PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

6.1 Diskette Types and Formats

Before a diskette can be used to
store data, you must prepare it by formatting it, although many
diskettes nowadays come preformatted. Formatting creates the physical
tracks and sectors that the drive uses to store data (called
low-level or physical
formatting) and the logical structure used by the
operating system to organize that data (called
logical or DOS formatting).
Unlike hard disks, which require two separate formatting passes, FDDs
perform both physical and logical formatting in one step. Also unlike
hard disks, diskettes do not need to be partitioned.

The Quick Format option available in Windows and later versions of DOS doesn't really format the diskette. It simply "zeros out" the File Allocation Tables and Root Directory entries, giving the appearance of a freshly formatted diskette but using the original format. Because data on diskettes fades with time, your data will be much safer if you do an actual format, which does a surface test and refreshes the physical and logical format structure of the diskette. Use Quick Format only on diskettes that have recently had a full format done on them. Also, do not count on a Quick Format to wipe sensitive data from a diskette. It's trivially easy to recover such data. To wipe data, do a full format on the diskette. Better yet, use a wipe utility, or bulk-erase the diskette. You have been warned.

To format a diskette with Windows,
right-click the drive icon in My Computer or Explorer, choose Format,
and mark the appropriate options. At the command line, format a
diskette by typing the command format a: /options,
where a: is the drive letter of the FDD, and
/options controls how the disk will be formatted.
The available options and the required syntax vary according to the
version of DOS or Windows you use. Type format /?
to display available formatting options. Which options are usable
depends upon both the FDD type and the diskette type. Some FDDs
accept only one type of diskette, while others accept two or more.

To format a diskette with Linux, run
kfloppy (the KDE Floppy Formatter, shown in Figure 6-1) or gfloppy, the Gnome
equivalent. Choose the appropriate size, filesystem, and other
options, and then click the Format button. If you prefer a command
line, mformat is convenient for formatting DOS
floppies. The mdir and mcopy
utilities are Linux equivalents for the DOS dir
and copy commands, but with additional features.

Figure 6-1. The KDE Floppy Formatter
avoids having to mount the diskette or remember command-line
options

For about a decade, the 3.5-inch High-Density (HD) FDD has been
standard. However, you may encounter older types of FDDs and
diskettes when upgrading an old machine or salvaging data, so
it's worth knowing something about these obsolescent
and obsolete formats. Table 6-1 lists the various
diskette formats that have been supported on the IBM platform over
the years.

In addition to the standard formats described in Table 6-1, Microsoft has used the proprietary
DMF (Distribution Media
Format) for some distribution diskettes. DMF increases the
capacity of a standard high-density 3.5-inch diskette by reducing the
inter-sector gap to allow 21 sectors/track rather than the standard
18 sectors/track, thereby expanding capacity to a true 1.64 MB
(usually called 1.68, 1.7, or 1.72 MB).

On most systems, you cannot read data from or write data to DMF
diskettes directly because DIR,
DISKCOPY, and other standard disk utilities do not
recognize DMF. In fact, attempting to use DISKCOPY
to copy a DMF diskette not only yields an unreadable target diskette,
but also may actually damage the DMF source diskette. DMF diskettes
are readable only by Setup and other Microsoft utilities designed to
work with CAB files (the compressed Cabinet files
used for software distribution), as well as by some third-party
utilities such as WinZip (http://www.winzip.com), which allows you to
extract data directly from compressed CAB files,
and WinImage (http://www.winimage.com), which allows you to
format and copy DMF diskettes directly.

Fortunately, most software is now distributed on CD or DVD discs, so
DMF diskettes are seldom used nowadays. We say fortunately because in
our experience DMF diskettes are much more likely than standard 1.44
MB diskettes to generate read errors. We have frequently found DMF
diskettes that were unreadable straight out of the box, and a DMF
diskette that is several years old is very likely to be unreadable. A
standard diskette was simply never intended to store that much data.

If you encounter an unreadable DMF diskette, we recommend using
WinImage to attempt to extract the CAB files manually to the hard
disk. If one FDD consistently generates read errors, the diskette may
be readable on a different drive, at least well enough to let you
extract the CAB files.