Berlin  - Unwanted files can cripple even speedy computers. Optimisation software promises to help, but in some cases it actually causes harm. It's often more effective to take out the data trash on your own.

"Many applications configure themselves to automatically start up when the operating system boots to look for updates," explains Peter Knaak, technology expert for the German consumer testing organisation Stiftung Warentest in Berlin. "That slows down the startup of Windows significantly."

Residual entries from deleted programs or device drivers in the registration database can also impede proper function, says Dirk Kuchel from Hamburg-based Computer Bild magazine. Many programs also leave behind files that were actually only needed temporarily for installation.

Fragmentation on the hard drive represents another problem: a computer stores data wherever it finds room on the hard drive - in many cases, breaking up the file into fragments to store it in a variety of locations.

"That means that hard drive will need longer to access the data than if it were stored in contiguous areas on the drive," explains Jaroslav Smycek, computer expert at the Consumer Central for Lower Saxony in Hanover, Germany.

So a periodic "spring cleaning" is required. A variety of optimisation programs promise to serve as a virtual maid, getting limping computers back up to speed with only a few mouse clicks. A roundup of nine products between 20 and 50 dollars recently tested in Computer Bild magazine paints a very different picture. Several Windows XP optimisers actually slowed down the start by one minute instead of speeding it up.

"The programs often aren't worth the price," is the judgment from Dirk Kuchel of "Computer Bild." Much of what the optimisers take over can also be handled by built-in functions in XP: this includes the deletion of unwanted files or making changes to settings hidden deep within the control panel. That said, this approach is not as convenient and requires experience. As Vista is more complex and stores temporary files in various locations, a utility program is the only way to go.

For tasks that cannot be handled by the user, several free tools come recommended. "CCleaner" (http://www.ccleaner.de) for cleaning the registration database is well known among experts. One current no-cost defragmenter is Disk Defrag (http://www.auslogics.com/disk-defrag).

Another factor to remember: changes to the registry "are akin to open heart surgery," Smycek emphasises. Making a back-up copy in advance is a must. If the cleaning operating fails for some reason, the operating system could suddenly stop working. That's why good optimisation programs always offer to make a back-up copy, Dirk Kuchel explains.

To prevent the computer from getting slower and slower, it's a good idea not to install every piece of new software you find, particularly if you are unlikely to use them all. While removing programs is fairly easy, those uninstallation processes leave residual elements and data flotsam, says Knaak from Stiftung Warentest. (dpa)