bo [/h] <unit>[,"<args>"]<unit><args>/h/h option is specified, bootstrap is loaded into
memory, and then control remains in the PDE instead of booting the
rest of the program. Once the bootstrap is loaded into memory and
contol is returned to the PDE, all of the PDE commands are available,
as well as the following control utilities:
^S -- Execute a single instruction.
^A -- Execute the code pointed to by the program counter.