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Minix/1.7.5/MANUALS/CAT4/FD.4

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+FD(4)                     Minix Programmer's Manual                      FD(4)
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+
+NAME
+     fd - floppy disk
+
+DESCRIPTION
+     The fd* devices refer to the Floppy  disk  driver  using  the  NEC  PD765
+     floppy  disk controller.  These diskettes are arrays of 512 byte sectors,
+     although Minix always works with two sectors at a time due  to  its  1024
+     byte  block  size.   You  can  read or write any number of bytes however,
+     Minix takes care of cutting and pasting incomplete blocks together.
+
+     The driver is normally configured for two floppy  disk  devices  fd0  and
+     fd1.  It can handle two more, but it is unlikely that the average PC can.
+
+     On the first access to an fd device (by open(2) or mount(2)), the  driver
+     will  execute  a series of read tests to determine the floppy type.  This
+     works ok for all floppy types except the true 360k type,  because  it  is
+     indistinguishable  from  the 720k type.  This only means that the size of
+     the floppy is not estimated right.
+
+     Bits 2-6 of the minor device number may be set to the floppy disk type to
+     make  it  known  to  the  driver  what  type of diskette it is reading or
+     writing.  The non-auto devices should be used for formatting, or when one
+     wants  to  be  absolutely  sure that the device is accessed right.  These
+     devices exist for drive 0:
+
+         type   device   minor   media
+          0      fd0      0      autodetect
+          1      pc0      4      360k, 5.25"
+          2      at0      8      1.2M, 5.25"
+          3      qd0      12     360k in a 720k, 5.25" drive
+          4      ps0      16     720k, 3.5"
+          5      pat0     20     360k in a 1.2M, 5.25" drive
+          6      qh0      24     720k in a 1.2M, 5.25" drive
+          7      PS0      28     1.44M, 3.5"
+
+     Type 4 may also be used for the rarely seen 720k, 5.25" floppies (type  2
+     made  them  obsolete  fast.)   Note  that these "types" only describe the
+     floppies from a software point of view, type 1 and 4 drives use the  same
+     parameters.
+
+     If the format bit (bit 7)  is  set,  then  the  driver  interprets  write
+     commands  as  track  formatting  requests.  This is used by the format(1)
+     command.
+
+     If the type bits are set to 28, 29, 30, or 31, then  the  driver  uses  a
+     partition  table  found  in  sector  0  to  partition  the  floppy.   The
+     partitions of fd0 may be accessed as fd0a through fd0d.  See hd(4) for  a
+     description of the partition table, and associated ioctl commands.
+
+FILES
+     /dev/fd[0-3],  /dev/pc[0-3],  /dev/at[0-3],  /dev/qd[0-3],  /dev/ps[0-3],
+     /dev/pat[0-3], /dev/qh[0-3], /dev/PS[0-3], /dev/fd[0-3][a-d]
+
+
+
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+
+
+                                                                             1
+
+
+
+FD(4)                     Minix Programmer's Manual                      FD(4)
+
+
+SEE ALSO
+     format(1), hd(4), part(8).
+
+BUGS
+     The driver does not know the size of a 360k  diskette  in  a  360k  5.25"
+     drive,  because  it  uses the 720k parameters for it.  So it will happily
+     try to read past the end making all kinds of interesting noises.  It's  a
+     good thing these drives are practically obsolete.
+
+     The partition table is only read when the drive motor is off and only for
+     an auto or partition device.  The driver assumes that a floppy in a drive
+     with a running motor can't have been replaced all of a sudden.
+
+AUTHOR
+     Kees J. Bot (kjb@cs.vu.nl)
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+                                                                             2
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