2.2.8
TYPE
OF
HEADS
2.2.8.1
READ/WRITE
HEAD
The
read/write heads
used
in the
BASF
6106/6108
disk drives are tunnel erase type heads.
Data
is
recorded at a flux
density
of
3536
to
5536
flux changes per inch
(fei).
The
nominal
frequencies
on
the read/write
head
are 62.5
kHz
and
125
kHz
when
FM
recording
technique
and
62.5
kHz,
125
kHz
and
83.3
kHz
when
MFM
recording technique
is
used.
In
FM
mode
the
nominal
distance
between
flux
reversals
is
4
JUS
or 8 jUs.
In
MFM
6
JUS
flux revers al
spacings are also encountered.
The
radial
density
is
48
tracks
per inch
(tpi).
This gives 0.0208 inch
nominal
track
to
track
spacing.
The
tunnel erase
gaps
trim the track
width
from
0.014 inch
after
write
to
0.013 inch
after
erase (see Fig. 2-27).
;;~~;;~:~~~::,J;.;;~lll~
-
---.-,--
~O
. 8
mil
7
.8
mi
1
1
~EI;~I~~~~\~~:~:lillt
13
:
mil
WRITTEN
DATA
TUN~EL
ERASED
DATA
FIG.
2 -
27
TRACK
GEOMETRY
The
read/write
head
contains three
coils:
two
read/write
coils
and
the erase
coil
(see Fig. 2-28).
The
erase
coil
is
energized during every write
operation
and
limits
the track width
and
provides
low
noise guard
bands
on
each side of the recorded
track.
The
two
read/write
coils
are
wound
on
a
single
core
and
are center tapped.
The
electrical
connections of the read/write
head
are
shown
in
Fig. 2-28.
During
a write operation the write current
will
be
directed
alternately
to
one
of the
two
readl
write
coils
by
a
flipflop.
This causes a flux
change
every
bit
to
be
written.
The
old data
on
the track
will
be
overwritten
by
the
new
data stream.
On
a read operation
an
output voltage
is
induced
in the readjwrite
head
by
every flux change
that
passes the
gap
of the readjwrite head. This voltage
is
used
by
the read
circuits
to
recover the
written
data.
INPUT
FROH
WRITE
DRIVER
OR
OUTPUT
TO
!lEAD AMPLIFIERS
HEAD
SELECT
SWITCH
R/W-
COILS
CENTER
TAP
_ERASE
COIL
,7
FIG.
2 -
28
ELECTRICAL
CONNECTION
OF
THE
READj
WRITE
HEAD
2 -
20
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