Virtualization is about running an Operating System (the guest OS) on the top of another OS (the host OS). This technique enables running several virtual machines with different OSes at the same time on the same hardware. VMWare, MacOnLinux, and Xen are examples of virtualizer software.

Virtualization requires guest OSes to be built for the host machine processor. It should not be confused with emulation, that do not have this requirement: When an OS runs on the top of a virtualizer, its code runs unchanged on the processor, whereas an emulator has to interpret to the guest OS code. MAME or Basilisk are examples of emulators.

Binary compatibility is another different feature: it is the ability of an OS to run applications from another OS. For instance BSD systems are able to run Linux binaries.

Manuel Bouyer is a NetBSD developer who has been involved in kernel hacking for many years. He recently added support for Xen to NetBSD, based on Christian Limpach's work for the Xen team

In this interview, Manuel will tell us what is so good with Xen, and what was the work required to have it working on NetBSD.