The most common problem experienced with hard disk drives are:

• Software corruption.
This is caused when a program has crashed and taken with it some important information that the drive and file structures need to operate properly. The best solution here is to use a program like Symantec's 'The Norton Utilities' (Mac or PC), or a similar product to detect if the file structure and the integrity of the files are still in tact. Running a program like this periodically can eliminate most software corruption problems.

• Bad Blocks.
Bad blocks are quite common and occur when either the drive has been dropped or shaken when running or simply when a small particle of dust has been trapped by the magnetic head and damaged a small spot on the surface of the hard drive platter. This is often called a crash and with it comes the realization that the file that was written on that small spot may no longer be valid. The best thing to do is to test the drive on a regular basis. Products such as Symantec's 'The Norton Utilities' allow you to test the drive for bad blocks without destroying your data.

• Fragmentation.
This will not so much create a problem with drive reliability, as it will in performance. As you use a drive and copy, erase, and re-copy files to it, you create fragmentation. In other words the drive will copy files into whatever area is available on the drive, even if that area is not contiguous. This fragmentation causes the heads to have to move farther and take longer than they would if the file was contiguous. De-fragmentation programs are available and are part of most good drive maintenance programs like Symantec's 'Norton Utilities' (Mac or PC).

• Viruses.
This is quickly becoming one of the most common reasons for system crashes. It is a good idea to use an anti-virus program to eliminate the potential damage that can occur due to viruses. The best thing to do is to be very careful when copying programs from friends or the Internet.