RX(4)               UNIX Programmer's Manual                RX(4)



NAME
     rx - dual-density floppy disk

DESCRIPTION
     The files /d_e_v_/*r_x_* access the RX02 double-density floppy
     drive.  R_x_0_l_ is drive 0, at low density; changing l to h
     switches to high density, swapping 1 for 0 references the
     other drive.

     The r_x_* files are traditional UNIX block devices; reads and
     writes may be of any size and need not be sector-aligned.
     Raw access is provided by r_r_x_*; reads and writes to these
     files must be multiples of a UNIX block (512 bytes) and
     start on a block boundary.

     Both r_x_* and r_r_x_* use the DEC standard sector mapping algo-
     rithm.  This ignores the first track, and skips roughly six
     sectors between accesses.  See DEC documentation for further
     info.  The `really raw' files r_r_r_x_* bypass the mapping algo-
     rithm; they treat the disk as a contiguous array of physical
     sectors.

     One i_o_c_t_l_ function is available:

          ioctl(fd, RIOCINI, 0);

     will initialize a diskette.  The density to use is taken
     from the file opened; eg, to set drive 1 to double-density,
     do

          fd = open("/dev/rrx1h", 1);
          ioctl(fd, RIOCINI, 0);

     Only one open is allowed on a given drive at a given time.

BUGS
     The restriction to a single open makes it messy to construct
     a filesystem on a floppy, as many maintenance programs such
     as m_k_f_s_ and f_s_c_k_ open the device twice.  Given the security
     problems inherent in user-mounted filesystems, and the non-
     portable nature of the format, this isn't a big problem; we
     just don't let people do it.













Printed 6/15/82                HEP                              1