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: Name Base minor # fdn 0 5.25 inch double density device files: Name Capac. Cyl. Sect. Heads Base minor # fdnd360 360K 40 9 2 4 5.25 inch high density device files: Name Capac. Cyl. Sect. Heads Base minor # fdnh360 360K 40 9 2 20 fdnh410 410K 41 10 2 48 fdnh420 420K 42 10 2 64 fdnh720 720K 80 9 2 24 fdnh880 880K 80 11 2 80 fdnh1200 1200K 80 15 2 8 fdnh1440 1440K 80 18 2 40 fdnh1476 1476K 82 18 2 56 fdnh1494 1494K 83 18 2 72 fdnh1600 1600K 80 20 2 92 3.5 inch double density device files: Name Capac. Cyl. Sect. Heads Base minor # fdnu360 360K 80 9 1 12 fdnu720 720K 80 9 2 16 fdnu800 800K 80 10 2 120 fdnu1040 1040K 80 13 2 84 fdnu1120 1120K 80 14 2 88 3.5 inch high density device files: Name Capac. Cyl. Sect. Heads Base minor # fdnu360 360K 40 9 2 12 fdnu720 720K 80 9 2 16 fdnu820 820K 82 10 2 52 fdnu830 830K 83 10 2 68 fdnu1440 1440K 80 18 2 28 fdnu1600 1600K 80 20 2 124 fdnu1680 1680K 80 21 2 44 fdnu1722 1722K 82 21 2 60 fdnu1743 1743K 83 21 2 76 fdnu1760 1760K 80 22 2 96 fdnu1840 1840K 80 23 2 116 fdnu1920 1920K 80 24 2 100 3.5 inch extra density device files: Name Capac. Cyl. Sect. Heads Base minor # fdnu2880 2880K 80 36 2 32 fdnu3200 3200K 80 40 2 104 fdnu3520 3520K 80 44 2 108 fdnu3840 3840K 80 48 2 112
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 re-enable 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 manual page for floppycontrol.
The various formats allow 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@linux.lu), David Niemi (firstname.lastname@example.org), Bill Broadhurst (email@example.com).
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