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IBM 2841 Storage Control and 2311 Disk Storage Drive
The
IBM
2841 Storage Con
trol provides
attachment and
control facilities for connecting
IBM
2311
Disk Storage
Drives
to the
1800
system.
A
single 2841
provides
for
attachment of
up
to eight 2311,
Modell,
Disk
Storage
Drives.
2841 Storage Control
The
2841 is con nected to the
1800
system
via
a selector
channel which in turn operates
under data
channel con-
trol.
The
2841 interprets and executes commands,
pro-
vides a data path between the selector channel and 2311 's,
translates data, and furnishes status information to
the
selector channel.
A two-channel switch special feature for the 2841
allows the 2841 to be shared by two separate channels and
also allows individual
devices to be
reserved for exclusive
use of either channel.
The
two channels
may be
selector
channels from separate 1800 systems or a selector channel
from an 1800 system and a channel from
System/360.
Channel switching and
device reservation in
the 2841 are
performed under
control of
the
stored
program.
2311 Disk Storage Drive
The
2311 is a random access storage
device
that functions
as
both
an input and output device
.
The
storage medium
is
the
IBM 1316 Disk Pack
(Figure 26). Each
disk pack
consists of
six 14-inch disks
,
mounted
a
half-inch
apart on a central
hub. Data is re-
corded on the inside ten
disk
surfaces.
The two
outer
surfaces are covered
by
protective
plates
and serve as
pro-
tectors for the
inside disk
surfaces.
The
entire
pack
of
Figure 26. 1316
Disk Pack
disks is
covered
by
a two-piece
plastic cover.
Information
is
written on and
read from
the ten disk
surfaces
as
they
revolve (at
2,400 rpm) past ten read/write
heads. The read/write heads
are
mounted in pairs,
between
each two disks,
on a
movable
comb-like access
mechanism.
An
actuator
moves
the access mechanism
horizontally
allowing
the
read/write heads to
have
access
to the
entire
recording surface on each of the
ten disk
surfaces.
As
the access
mechanism
is moved horizontally,
it may
be stopped
at any of 203
positions. This provides
203 data
tracks
on each surface. Since all ten
rt~J/wnte
heads
are
moved by
a single access
mechanism
,
a cylinder
of ten
data
tracks is
available at each access mechanism
position.
OPERATOR CONTROLS, 2841
(Figure
27)
The
Enable/Disable
Switch
enables or
disabl
es communi-
cation
between
the 2841 and the
1800
system.
It
also
enables or
disables the
2841
usage meter.
If the 2841
has
the two-channel switch feature
,
a separ-
ate switch is
provided
for each chann el
;
however
,
there
is
still only one usage
meter. Providing
t
wo
switches allows
each channel to
be disabled independently. While in the
disabled
state
,
the 2841 will
not be
selected
by
that chan-
nel.
In
order to
disable
a channel,
the
following conditions
70
IBM 1800 Operating Procedures
must
exist
:
1.
The
enable/disabl
e switch
for
that channel
must
be
in the disabled position.
2.
The
channel selection switch
in the
2841
must not
be
selected
to
the
disabled
channel
(two-channel switch
feature only.)
3.
The
processor-controller must
be
in the stopped or
wait
state.
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