SECTION 9
ERROR DETECTION
AND
CORRECTION
9-1. WRITE ERROR
If an error occurs during a write operation, it
will
be detected on
the
next
revolution by doing a read
operation, commonly called a
"write
check."
To
correct
the error,
another
write and write check
operation
must be done. If
the
write operation
is
not
successful after ten (10)
attempts
have been
made, a read operation should be
attempted
on
another
track
to
determine if the media
or
the
drive
is
failing. If the error still persists, the disk
should be considered defective and discarded.
-
24-
9-2. READ ERROR
Most errors
that
occur will be
"soft"
errors;
that
is,
by
performing an error recovery procedure the
data
will
be recovered.
Soft
errors are usually caused
by:
1. Airborne contaminants
that
pass between the
read/write head and the disk. These contami-
nants will generally be removed by the cartridge
self-cleaning wiper.
2. Random electrical noise
wh
ich usually lasts for
a few
J.l
sec.
3. Small defects
in
the written
data
and/or
track
not
detected during
the
write operation which
may cause a
soft
error during a read.
The
following procedures are recommended
to
recover from the above mentioned soft errors:
1. Reread the track ten
(10) times
or
until such
time as
the
data
is
recovered.
2.
I f
data
is
not
recovered after using step 1, access
the
head
to
the adjacent track
in
the
same direc-
tion
previously moved, then return
to
the
desired
track.
3. Repeat step 1.
4.
If
data
is
not
recovered,
the
error
is
not
recover-
able.
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