Pre-virtualization: uniting two worlds

Virtual machines are used in an increasingly varied set of application scenarios that favor different trade-offs. The virtual machine (VM) is an attractive solution, since it enables the use of the same operating systems across the scenarios, while permitting substitution of different hypervisors appropriate for the trade-offs. One of these scenarios is server consolidation, where a number of machines are replaced by VMs running on a single physical machine, increasing resource utilization. Another attractive scenario is the use of a VM to add features to an OS that contradict the design of the OS, such as enabling secure computing platforms with strictly controlled information flow. These two scenarios have dramatically different performance versus security trade offs, easily addressed by using different hypervisors.