she was surprised that the solution was
so simple and never thought such a confounding problem could be
caused by a less than pristine condition cd.
The fact is that cds and dvds can be very finicky. Just one speck of
dirt or a hairline scratch can cause problems in accessing your data
or the disc itself. These marks can make it difficult for the
drive's laser beam to properly read the disc. Fortunately, dirty
discs can be cleaned. Scratches can be more problematic, though, in
many cases they can be repaired.
With scratches, the severity of the
problem depends much on the type and location of the
scratch. Scratches that run across the disc or along the track, as
opposed to those that run in a straight line from rim to center, can
be the most difficult to repair.
These type of problems are unique to cd and dvd media because the
surfaces of the discs are bare and exposed, offering no protection
against dust, finger prints, smudge, dirt and scratches. An
exception is most dvd-ram discs which are encased in protective
cartridges. Hard drives are enclosed in a tough metal shell and even
cheap floppy discs are protected with a plastic cartridge.
It should be stated that most scratches and marks do not usually
affect playing a cd or dvd but when a problem accessing a cd or
file does occur, the reason is most often dirt or scratches on
crucial sections of the disc. For example, if the lead in area or
end points is damaged, you will most likely have problems accessing
the cd or dvd and receive the same CRC error as I did. Without
getting too technical, a Cyclic Redundancy Check (CRC) is a method
used to detect errors during file copying or transfer. When you
copy a file from your cd to your hard drive, the operating system
performs a CRC on a block of data on the cd and returns a
mathematical result - a number - known as a checksum which is used
to identify your file. When the checksums do not match, you get the
error and as a result, your file file cannot be copied or opened.
It can be a very frustrating experience. For more detailed
information on CRC. see here
CRC errors can also result from using low quality media which has
degraded over time. All cds and dvds degrade with time and use but
not all degrade at the same rate. If the data you need to store is
important, you should make a point to use quality cd and dvd media,
such as that made by Taiyo Yuden.
In general, the dye used on discs can affect
longevity. Media based on pthalocyanine are considered to have a
greater life expectancy than those based on cyanine. Standard media,
as made by well known, reputable manufacturers, i is said to have a
50 year life span. This may or may not apply to cheaper no name
Also, becoming more common now are
anti-scratch discs. TDK, for example, now manufactures, "armor
plated" dvd discs which they claim are virtually unscratchable and
have a life span of 100 years.
Kodak makes the Infoguard CD-R which they say
can last 100 years, as well.
Ok, so what to do if you can't play your cd or dvd or can't copy a
file from it. The first step, as you should now realize would be to
clean the disc.
Commercial cleaning fluids are best but I've
had good results just by running warm (not hot) tap water over the
disc and gently wiping and rinsing the disc clean. Make sure to use
a soft lint free cloth and never rub around the disc in circular
motions. Always wipe in straight lines from inside center to outside
rim. Then, wipe or pat dry.
Never use alcohol or abrasive household cleaners on cds or dvds.
They can damage the disc surface and most soap products can leave a
residue. If very dirty, a drop of dishwashing liquid (which rinses
clean with no residue) in a quart or so of water can be used.
For minor scratches that affect the ability to open or play your cds,
a dab of toothpaste can do wonders. Using a qtip or cotton
swab, gently polish a touch of toothpaste into the scratch to fill
and smooth it out Again, never wipe in a circular motion. Always
clean from center to rim. Then rinse under warm tap water. An
alternative to toothpaste that may also help is petroleum jelly
(Vaseline) Just a tiny touch of it to smooth out the scratches and
then rinse with warm water.
If home remedies don't solve the problem, you can try a commercial
scratch repair kit. Some effective ones can be seen here:
But before rushing out to buy one of these kits without knowing if
you'll be wasting your money or not, I would advise an attempt to
copy the bad disc to a new disc first. . I've had success doing this
by using the trial program CDClone to copy a
badly scratched problem disc to a new one.
I would also recommend trying ISO Buster which is highly regarded
and totally free. It may allow you to extract the bad cd contents to
your hard drive or mount the bad cd for copying to a new cd.
More info here
If copying doesn't work, there are certain programs you can try that
may help you recover data right from the damaged disc itself. One
that is very good and also free is CD Check. Even if a complete
recovery isn't possible, it may be able to recover a file
partially. It works on all the major PC systems from Windows 95 and
up and is especially good for CRC errors.
It can be downloaded here:
Another excellent program for corrupt disc recovery is Bad Copy Pro
which works not only on cd/dvd media, but floppies and zipdisks.
For more information and to download a free evaluation copy of the
program see here:
In closing, it should also be noted that some cd/dvd players are
better than others when it comes to their ability to handle
scratched or defective discs. If you have plenty of scratched discs
and frequent problems playing them, you might want to consider a new
cd/dvd-rom drive that is known to excel in reading bad media. Check
out CDRLabs for reviews and pay particular attention to the cd/dvd
error correction tests.