89 lines
2.9 KiB
Groff
89 lines
2.9 KiB
Groff
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.TH FD 4
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.SH NAME
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fd \- floppy disk
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.SH DESCRIPTION
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The
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.B fd*
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devices refer to the Floppy disk driver using the NEC PD765 floppy disk
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controller. These diskettes are arrays of 512 byte sectors, although Minix
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always works with two sectors at a time due to its 1024 byte block size. You
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can read or write any number of bytes however, Minix takes care of cutting
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and pasting incomplete blocks together.
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.PP
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The driver is normally configured for two floppy disk devices
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.B fd0
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and
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.BR fd1 .
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It can handle two more, but it is unlikely that the average PC can.
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.PP
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On the first access to an
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.B fd
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device (by
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.BR open (2)
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or
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.BR mount (2)),
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the driver will execute a series of read tests to determine the floppy type.
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This works ok for all floppy types except the true 360k type, because it
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is indistinguishable from the 720k type. This only means that the size of
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the floppy is not estimated right.
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.PP
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Bits 2\-6 of the minor device number may be set to the floppy disk type
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to make it known to the driver what type of diskette it is reading or
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writing. The non-auto devices should be used for formatting, or when one wants to
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be absolutely sure that the device is accessed right. These devices exist for
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drive 0:
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.sp
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.nf
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.ta +4n +7n +9n +8n
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type device minor media
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.ta +5n +7n +9n +7n
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0 fd0 0 autodetect
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1 pc0 4 360k, 5.25"
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2 at0 8 1.2M, 5.25"
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3 qd0 12 360k in a 720k, 5.25" drive
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4 ps0 16 720k, 3.5"
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5 pat0 20 360k in a 1.2M, 5.25" drive
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6 qh0 24 720k in a 1.2M, 5.25" drive
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7 PS0 28 1.44M, 3.5"
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.fi
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.DT
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.PP
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Type 4 may also be used for the rarely seen 720k, 5.25" floppies (type 2 made
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them obsolete fast.) Note that these "types" only describe the floppies from
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a software point of view, type 1 and 4 drives use the same parameters.
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.PP
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If the format bit (bit 7) is set, then the driver interprets write commands
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as track formatting requests. This is used by the
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.BR format (1)
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command.
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.PP
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If the type bits are set to 28, 29, 30, or 31, then the driver uses a
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partition table found in sector 0 to partition the floppy. The partitions
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of
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.B fd0
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may be accessed as
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.B fd0p0
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through
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.BR fd0p3 .
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See
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.BR controller (4)
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for a description of the partition table, and associated ioctl commands.
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.SH FILES
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/dev/fd[0\-3], /dev/pc[0\-3], /dev/at[0\-3], /dev/qd[0\-3], /dev/ps[0\-3],
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/dev/pat[0\-3], /dev/qh[0\-3], /dev/PS[0\-3], /dev/fd[0\-3]p[0\-3]
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.SH "SEE ALSO"
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.BR format (1),
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.BR controller (4),
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.BR part (8).
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.SH BUGS
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The driver does not know the size of a 360k diskette in a 360k 5.25"
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drive, because it uses the 720k parameters for it. So it will happily try
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to read past the end making all kinds of interesting noises. It's a good
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thing these drives are practically obsolete.
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.PP
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The partition table is only read when the drive motor is off and only for
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an auto or partition device. The driver assumes that a floppy in a drive
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with a running motor can't have been replaced all of a sudden.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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