Xen is a virtual machine monitor which supports running multiple
guests operating systems on a single machine. Guest OSes (also
called "domains") require a modified kernel which supports Xen
hypercalls in replacement to access to the physical hardware. At
boot, the xen kernel is loaded along with the guest kernel for the
first domain (called domain0). domain0 has privileges to access
the physical hardware (PCI and ISA devices), administrate other
domains and provide virtual devices (disks and network) to other
domains.

This package contains the 4.2 Xen4 kernel itself.  PCI passthrough is
not supported.  PAE is mandatory; on i386 one must use XEN3PAE_DOM[0U].