Real World Scenario 

The Virtual Infrastructure 3 (VI3) product holds a significant advantage over most other virtualization products because virtualization on VI3 does not require a host operating system. Products like VMware Server and Microsoft Virtual Server 2005 both require an underlying operating system to host the hypervisor.

The lack of the host operating system in VI3 offers additional stability and security. Without an underlying operating system like Windows, there is less concern for viruses, spyware, and unnecessary exposure to vulnerabilities.

With products like VMware Server (which require a host operating system), limitations from the host operating systems spill into the virtualization deployment. For example, installing VMware Server on Windows Server 2003 Web edition would establish two processors and 2GB of RAM limitations on VMware Server, despite its ability to use up to 16 processors and 64GB of RAM. At the same time, however, there's the advantage that hosted products have over the bare metal install of ESX Server. The existence of the host operating system greatly extends the level of hardware support on which the hypervisor will run. If the host operating system offers support, then the virtual machine will too. A great example of this hardware support is to look at the use of USB. ESX Server does not support USB, while VMware Server (and Workstation) includes support. Since the underlying host understands the USB technology, the virtual machines will also offer support.

In all, each of the virtualization products has its place in a network infrastructure. The Virtual Infrastructure 3 product is more suited to the mission-critical enterprise data center virtualization scenario, while the VMware Server product is best for noncritical test or branch office scenarios. And of course you cannot forget the best part of VMware Server: it's free!