mtools: geometry description
1
1 3.5.3 Disk Geometry Configuration
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1
1 Geometry information describes the physical characteristics about the
1 disk. Its has three purposes:
1
1 formatting
1 The geometry information is written into the boot sector of the
1 newly made disk. However, you may also describe the geometry
1 information on the command line. ⇒mformat, for details.
1
1 filtering
1 On some Unixes there are device nodes which only support one
1 physical geometry. For instance, you might need a different node
1 to access a disk as high density or as low density. The geometry
1 is compared to the actual geometry stored on the boot sector to
1 make sure that this device node is able to correctly read the
1 disk. If the geometry doesn't match, this drive entry fails, and
11 the next drive entry bearing the same drive letter is tried. ⇒
multiple descriptions, for more details on supplying several
1 descriptions for one drive letter.
1
1 If no geometry information is supplied in the configuration file,
1 all disks are accepted. On Linux (and on SPARC) there exist device
1 nodes with configurable geometry (`/dev/fd0', `/dev/fd1' etc), and
1 thus filtering is not needed (and ignored) for disk drives.
1 (Mtools still does do filtering on plain files (disk images) in
1 Linux: this is mainly intended for test purposes, as I don't have
1 access to a Unix which would actually need filtering).
1
1 If you do not need filtering, but want still a default geometry for
1 mformatting, you may switch off filtering using the `mformat_only'
1 flag.
1
1 If you want filtering, you should supply the `filter' flag. If you
1 supply a geometry, you must supply one of both flags.
1
1 initial geometry
1 On devices that support it (usually floppy devices), the geometry
1 information is also used to set the initial geometry. This initial
1 geometry is applied while reading the boot sector, which contains
1 the real geometry. If no geometry information is supplied in the
1 configuration file, or if the `mformat_only' flag is supplied, no
1 initial configuration is done.
1
1 On Linux, initial geometry is not really needed, as the
1 configurable devices are able to auto-detect the disk type
1 accurately enough (for most common formats) to read the boot
1 sector.
1
1 Wrong geometry information may lead to very bizarre errors. That's
1 why I strongly recommend that you add the `mformat_only' flag to your
1 drive description, unless you really need filtering or initial geometry.
1
1 The following geometry related variables are available:
1
1 `cylinders'
1 `tracks'
1 The number of cylinders. (`cylinders' is the preferred form,
1 `tracks' is considered obsolete)
1
1 `heads'
1 The number of heads (sides).
1
1 `sectors'
1 The number of sectors per track.
1
1 Example: the following drive section describes a 1.44M drive:
1
1 drive a:
1 file="/dev/fd0H1440"
1 fat_bits=12
1 cylinders=80 heads=2 sectors=18
1 mformat_only
1
1 The following shorthand geometry descriptions are available:
1
1 `1.44m'
1 high density 3 1/2 disk. Equivalent to: `fat_bits=12 cylinders=80
1 heads=2 sectors=18'
1
1 `1.2m'
1 high density 5 1/4 disk. Equivalent to: `fat_bits=12 cylinders=80
1 heads=2 sectors=15'
1
1 `720k'
1 double density 3 1/2 disk. Equivalent to: `fat_bits=12
1 cylinders=80 heads=2 sectors=9'
1
1 `360k'
1 double density 5 1/4 disk. Equivalent to: `fat_bits=12
1 cylinders=40 heads=2 sectors=9'
1
1 The shorthand format descriptions may be amended. For example, `360k
1 sectors=8' describes a 320k disk and is equivalent to: `fat_bits=12
1 cylinders=40 heads=2 sectors=8'
1