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FDD412A/B
(a)
In most
magnetic
recording
implementations,
writing
new
data
automatically
erases
old
data.
The
erase
head
is not
specifically
needed.
(b)
But
the
floppy
disk
is often
subjected
to
read/write
opera-
tions
as
it
is
exchanged
between
FDDs.
(c)
Assume
that
there
is no
erase
head
and
that
data
is
recorded
as
shown
in Fig.
2.16
(A).
(ad)
The
disk
is
then
subjected
to writing
on
another
FDD.
At
this
time,
the
head
is
a bit
out
of position,
and
the writing
is
done
as
shown
in Fig.
2.16
(B).
(e)
When
data
of
(B)
is read by the magnetic
head
shown
in
Fig.
2.16
(C),
the
old
data
(remaining
data)
shaded
in
(C)
and
new
data
are
read
in
together.
The
old
data
causes
noise,
resulting
in read
error.
(£)
To provide
for head
displacement
on
different.FDDs,
both
sides
are
erased
by an
erase
head
for
removal
of old
data,
as
shown
in Fig.
2.16
(D).
In this
way,
the
tracks
always
contain
the
latest
data
and
can
prevent
noise
due
to
remaining
data.
Remaining
data
(A)
Write
(B)
Rewrite
(C)
Read
Erased
Recorded
data
(D)
Tunnel
erase
Fig.
2.16
Tunnel
Erase System
2.5.4
Data
Write
Operation
(1)
Interface
signals
Table
2.11
Data Write
Interface
Signals
Signal
Name
Function
WRITE
GATE-N
a
Instructs
a write
operation.
The
FDD
has
a current
flow
in
the
heads
while
this
signal
is on.
RITE
DATA-N
Data
for
recording
on
medium;
infor-
mation
modulated
by FM/MFM
method.
LOW
CURRENT-N
Switches
write
current
levels
between
outer
and
inner
tracks.
eae
Tracks
0143
(large
current):
'H'
level
Tracks
44.76
(small
current):
'L'
level
AD
1 SELECT-N|
Selects
the
head.
Head
0:
'H'
level
Head
1:
'L'
level
—20-
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