Cloud computing is a fundamental change from how computers
and software have worked in the past. Traditionally, if you wanted to run an
application, you went out and bought a computer and software, set it up on your
own premises, and ran your program. You needed to pick out which operating
system you were going to run, handle the installation of your software, and
maintain your computer—keeping track of software upgrades, security, backups,
and so on.
Source of Information : Pragmatic - Code in the Cloud Programming Google App Engine 2011