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(fdutils.info)Disk organisation

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How disks are organized
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   All floppies have two levels of _formatting_, both of which must be
known in order to read them.  The first is the _binary_ or _sector_
level format, which is how raw data is stored on the disk.  The second
is a higher level organization, often called a _file system_, which
allows multiple files to be conveniently stored on the disk.

   For example, a typical 1.44MB disk contains a low-level format, with
18 sectors per track, 80 tracks, and two sides (or heads); each sector
can hold 512 bytes of data for a total of 1474560 bytes (or 1440 KB).
When used under MS-DOS, this floppy would have a small portion of the
disk used to keep track of files on the disk (including a bootsector,
file allocation tables, directories, etc.).

   The floppy driver generally takes care of reading the binary, or
low-level format.  It can often "guess" the low-level disk geometry
needed to read the disk.  This is called autodetection (Note:
Autodetection).  If the driver can't autodetect the disk (e.g. if it
is in an unusual format) you can tell the driver what the geometry is
either by using the `setfdprm' (Note: setfdprm) utility or by using a
fixed geometry device device (e.g. `/dev/fd0H1440').

   Under Linux, many different file systems from many sources can be
used.  Some of these file systems are interpreted via a utility program
(for example `mtools' for using disks with an MS-DOS file system).  Many
file systems can alternatively be "mounted" to appear in the UNIX
directory structure until subsequently being unmounted; this is usually
implemented by having the kernel itself interpret the file system on the
disk.