Hard disks or hard drives are the most common internal data storage device for personal computers. They come in varying sizes, the largest holding terabytes of information. A terabyte is one thousand gigabytes, or about one trillion bytes. Using external hard disk drives to back up your data is a smart move. This way if the hard drive inside your computer fails for any reason, you can simply replace it with one of the external hard drives with no loss of data. Depending on the type of information you are backing up, multiple external hard drives in different locations may be necessary for critical or sensitive data.

There is an alternative way to backup your data if you do not have access to an external hard drive. You can backup your data with a virtual hard drive. A virtual hard drive (VHD) is the virtual correspondent of an internal hard drive in a physical machine. VHDs are run by websites; some are free and others require payment to use their services. There are also websites that offer large amounts of file space for a fee; this is a particularly convenient way to back up your data.