FD

Section: Linux Programmer's Manual (4)
Updated: 2020-08-13
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NAME

fd - floppy disk device  

CONFIGURATION

Floppy drives are block devices with major number 2. Typically they are owned by root:floppy (i.e., user root, group floppy) and have either mode 0660 (access checking via group membership) or mode 0666 (everybody has access). The minor 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 controller. In the following device tables, n represents the drive number.

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:

NameBase
minor #

fdn0

5.25 inch double-density device files:

NameCapacityCyl.Sect.HeadsBase
KiBminor #

fdnd36036040924

5.25 inch high-density device files:

NameCapacityCyl.Sect.HeadsBase
KiBminor #

fdnh360360409220
fdnh4104104110248
fdnh4204204210264
fdnh720720809224
fdnh8808808011280
fdnh12001200801528
fdnh144014408018240
fdnh147614768218256
fdnh149414948318272
fdnh160016008020292

3.5 inch double-density device files:

NameCapacityCyl.Sect.HeadsBase
KiBminor #

fdnu360360809112
fdnu720720809216
fdnu80080080102120
fdnu104010408013284
fdnu112011208014288

3.5 inch high-density device files:

NameCapacityCyl.Sect.HeadsBase
KiBminor #

fdnu360360409212
fdnu720720809216
fdnu8208208210252
fdnu8308308310268
fdnu144014408018228
fdnu1600160080202124
fdnu168016808021244
fdnu172217228221260
fdnu174317438321276
fdnu176017608022296
fdnu1840184080232116
fdnu1920192080242100

3.5 inch extra-density device files:

NameCapacityCyl.Sect.HeadsBase
KiBminor #

fdnu288028808036232
fdnCompaQ28808036236
fdnu3200320080402104
fdnu3520352080442108
fdnu3840384080482112
 

DESCRIPTION

fd special files access the floppy disk drives in raw mode. The following ioctl(2) calls are supported by fd devices:
FDCLRPRM
clears the media information of a drive (geometry of disk in drive).
FDSETPRM
sets the media information of a drive. The media information will be lost when the media is changed.
FDDEFPRM
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.
FDGETDRVTYP
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.
FDFLUSH
invalidates the buffer cache for the given drive.
FDSETMAXERRS
sets the error thresholds for reporting errors, aborting the operation, recalibrating, resetting, and reading sector by sector.
FDSETMAXERRS
gets the current error thresholds.
FDGETDRVTYP
gets the internal name of the drive.
FDWERRORCLR
clears the write error statistics.
FDWERRORGET
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.
FDTWADDLE
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.
FDSETDRVPRM
sets various drive parameters.
FDGETDRVPRM
reads these parameters back.
FDGETDRVSTAT
gets the cached drive state (disk changed, write protected et al.)
FDPOLLDRVSTAT
polls the drive and return its state.
FDGETFDCSTAT
gets the floppy controller state.
FDRESET
resets the floppy controller under certain conditions.
FDRAWCMD
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 floppycontrol(1) manual page.  

FILES

/dev/fd*  

NOTES

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.  

SEE ALSO

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

COLOPHON

This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.


 

Index

NAME
CONFIGURATION
DESCRIPTION
FILES
NOTES
SEE ALSO
COLOPHON