Section: Linux Programmer's Manual (4)
fd - floppy disk device
Floppy drives are block devices with major number 2.
are owned by
(i.e., user root, group floppy) and have
either mode 0660 (access checking via group membership) or mode 0666
(everybody has access).
numbers encode the device type, drive number, and controller number.
For each device type (that is, combination of density and track count)
there is a base minor number.
To this base number, add the drive's
number on its controller and 128 if the drive is on the secondary
In the following device tables, n
Warning: if you use formats with more tracks
than supported by your drive, you may cause it mechanical damage.
Trying once if more tracks than the usual 40/80 are supported should not
damage it, but no warranty is given for that.
If you are not sure, don't create device
entries for those formats, so as to prevent their usage.
Drive-independent device files which automatically detect the media
format and capacity:
5.25 inch double-density device files:
5.25 inch high-density device files:
3.5 inch double-density device files:
3.5 inch high-density device files:
3.5 inch extra-density device files:
special files access the floppy disk drives in raw mode.
calls are supported by fd
clears the media information of a drive (geometry of disk in drive).
sets the media information of a drive.
The media information will be
lost when the media is changed.
sets the media information of a drive (geometry of disk in drive).
The media information will not be lost when the media is changed.
This will disable autodetection.
In order to reenable autodetection, you
have to issue an FDCLRPRM.
returns the type of a drive (name parameter).
For formats which work
in several drive types, FDGETDRVTYP returns a name which is
appropriate for the oldest drive type which supports this format.
invalidates the buffer cache for the given drive.
sets the error thresholds for reporting errors, aborting the operation,
recalibrating, resetting, and reading sector by sector.
gets the current error thresholds.
gets the internal name of the drive.
clears the write error statistics.
reads the write error statistics.
These include the total number of
write errors, the location and disk of the first write error, and the
location and disk of the last write error.
Disks are identified by a
generation number which is incremented at (almost) each disk change.
Switch the drive motor off for a few microseconds.
This might be
needed in order to access a disk whose sectors are too close together.
sets various drive parameters.
reads these parameters back.
gets the cached drive state (disk changed, write protected et al.)
polls the drive and return its state.
gets the floppy controller state.
resets the floppy controller under certain conditions.
sends a raw command to the floppy controller.
For more precise information, consult also the <linux/fd.h> and
<linux/fdreg.h> include files, as well as the
The various formats permit reading and writing many types of disks.
However, if a floppy is formatted with an inter-sector gap that is too small,
performance may drop,
to the point of needing a few seconds to access an entire track.
To prevent this, use interleaved formats.
It is not possible to
read floppies which are formatted using GCR (group code recording),
which is used by Apple II and Macintosh computers (800k disks).
Reading floppies which are hard sectored (one hole per sector, with
the index hole being a little skewed) is not supported.
This used to be common with older 8-inch floppies.
This page is part of release 5.02 of the Linux
A description of the project,
information about reporting bugs,
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