When few of us used multiple PCs, keeping track of our digital lives was relatively simple. Personal or work files were instantly accessible and easy to back up, and since there was only a single copy we knew it was always the latest version.

But today most of us use more than one machine, so keeping track of files and folders is much more difficult. How can PC users get the latest version of their data, wherever they are, and ensure that a lost or failed device does not mean lost data? One solution is online storage-based services, such as Carbonite, Xdrive, Box.net, iBackup, MediaMax or Amazon’s S3. These allow users to upload data to a centralised online data vault, valuable protection over and above local back-ups on an external hard drive. But if the user is offline, the data are not normally available and some services can cause sluggish PC performance.