Data transfer means transferring data from one hard drive to another. This is usually done when you purchase a new computer and want to transfer your documents/data from your old computer to it, or when you want to make a complete clone/copy of a drive for a new system or backup drive. The only limit on the amount of data transferred is the capacity of your new drive.

If your hard drive is making noise, make sure you get your data off it (transferred to new drive or backed up) before it dies. Once it's completely dead, it'll cost you hundreds or thousands of dollars to recover your data.