(3.50) inches (see figure 1-18). The platter is made of a
tough plastic that is coated with a magnetic oxide
material, allowing it to be magnetized. The inside of the
plastic jacket is lined with a soft wiping material that
continuously cleans the floppy disk as it spins within the
jacket. Look at figure 1-19; you will notice a hole in the
middle of the diskette. It is referred to as the center
hub. The hub makes it possible for the floppy disk
drive’s spindle to rotate the diskette inside the jacket.
The recording window allows the read-write head
mechanism of the floppy disk drive to come into contact
with the diskette so it can read from or write data onto
the diskette’s surface. Located just to the right of the
center hub is what we refer to as an index hole. This
index hole (and corresponding hole [or holes] in the
diskette), marks the first sector or starting point on the
diskette. The sectors on a diskette are controlled by
timing. On a soft-sectored diskette, the timing is
controlled by the software; therefore, only one timing
hole is needed on the diskette. On a hard-sectored
diskette, the timing is controlled by the hardware, and
the diskette has several timing holes.
Types of Floppies/Diskettes.— The diskettes you
will be using must be compatible with the floppy disk
drives on your microcomputer system. Diskettes can be
soft-sectored or hard- sectored. Depending upon the
disk drive’s characteristics, the disk drive can record
data on one side of the diskette or both and can record
data in one of several bit densities, depending upon how
the diskette is formatted.
When you are working with a soft-sectored
diskette, you must use your microcomputer and a utility
routine or program (in this case, a formatter program) to
sector or format each diskette for you.
On most
microcomputer systems, using the F O R M AT
command will automatically sector the diskette for you.
If you are working with hard-sectored diskettes,
then you need not format them. They have already been
presectored by the manufacturer for your specific
Figure 1-18.—Floppy disks/diskettes used on microcomputers.
Figure 1-19.—A typical 5.25-inch diskette.
microcomputer system. Floppy disk drives that use
hard-sectored diskettes read and write data faster.
However, the diskettes are more expensive and can only
be presectored (reformatted) for a specific system,
such as an IBM compatible or a Macintosh.
Most diskettes sold today are soil-sectored because
the wide range of microcomputers and their operating
systems vary considerably in respect to sectoring re-
quirements. For now, the important thing to remember
about sectoring is the fact that no matter what type of
diskette you are working with (soft- or hard- sectored),
it must be formatted before it is usable for storing data.
Storage Capacity.— Although diskettes are
relatively small in size, they can store a respectable
amount of data.
Some diskettes are single-sided,
single-density, whereas others are double-sided,
single-density; double-sided, double-density; or
double-sided, quad-density.
When we refer to a diskette as being double-sided,
double-density, what are we really saying? We are
saying the floppy disk drive is able to read from and
write to both sides of the diskette (hence, the term
double-sided), and that each sector on the disk can store
512 bytes of information (instead of the 256 bytes that
can be stored on a single-density diskette); hence, the
term double-density.
A diskette’s capacity is also
affected by the number of tracks per side. Therefore, if
you wanted to know the total storage capacity of a
double-sided, double-density diskette with 80 fifteen-
sector tracks per side, then you would use the following
formula to calculate the number of bytes:
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