Specifications
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SECTION V
MEDIA DEFECTS AND ERRORS
5.1
ERROR MAPPING
AND
QUALIFICATION
In
high density digital recording storage systems, it is necessary to Increase
rellabdlty
and
Improve operational per-
formance.
This
is
done
by
providing
an
error detection
and
correction
scheme.
For
disk
storage systems, the
predominant error pattern
is a burst
of
etlon
occuring
in
one or more
tracks·.
These errors
are
drop-outs (absent
bits). drop-ins (bits added)
1
or
bits shifted from their nominal position
beyond
the
tolerance of the data separator.
, 5.1.1
CauH8
of Errora
The following conditions may result
in
errors:
-
..
'
. .
. .
...
..
.
e·
..
-
..
.
-.
..
a.
Marginal signal
to
noise ratio
of
the read/write circuits.
b.
Marginal characteristics
of
the
me~ia
and
the
read/write
heads.
c. Mispositioning of the
read/write
heads
on
the disk.
d. Defects
or
imperfections in the disk media.
5.1.2
Error
Definition
An
error
is
a discrepancy between
recorded
data and original data.
There
can
be
an
extra
or
missing bit. i.e
..
a ·'0·'
can
be
transformed into a "1"
or
vice versa.
Errors
fall
into two categories: "hard"
or
"soft.·, Hard errors
are
usually the result of
media
defects
and
will
be
repeatable. Soft errors
are
often
caused
by
items
"a"
through.
"c"
of
paragraph
5.1.1.
and
will
normally not
be
repeatable. .
5.1.3
Media
Defect
Definition
Most errors resulting from media defects
are
classified as hard erron. They
are
attributable to small imperfections
in
the
oxide coating of
the
disk, such
as
an
impUrity within the oxide
Itself.
or
a
saatch
on
the
surface of
the
Oxide
coating.
As
the storage size
and
density
of
information lnaeases.
th.M
defects become
more
apparent
to
the system. Win-
chester
technology utilizes a higher bit packing ratio
than
older types
of
drives
and
is
therefore
more
susceptible to
this
type
of
error.
t
5·1