Paravirtualization (as an approach to run virtual machines) has been getting a lot of attention lately. The primary hypothesis is that paravirtualization makes the job of virtualization easier and more efficient than pure hardware virtualization.

There was a time and place where paravirtualization made sense, but that time has now passed. Let me explain why it is no longer a viable approach.

Paravirtualization (an idea orginally introduced by the Denali Project) proposes to modify a guest OS in order to redirect virtualization sensitive operations directly to the virtual machine monitor instead of trapping to it as done in pure hardware virtualization. Pure hardware virtualization is where hardware is completely virtualized and supports unmodified guest OSs.