CD And DVD: Back from the Grave

Some CDs die gracefully, while others give up the ghost soon after being burned. How do you know which CDs are dying and, more importantly, what steps can be taken to recover data that appears to be lost? You could lie in bed worrying about it, or you could try these simple steps instead.

Checking discs

Fresh out of the burner, a disc may work fine, but a few years later - who knows? One solution is to check every single file on a CD manually. If you have a life, though, and would prefer to spend it doing more interesting things, then load up CDCheck. This handy utility will scan a CD and hunt down corrupt files. As an added bonus, the program is free.

It's a popular belief that little can be done to recover data from a CD or DVD. If the disc is in 10 pieces, that is true. However, it's not the end of the story if your CD is intact. The successful recovery of files from a problematic disc will depend on the severity and location of the damage. The critical zone is the inside track; this area contains important directory information about the file locations on the CD. Enough damage to this small area will make recovery impossible.

Start by checking the disc for obvious signs of dirt and damage. If the disc has cracks, there's an increased chance the CD will shatter in the drive, destroying the disc and probably your drive unit in the process (at 10,000 rpm, the outside of the disc is hitting 200km/h and this puts enormous stress on the disc). In these circumstances, there's little that can be done.

For discs with no obvious defects, clean the surface with a proper CD cleaning kit and follow the manufacturer's instructions. Don't use household cleaners. If this doesn't help, try the CD in a different drive. Newer high-speed CD drives can cause some CDs to stop working reliably, particularly if the disc has some minor damage. This happens because the disc is spinning too quickly for the data to be read accurately by the laser. Warping, scratches and other imperfections can exacerbate the problem. Remember that the original standard was 1x, and many new drives are rated higher than 50x.

An alternative is to use an older, slower drive or even a DVD burner - these tend to have slower CD reading speeds. Finally, some drive manufacturers ship handy utilities for slowing down the speed of a drive. For example, Plextor has a free utility suite called PlexTools that can be used to limit the CD speeds of its drives.

To correct physical damage like scratches on the underside of a disc, a simple polish can help. Many video stores and computer outlets will provide this service for about $8-$15.

Data recovery

If the techniques mentioned didn't help, it's time to try a data recovery tool and salvage what you can before binning the disc. One program designed for this task is CDCheck. Start by verifying the integrity of the files by clicking the Check button in the program and following the prompts. This will reveal which files are causing problems. If the errors are numerous and affect large files, the recovery process will take a long time - up to 48 hours or more for a badly-damaged full CD. Tweaking the recovery options will speed the process, but the number of salvaged files will probably fall. Don't fret, if the errors are few and involve smaller files, the total time will be closer to an hour or less.

To recover files using CDCheck, select the drive, click the Recover button and make any adjustments on the next menu as required. This process will copy the entire contents of the CD or DVD to your drive (both undamaged and recovered files), so make sure that you've got enough hard disk space free. The good news is that even if you don't get 100 per cent recovery of a file, it may still be usable. For example, many zip programs have a repair feature. Likewise, partially recovered TIFs and JPEGs can be fixed with a little cropping in your favourite graphics program. The images on this page illustrate the various recovery results from a test CD that had been deliberately damaged with a deep gouge.

Click here to see a screen shot of a flawlessly recovered file. Click here to see a screen shot of a slightly damaged jpeg that can be easilly fixed. Click here to see a screen shot of a picture with severe damage, or the "humpty dumpty"

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Scott Mendham

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