Since I am writing the new 1Y0-A01 Citrix XenServer Enterprise Edition 4.0: Administration practice exam, I thought I'd write a quick post about what bare metal and hosted OS virtual solutions are, what the differences are between them, and the advantages and disadvantages of each.
Bare metal virtualization is running a virtual operating system on top of a hypervisor (a platform where multiple virtual operating systems can be run) which is sitting right on top of the hardware. Citrix XenServer and VMWare ESX Server are examples of bare metal virtual solutions.
Hosted OS virtualization is running a virtual operating system on top of virtual hardware on top of a host operating system, which is sitting on the physical hardware. Examples are VMWare GSX Server and Microsoft Virtual Server.
Of course, the obvious advantage to bare metal is that it is faster and more efficient, being that the OS is only two levels above the physical hardware. Some other advantages to bare metal are the scalability, enterprise features, and high data center availability. Disadvantages of bare metal solutions are that good ones are not going to be free and they do not run on user workstations.
Advantages to hosted OS solutions are that they are usually free software and can be run on user workstations. There are many disadvantages to hosted OS solutions. These include the OS licenses that are needed, it's slower than bare metal solutions, and the enterprise features are limited.
Like I said, just a quick overview of bare metal OS and hosted OS virtual solutions. A good place to start for more information is the hypervisor article at Wikipedia.
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