The behavior of an x-kernel running as a user task depends on the ``device drivers'' configured into the kernel. There are two categories of x-kernel device drivers: those that send real network packets (e.g., NIT in SunOS or IRIXETH in Irix), and those that send encapsulated network packets (e.g, SIMETH or SIMFDDI). Real-packet drivers use platform-specific methods to access network devices, and are relatively straightforward to configure and use. (Be sure to see the manual page for the individual drivers in Appendix A.)