| [9] | 1 | .TH FD 4
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| 2 | .SH NAME
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| 3 | fd \- floppy disk
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| 4 | .SH DESCRIPTION
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| 5 | The
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| 6 | .B fd*
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| 7 | devices refer to the Floppy disk driver using the NEC PD765 floppy disk
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| 8 | controller. These diskettes are arrays of 512 byte sectors, although MINIX 3
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| 9 | always works with two sectors at a time due to its 1024 byte block size. You
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| 10 | can read or write any number of bytes however, MINIX 3 takes care of cutting
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| 11 | and pasting incomplete blocks together.
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| 12 | .PP
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| 13 | The driver is normally configured for two floppy disk devices
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| 14 | .B fd0
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| 15 | and
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| 16 | .BR fd1 .
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| 17 | It can handle two more, but it is unlikely that the average PC can.
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| 18 | .PP
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| 19 | On the first access to an
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| 20 | .B fd
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| 21 | device (by
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| 22 | .BR open (2)
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| 23 | or
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| 24 | .BR mount (2)),
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| 25 | the driver will execute a series of read tests to determine the floppy type.
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| 26 | This works ok for all floppy types except the true 360k type, because it
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| 27 | is indistinguishable from the 720k type. This only means that the size of
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| 28 | the floppy is not estimated right.
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| 29 | .PP
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| 30 | Bits 2\-6 of the minor device number may be set to the floppy disk type
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| 31 | to make it known to the driver what type of diskette it is reading or
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| 32 | writing. The non-auto devices should be used for formatting, or when one wants to
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| 33 | be absolutely sure that the device is accessed right. These devices exist for
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| 34 | drive 0:
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| 35 | .sp
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| 36 | .nf
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| 37 | .ta +4n +7n +9n +8n
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| 38 | type device minor media
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| 39 | .ta +5n +7n +9n +7n
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| 40 | 0 fd0 0 autodetect
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| 41 | 1 pc0 4 360k, 5.25"
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| 42 | 2 at0 8 1.2M, 5.25"
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| 43 | 3 qd0 12 360k in a 720k, 5.25" drive
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| 44 | 4 ps0 16 720k, 3.5"
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| 45 | 5 pat0 20 360k in a 1.2M, 5.25" drive
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| 46 | 6 qh0 24 720k in a 1.2M, 5.25" drive
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| 47 | 7 PS0 28 1.44M, 3.5"
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| 48 | .fi
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| 49 | .DT
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| 50 | .PP
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| 51 | Type 4 may also be used for the rarely seen 720k, 5.25" floppies (type 2 made
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| 52 | them obsolete fast.) Note that these "types" only describe the floppies from
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| 53 | a software point of view, type 1 and 4 drives use the same parameters.
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| 54 | .PP
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| 55 | If the format bit (bit 7) is set, then the driver interprets write commands
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| 56 | as track formatting requests. This is used by the
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| 57 | .BR format (1)
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| 58 | command.
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| 59 | .PP
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| 60 | If the type bits are set to 28, 29, 30, or 31, then the driver uses a
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| 61 | partition table found in sector 0 to partition the floppy. The partitions
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| 62 | of
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| 63 | .B fd0
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| 64 | may be accessed as
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| 65 | .B fd0p0
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| 66 | through
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| 67 | .BR fd0p3 .
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| 68 | See
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| 69 | .BR controller (4)
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| 70 | for a description of the partition table, and associated ioctl commands.
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| 71 | .SH FILES
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| 72 | /dev/fd[0\-3], /dev/pc[0\-3], /dev/at[0\-3], /dev/qd[0\-3], /dev/ps[0\-3],
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| 73 | /dev/pat[0\-3], /dev/qh[0\-3], /dev/PS[0\-3], /dev/fd[0\-3]p[0\-3]
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| 74 | .SH "SEE ALSO"
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| 75 | .BR format (1),
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| 76 | .BR controller (4),
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| 77 | .BR part (8).
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| 78 | .SH BUGS
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| 79 | The driver does not know the size of a 360k diskette in a 360k 5.25"
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| 80 | drive, because it uses the 720k parameters for it. So it will happily try
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| 81 | to read past the end making all kinds of interesting noises. It's a good
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| 82 | thing these drives are practically obsolete.
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| 83 | .PP
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| 84 | The partition table is only read when the drive motor is off and only for
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| 85 | an auto or partition device. The driver assumes that a floppy in a drive
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| 86 | with a running motor can't have been replaced all of a sudden.
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| 87 | .SH AUTHOR
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| 88 | Kees J. Bot (kjb@cs.vu.nl)
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