What is the distinction between the virtualization approach advocated by Xen and the style of
microkernel advocated by the Exokernel project? In your answer, highlight two things they have
in common and two distinguishing characteristics between the approaches.

What will be an ideal response?

Both approaches are examples of virtualization in the general sense of the word, offering abstraction over the
underlying hardware.
They also both support the coexistence of a number of virtual machines on one physical architecture (and
also the necessary isolation between instances), through domains in the case of virtualization and operating
system emulations in the case of microkernels.
They do operate at different levels though. System virtualization is concerned with providing
virtualization over the hardware, preserving the interface as provided by the hardware. In contrast,
microkernels provide a much higher level of abstraction based on offering (typically policy neutral) operating
system services (for example address spaces, threads and interprocess communication on a single machine).
The emphasis in system virtualization is on extremely lightweight implementation, hence the interest in
techniques such as paravirtualization, and hence system virtualization can support potentially very large
numbers of virtual machines compared to the microkernel approach.
The use cases of system virtualization are also quite different, for example managing the mapping of
services to virtual machines in server farms (exploiting the ability to migrate virtual images).