What is the difference between virtualization (virtualbox, etc.) and installation and use with hdd?

Question

virtual box

Good evening!
What is the difference between virtualization (virtualbox, etc.) and installation and use with hdd?
Do not consider the question stupid, I can not formulate it differently.
For example, Gentoo is running on virtualbox via win8, and Debian has a second OS installed on the hard drive. What restrictions can there be between them (in technical terms), or are they essentially the same thing?

Answer 1

At the moment, virtualization performance is close! to the performance of a bare axle on a machine. But it has a clear advantage associated with easy migration of the virtual machine. That's all