Storing files online is increasingly popular, particularly as a secondary backup of data archived on companies' on-site servers. Here are three of the best services for storing data in the ether.

MOZY

Mozy offers 2GB of online backup free, enough to store a few hundred songs or tens of thousands of pages of text. For $4.95 a month, you get unlimited backup of your personal computer files. Mozy Pro allows you to back up everything on your company's servers for $6.95 a month, plus 50 cents per gigabyte.

IDRIVE

IDrive also offers 2GB of free backup, or up to 150GB for $4.95 a month. The service can simultaneously back up data online and to an external drive, which saves the trouble of setting up a second automatic backup application. It can also back up data from your phone.

SOS ONLINE BACKUP

SOS is more expensive, costing $19.95 a year for 2GB of storage and $49.95 a year for 15GB, with no free level. But unlike Mozy or IDrive, it automatically backs up files whenever they are changed, even if they are open. It also saves each version of a file indefinitely, until you delete it.