fd - floppy disk device


Floppy drives are block devices with major number 2. Typically they are owned by root.floppy and have either mode 0660 (access checking via group membership) or mode 0666 (everybody has access). For the following devices, n is the drive number. It is 0 for the first drive, 1 for the second etc. To get a minor number for a specific drive connected to the first controller, add n to the minor base number. If it is connected to the second controller, add n+128 to the minor base number. Warning: If you use formats with more tracks than supported by your drive, you may damage it mechanically. Trying once if more tracks than the usual 40/80 are supported should not damage it, but no warranty is given for that. Don’t create device entries for those formats to prevent their usage if you are not sure.

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:


fd special files access the floppy disk drives in raw mode. The following ioctl(2) calls are supported by fd devices:

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 re-enable 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 manual page for floppycontrol.


The various formats allow one to read and write many types of disks. However, if a floppy is formatted with a too small inter sector gap, performance may drop, up to 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.




Alain Knaff (Alain [AT], David Niemi (niemidc [AT], Bill Broadhurst (bbroad [AT]


floppycontrol(1), mknod(1), chown(1), getfdprm(1), superformat(1), mount(8), setfdprm(1)