The boot: prompt waits ten seconds for you to type advanced startup options.
If you don't type anything, the computer continues starting up normally. It
uses the kernel and configuration files on the startup device, which it also
uses as the root device.  Advanced startup options use the following syntax:

    <<device>kernel> <arguments>

For example, to start up from:
  the first SCSI device, type: sd()mach_kernel
  the b partition of the second IDE disk, type: hd(1,b)mach_kernel
  the floppy disk but use the SCSI disk as the root device, type:
    fd()mach_kernel rootdev=sd0a

If the computer won't start up properly, you may be able to start it up using
safe mode.  Type: -f

To continue starting up using standard options, press Return.