This is outdated.
Because the microkernel does not provide filesystem support and other
features necessary to load the first system task from a storage medium,
the first task is loaded by the bootloader as a module to a specified
address. In the GNU system, this first program is the
executable. GNU Mach inserts the host control port and the device
master port into this task and appends the port numbers to the command
line before executing it.
serverboot program is responsible for loading and executing
the rest of the Hurd servers. Rather than containing specific
instructions for starting the Hurd, it follows general steps given in a
user-supplied boot script.
XXX More about boot scripts.