CS80 describe of /dev/rfd:
  controller:   0x8003  installed unit word
                   400  max instantaneous xfr rate (Kbytes/sec)
                     5  SS/80 integrated multi-unit controller
  unit:              1  generic device type (flexible or removable media)
                091531  device number (6 bcd digits)
                   256  # of bytes per block
                     1  # of blocks buffered
                     0  recommended burst size
                  5936  blocktime (microseconds)
                    45  continuous average transfer rate (Kbytes/sec)
                  4500  optimal retry time (centiseconds)
                  8400  access time parameter (centiseconds)
                    15  maximum interleave factor
                  0x00  fixed volume byte
                  0x01  removeable volume byte
  volume:           65  maximum cylinder address
                     0  maximum head address
                    15  maximum sector address
                  1055  maximum single-vector address
                     2  current interleave factor