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><A
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>Floppies</A
></H1
><P
>A floppy disk consists of a flexible membrane covered on one
or both sides with similar magnetic substance as a hard disk.
The floppy disk itself doesn't have a read-write head, that is
included in the drive. A floppy corresponds to one platter in
a hard disk, but is removable and one drive can be used to
access different floppies, whereas the hard disk is one
indivisible unit.</P
><P
>Like a hard disk, a floppy is divided into tracks and sectors
(and the two corresponding tracks on either side of a floppy
form a cylinder), but there are many fewer of them than on a
hard disk.</P
><P
>A floppy drive can usually use several different types of disks;
for example, a 3.5 inch drive can use both 720 kB and
1.44 MB disks. Since the drive has to operate a bit differently
and the operating system must know how big the disk is, there
are many device files for floppy drives, one per combination of
drive and disk type.
Therefore, <TT
CLASS="FILENAME"
>/dev/fd0H1440</TT
> is the first floppy drive (fd0),
which must be a 3.5 inch drive,
using a 3.5 inch, high density disk (H) of
size 1440 kB (1440), i.e., a normal 3.5 inch HD floppy.
For more information on the naming conventions for the floppy
devices, see XXX (device list).</P
><P
>The names for floppy drives are complex, however, and Linux
therefore has a special floppy device type that automatically
detects the type of the disk in the drive. It works by
trying to read the first sector of a newly inserted floppy
using different floppy types until it finds the correct one.
This naturally requires that the floppy is formatted first.
The automatic devices are called <TT
CLASS="FILENAME"
>/dev/fd0</TT
>,
<TT
CLASS="FILENAME"
>/dev/fd1</TT
>, and so on.</P
><P
>The parameters the automatic device uses to access a disk can
also be set using the program \cmd{setfdprm}. This can be
useful if you need to use disks that do not follow any usual
floppy sizes, e.g., if they have an unusual number of sectors,
or if the autodetecting for some reason fails and the proper
device file is missing.</P
><P
>Linux can handle many nonstandard floppy disk formats
in addition to all the standard ones. Some of these require
using special formatting programs. We'll skip these disk
types for now, but in the mean time you can examine the
<TT
CLASS="FILENAME"
>/etc/fdprm</TT
> file. It specifies the settings
that <B
CLASS="COMMAND"
>setfdprm</B
> recognizes.</P
><P
>The operating system must know when a disk has been changed in
a floppy drive, for example, in order to avoid using cached
data from the previous disk. Unfortunately, the signal line
that is used for this is sometimes broken, and worse, this won't
always be noticeable when using the drive from within MS-DOS.
If you are experiencing weird problems using floppies, this might
be the reason. The only way to correct it is to repair the
floppy drive.</P
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