<s>
A	O
disk	B-Device
read-and-write	I-Device
head	I-Device
is	O
the	O
small	O
part	O
of	O
a	O
disk	B-Device
drive	I-Device
which	O
moves	O
above	O
the	O
disk	B-Device
platter	O
and	O
transforms	O
the	O
platter	O
's	O
magnetic	O
field	O
into	O
electrical	O
current	O
(	O
reads	O
the	O
disk	B-Device
)	O
or	O
,	O
vice	O
versa	O
,	O
transforms	O
electrical	O
current	O
into	O
magnetic	O
field	O
(	O
writes	O
the	O
disk	B-Device
)	O
.	O
</s>
<s>
In	O
a	O
hard	O
drive	O
,	O
the	O
heads	O
fly	O
above	O
the	O
disk	B-Device
surface	O
with	O
clearance	O
of	O
as	O
little	O
as	O
3	O
nanometres	O
.	O
</s>
<s>
The	O
flying	B-Device
height	I-Device
has	O
been	O
decreasing	O
with	O
each	O
new	O
generation	O
of	O
technology	O
to	O
enable	O
higher	O
areal	B-Device
density	I-Device
.	O
</s>
<s>
The	O
flying	B-Device
height	I-Device
of	O
the	O
head	O
is	O
controlled	O
by	O
the	O
design	O
of	O
an	O
air	O
bearing	O
etched	O
onto	O
the	O
disk-facing	O
surface	O
of	O
the	O
slider	O
.	O
</s>
<s>
The	O
role	O
of	O
the	O
air	O
bearing	O
is	O
to	O
maintain	O
the	O
flying	B-Device
height	I-Device
constant	O
as	O
the	O
head	O
moves	O
over	O
the	O
surface	O
of	O
the	O
disk	B-Device
.	O
</s>
<s>
If	O
the	O
head	O
hits	O
the	O
disk	B-Device
's	O
surface	O
,	O
a	O
catastrophic	O
head	O
crash	O
can	O
result	O
.	O
</s>
<s>
The	O
gap	O
determines	O
the	O
minimum	O
size	O
of	O
a	O
recorded	O
area	O
on	O
the	O
disk	B-Device
.	O
</s>
<s>
Metal-in-gap	O
(	O
MIG	O
)	O
heads	O
are	O
ferrite	O
heads	O
with	O
a	O
small	O
piece	O
of	O
metal	O
in	O
the	O
head	B-Device
gap	I-Device
that	O
concentrates	O
the	O
field	O
.	O
</s>
<s>
First	O
introduced	O
in	O
1979	O
on	O
the	O
IBM	B-Device
3370	I-Device
disk	B-Device
drive	I-Device
,	O
thin-film	O
technology	O
use	O
photolithographic	B-Algorithm
techniques	O
similar	O
to	O
those	O
used	O
on	O
semiconductor	O
devices	O
to	O
fabricate	O
HDD	B-Device
heads	I-Device
with	O
smaller	O
size	O
and	O
greater	O
precision	O
than	O
the	O
ferrite-based	O
designs	O
then	O
in	O
use	O
.	O
</s>
<s>
Thin	O
layers	O
of	O
magnetic	O
(	O
Ni	O
–	O
Fe	O
)	O
,	O
insulating	O
,	O
and	O
copper	O
coil	O
wiring	O
materials	O
are	O
built	O
on	O
ceramic	O
substrates	O
that	O
are	O
then	O
physically	O
separated	O
into	O
individual	O
read/write	B-Device
heads	I-Device
integrated	O
with	O
their	O
air	O
bearing	O
significantly	O
reducing	O
the	O
manufacturing	O
cost	O
per	O
unit	O
.	O
</s>
<s>
The	O
geometry	O
of	O
the	O
head	B-Device
gap	I-Device
was	O
a	O
compromise	O
between	O
what	O
worked	O
best	O
for	O
reading	O
and	O
what	O
worked	O
best	O
for	O
writing	O
.	O
</s>
<s>
The	O
term	O
AMR	O
(	O
Anisotropic	O
MR	O
)	O
is	O
used	O
to	O
distinguish	O
it	O
from	O
the	O
later	O
introduced	O
improvement	O
in	O
MR	O
technology	O
called	O
GMR	B-General_Concept
(	O
giant	B-General_Concept
magnetoresistance	I-General_Concept
)	O
and	O
"	O
TMR	O
"	O
(	O
tunneling	O
magnetoresistance	O
)	O
.	O
</s>
<s>
The	O
transition	O
to	O
perpendicular	B-Device
magnetic	I-Device
recording	I-Device
(	O
PMR	O
)	O
media	O
has	O
major	O
implications	O
for	O
the	O
write	O
process	O
and	O
the	O
write	O
element	O
of	O
the	O
head	O
structure	O
but	O
less	O
so	O
for	O
the	O
MR	O
read	O
sensor	O
of	O
the	O
head	O
structure	O
.	O
</s>
<s>
The	O
introduction	O
of	O
the	O
AMR	O
head	O
in	O
1990	O
by	O
IBM	O
led	O
to	O
a	O
period	O
of	O
rapid	O
areal	B-Device
density	I-Device
increases	O
of	O
about	O
100%	O
per	O
year	O
.	O
</s>
<s>
In	O
1997	O
GMR	B-General_Concept
,	O
giant	B-General_Concept
magnetoresistive	I-General_Concept
heads	O
started	O
to	O
replace	O
AMR	O
heads	O
.	O
</s>
<s>
In	O
2004	O
,	O
the	O
first	O
drives	O
to	O
use	O
tunneling	O
MR	O
(	O
TMR	O
)	O
heads	O
were	O
introduced	O
by	O
Seagate	O
allowing	O
400	O
GB	O
drives	O
with	O
3	O
disk	B-Device
platters	O
.	O
</s>
<s>
Seagate	O
introduced	O
TMR	O
heads	O
featuring	O
integrated	O
microscopic	O
heater	O
coils	O
to	O
control	O
the	O
shape	O
of	O
the	O
transducer	B-Algorithm
region	O
of	O
the	O
head	O
during	O
operation	O
.	O
</s>
<s>
The	O
heater	O
can	O
be	O
activated	O
prior	O
to	O
the	O
start	O
of	O
a	O
write	O
operation	O
to	O
ensure	O
proximity	O
of	O
the	O
write	O
pole	O
to	O
the	O
disk/medium	O
.	O
</s>
<s>
This	O
improves	O
the	O
written	O
magnetic	O
transitions	O
by	O
ensuring	O
that	O
the	O
head	O
's	O
write	O
field	O
fully	O
saturates	O
the	O
magnetic	O
disk	B-Device
medium	O
.	O
</s>
<s>
The	O
same	O
thermal	O
actuation	O
approach	O
can	O
be	O
used	O
to	O
temporarily	O
decrease	O
the	O
separation	O
between	O
the	O
disk	B-Device
medium	O
and	O
the	O
read	O
sensor	O
during	O
the	O
readback	O
process	O
,	O
thus	O
improving	O
signal	O
strength	O
and	O
resolution	O
.	O
</s>
