All major Internet companies use virtualization« to host their data. It is the only way to have many servers with little overhead without the large space for housing single OS run Servers.VMWare
Companies like Facebook« receive 100 servers every week in their Data Centers«. However, that is not 100 physical servers but 100 virtual servers or VMs. They typically have 10 VMs running on a single server, with 10 servers per rack.
« is one of the top companies for virtualization applications. With their ESXi
« suit, you can run VMs from a home-brewed network environment to a larger scaled corporate infrastructure.