.TH RX 4 HEP
.SH NAME
rx \- dual-density floppy disk
.SH DESCRIPTION
The files
.IR /dev/ \(** rx \(**
access the RX02
double-density floppy drive.
.I Rx0l
is drive 0,
at low density;
changing
.B l
to
.B h
switches to high density,
swapping
.B 1
for
.B 0
references the other drive.
.LP
The
.IR rx \(**
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
.IR rrx \(**;
reads and writes to these files
must be multiples of a
.SM UNIX
block
(512 bytes)
and start on a block boundary.
.LP
Both
.IR rx \(**
and
.IR rrx \(**
use the DEC standard sector mapping algorithm.
This ignores the first track,
and skips roughly six sectors between accesses.
See DEC documentation for further info.
The `really raw' files
.IR rrrx \(**
bypass the mapping algorithm;
they treat the disk as a contiguous array of physical sectors.
.LP
One
.I ioctl
function is available:
.IP
.B "ioctl(fd, RIOCINI, 0);"
.LP
will initialize a diskette.
The density to use
is taken from the file opened;
eg,
to set drive 1 to double-density,
do
.LP
.nf
	fd = open("/dev/rrx1h", 1);
	ioctl(fd, RIOCINI, 0);
.fi
.LP
Only one open is allowed
on a given drive
at a given time.
.SH BUGS
The restriction to a single open
makes it messy to construct
a filesystem on a floppy,
as many maintenance programs
such as
.I mkfs
and
.I fsck
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.