When it comes to hosting, cloud architecture refers to using an independent server for each and every part of the Internet hosting service. Such a setup results in better performance because one machine will be used just for file storage, a different one just for running databases, etcetera, therefore different system processes will not run on the very same machine. The latter will reduce the probability of system errors significantly and will allow your sites to work faster, not mentioning the better uptime. When you are looking for this kind of service, you need to double check that you'll really find it as a lot of companies advertise cloud web hosting packages, however the control panels they use aren't designed to function in a true cloud and can work only on one server. The issue with using a single machine is that in case one service crashes or generates high load, the entire server will almost certainly go offline, so your sites will no longer be accessible.