(what are these boxes?)
There are different types of virtualization. This topic primarily focuses on 'machine' virtualization - a VM that runs within a container on some type of virtualization engine (Hyper-V, XenServer, ESX, Virtual Server, VirtualPC, Parallels, etc.). Another dominant type of virtualization is session virtualization - this is where Remote Desktop Services (Terminal Services) falls into place. Another type of virtualization is not new but has been slow to gain hold is application virtualization (App-V and XenApp Streamed applications are good examples).
For everything dealing with machine virtualization (e.g. Backup and Restore, Security, Availability, etc) you usually have to choose among two approaches. The first one is: “Treat every VM as it was just an ordinary piece of hardware”. This approach is typical for infrastructures that have just started adopting virtualization or decided to stop with very limited virtualization penetration. It has the following pros and cons.
The second approach is: “Take advantages of advanced Virtualization features and offload as many jobs to hypervisor (or its management partition) as you can”. This is typical for infrastructures with higher virtualization penetration and strong trust to their hypervisor of choice. This approach has the following pros and cons.