In Tanenbaum’s Modern Operating Systems, fourth edition, about virtualization:
Are Virtualization without HW support, Virtualization with HW support, Paravirtualization, and Process virtualization exclusive between each other? (The way how the table is constructed seems to imply that.)
But I guess the first two are exclusive to each other, but each may overlap with the latter two (but I am not sure)?
How shall we understand the difference and relation between the four? Thanks.
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Paravirtualization means that the virtualized system knows that it is being virtualized and thus behaves differently than it would on real hardware, e.g. calling into the hypervisor instead of using some emulated device.
This is completely orthogonal to whether or not the (para-)virtualization is assisted by hardware. For example, Hyper-V with a normal guest is hardware-accelerated virtualization, Hyper-V with an “enlightened” guest is hardware-assisted paravirtualization.
Personally, I would not call Wine a virtualizer. Wine is an emulator. A virtualizer virtualizes something which is there, an emulator emulates something which is not there. Wine emulates the Windows ABI and API on Unix, where it does not exist. In fact, Wine orginally stood for “Windows Emulator”, the meaning was later changed to “Wine is not an emulator” to highlight the fact that it does not emulate the x86 ISA (unlike QEmu, for example), but it obviously still does emulate the Windows ABI and API.
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