Berlin - Duplicated data is often little more than dead weight on your hard drive.

To solve that problem, specialized programs are available to track them down and remove them. Nevertheless, experts advise using caution and security when using them, otherwise you might accidentally send some of your cherished family photos into digital limbo.

Digital photos are notorious for accumulating duplicates on a hard drive.

"It's easy to build up extra data if you make copies and then forget to delete the original," said Peter Knaak, a technology expert at Stiftung Warentest, a consumer reports organization.

"It's worth cleaning up the hard drive occasionally to free up memory space."

The Hamburg-based magazine Computer-Bild tested 12 programs for removing duplicate photos, music and other programs. Fee-based programs tended to be more successful than freeware alternatives.

EF Duplicate Files Manager 5.0 available from www. esoftare. de at a cost of 11.90 euros (18 dollars) was best at general data clean-up, with a practical approach that included looking for data clones in archives like zip files.

1-Klick Duplikate Loeschen 1.15 (19.95 euros from www. easy2sync. de) was best at tracking down duplicated e-mails and contacts in Outlook. It also allowed overlapping data sets to be combined into one contact.

Both programs had more functions than other alternatives and were simple to use. Users who want freeware should try Alldup 1.7 at www. allsync. de or MODupRemover 
1.11 at www. mobackup. de/moduplicateremover, according to Computer Bild.

All digital housecleaners operate on the same principles and compare data by its digital fingerprint. "The contents, including information like the name, format, size and date of creation, are compared," said Felix Leder, a computer scientist at the University of Bonn.

Leder says good programs can still perform even minute details such as meta information, change. Meta information is part of the digital fingerprint and includes data like the date and time. It can change although the contents of the data remain the same.

All tested programs were reliable at finding duplicates. But some caution is still required. Even the winner, "EF Duplicate Files Manager," did not recognize identical MP3 files with different ID3 tags as doubles.

Users should never let cleaning programs operate unsupervised and should always limit the parametres. "It speeds up the search while limiting it to files on the hard drive," says Leder.

But the speed also varies according to the program. In the test, Space Hound 4 (which cost around 30 euros and is available from www. fineware. com) an English-language program searched a 60 GB hard drive containing 25,000 files in six minutes, making it the fastest. But none of the programs needed more than half an hour to come up with its hit list.

Of course, the clean-up phase can take significantly longer than the search phase. Knaak advised users to take their time and exercise caution when deciding which files to erase. If you leave that decision to the program, you risk "eliminating programs you want to keep."

"It's also a good idea to make reference files so the program knows where the original files, that shouldn't be deleted, are," advises Leder. And there's one last rule.

"Never delete things if you don't know what they are." Getting rid of the wrong data coud cause your computer to crash.

INFO-BOX: Deleting data doubles

To make sure you do not delete files required for applications or the operating system, users should follow a few security guidelines, said Computer Bild. Avoid nasty surprises by making a complete data backup which is shielded from the search, otherwise they'll be considered duplicates.

The C:/Windows and C:/Programs folders, as well as data files labelled dll, inf, drv, ini, sys, lnk, or exe should also be protected from deletion. (dpa)