To understand why you need to use online backup services, consider the reasons why you should backup your data in the first place. The answers are obvious – to protect against hard disk failures, unintended deletions and other causes of data loss. Online backup services come in picture in the other causes.

The cheapest way to backup your data is to use external devices like CD/DVD or USB drives.
Let us consider the features of the external media currently available:

1. CD-ROM Disks: One of the cheapest backup media available, the CD can store about 700 MB of data. One can easily store data on a CD with the help of CD-writers which are common in most computers available today.
2. DVD-ROM Disks: These are a bit costlier than CDs but considering that one DVD disk can store 4.2 GB of data; the cost per GB is less as compared to CD.
3. USB Drive: Falling memory prices have made these backup media very cost effective. The additional advantage of these drives is that they can be reused many times unlike the CD/DVD. The only drawback is that usually a USB drive is required on the computer which may not be present in all computers.