176
Apple
lie
Users
Handbook
Hard and Soft Sectoring
Locating a particular track
on
the
disk surface
is
a relatively
uncomplicated
matter
. The
drive
merely
moves
the
head
to
the
position
on
th
~
diskette
where
the
specified track
is
located,
much
like
the
needle
on
a
phonograph
is
positioned
to
the
location
of
a specific song
on
a record
album
.
However
, locating a particular sector
is
a
more
difficult
process.
Two
different
methods
are used
to
locate sectors
on
a disk; hard
sectoring and soft sectoring.
Both
the
hard and soft sector methods
involve
the
use
of
an
index
hole
. The
index
hole
is
shown in
Illustration
5-2.
It
is
located just
to
the
right
of
the
large
hole
in
the
middle
of
the
51/.i
inch
diskette.
The
index
hole
as
shown in Illustration 5-2
is
a
hole
only
in
the
diskette's
protective
covering
.
Another
index
hole
is
located
on
the
actual
diskette
surface inside
the
envelope
.
As
the
diskette
spins,
the
index
hole
(or
holes)
on
the
diskette surface
passes
underneath
the
hole
in
the
protective
envelope.
A
light
source inside
the
disk
drive
shines
light
onto
the
area
of
the
diskette
containing
the
index
hole
.
When
an
index
hole
on
the
disk surface
is
aligned
with
the
index
hole
on
the
protective
envelope
,
the
light
will
shine
through
to
a sensor. The sensor
will
relay
information
on
the
location
of
the
index
holes,
which
can
be used
to
calculate
the
various sector locations.
Now
that
we
have discussed
the
concepts
of
locating
sectors,
we
will
discuss
the
difference
between
hard and soft sectored
diskettes. A hard sectored diskette contains a
number
of
holes,
each
of
which
indicates
the
location
of
a sector.
An
extra
hole
is
used
to
indicate
the
location
of
the
first sector. The
location
of
*The
disk
drive
contains a device
known
as
a
read/write
head,
which
is
used
to
read and
write
information
. The
computer
can
move
the
head
to
any
position
desired
on
the
disk surface.
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