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IBM System/370 Guide

IBM System/370
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Access
Access mechanism
per track
Access mechanism
64 recording tracks/surface x 12
=
768
recording tracks/module
8 spare tracks/surface x 12 = 96 spare tracks/module
8 recording elements
1 spare
8 recording
elements
1 spare
216 recording
elements (read/write headsl/access mechanism x 4 =
864
recording elements
Figure
20.15.1.
Top
view
of
a
2305
Model
2
disk
surface
DATA
RECORDING
ON
THE
MODEL
1
Access
mechanism
Self-formatting
records
are
written
on
a
Modell
as
on
a
Model
2.
However,
data
is
recorded
on
the
disks
of
a
Modell
module
in
a
unique
way
in
order
to
achieve
faster
data
access.
The
Modell
module
contains
the
same
number
of
recording
elements
as
the
Model
2,
but
they
are
positioned
in
such
a
way
as
to
double
the
data
transfer
rate
and
halve
the
average
access
time.
The
capacity
of
the
Model
1
is
less
than
half
that
of
the
Model
2
because
(1)
only
384
recording
tracks
and
48
spare
tracks
are
used,
(2)
there
are
two
RO
records
present
on
each
physical
track
(360-degree
arc)
of
the
Modell,
and
(3)
the
gaps
between
data
areas
on
a
Model
1
track
are
larger
than
those
of
the
Model
2
because
of
the
higher
data
rate
of
the
Modell.
An
addressable
recording
track
on
a
Model
1
occupies
a
180-degree
arc
on
a
disk
surface
rather
than
a
360-degree
arc
as
on
a
Model
2.
43

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IBM System/370 Specifications

General IconGeneral
BrandIBM
ModelSystem/370
CategoryServer
LanguageEnglish

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