Introduction to Virtualization - Oracle Solaris 10 System Virtualization Essentials - page 39

Additionally, a particular implementation may mimic a different operating sys-
tem if the two are sufficiently similar. In this case, the functionality of an OS ker-
nel can be represented by its system calls. A thin layer of software can translate
the system calls of the expected guest OS into the system calls of the hosting OS.
This strategy can allow programs and libraries compiled for one OS to run—un-
modified—in a VE that resides on a different OS, as long as they are all compiled
for the same hardware architecture.
The extra operations of translating one set of functionality to another will incur
a certain amount of CPU overhead, decreasing system performance. Achieving
identical functionality is usually challenging, but sufficient compatibility can be
achieved to enable common applications to run well.
1.2.3.3 Access to Hardware
OS virtualization features must allow isolated access to hardware so that one VE
can make appropriate use of hardware but cannot observe or affect another VE's
hardware accesses. Each VE might be granted exclusive access to a hardware re-
source, or such access might be shared. Existing implementations of OSV provide
differing functionality for hardware access.
Figure 1.21 shows most VEs sharing most of the CPUs and a network port. One
VE has exclusive access to another port and two dedicated CPUs.
Figure 1.21 Shared or Exclusive Hardware Assignments
1.2.3.4 Software Infrastructure
OSV design engineers decide exactly where to place the division between base OS
operations and VEs. A VE may include only the application processes or, alterna-