Wang 2200 - Page 9

In a standard
configuration
(see
Figure
2-1)
,
one Model 2280 disk drive
is
connected
to
the DPU. The DPU is
attached to the 2200 Series Central
Processing Unit (CPU)
via
a
standard Model 22C03
disk controller.
In
a
dual
system
configuration
(see
Figure
2-2)
, a
2280N disk drive is
cabled to
the
2280
disk drive,
and its output
lead is connected
to
the DPU. Both disk units
may thereby be
controlled by the
same DPU.
The
Model
2280/2280N Disk
Drives
contain up to
four disk platters
mounted horizontally
on
a
single drive shaft. The platters are mounted one
above
the other,
somewhat as
phonograph records are stacked on
a
record
changer (see
Figure
1-2)
. The top
disk platter is housed in
a
cartridge which
can
be
removed
from the
disk
unit
and replaced; it is therefore referred to as
the
removable
disk
platter. Because it is
contained in
a
sealed,
cartridge-like
casing to
protect it
from damage when it is removed from
the
disk unit,
the
removable platter
is also sometimes referred
to as a
disk
cartridge.
The
other three disk
platters
are
positioned below the removable
platter
on the
shaft. As an
integral part of the
disk
unit, they cannot
be
removed,
suid are
therefore called the
fixed disk platters. The
shaft itself
is coupled to
a
drive
motor
which spins the disk platters
at a
constant
speed
of 3600
rpm.
Information is
recorded on, or read from, the surface of a disk platter
via
the
read/write head. The
read/write heads are attached
to a
comb-type
access
assembly consisting
of four access arms
(see
Figure
1-3)
.
The
read/write head is
fixed in position
and cannot move independently
of the
access
arm.
When
a
disk
statement or commamd is executed
from
the system CPU, the
access
assembly
moves the read/write
heads in and
out
over the surface of
the
disk
platters as they
rotate. A
read/write head CcUi then record
(write)
information
on
a
surface
of
a
disk platter
or retrieve (read) information
from
a platter as
the
platter rotates past the head's
position.
The
fixed platters
can contain up to five
recording
surfaces with one
track
servo
surface; the removable
platter contains one surface which is
a
recording
surface and
one which is
a
track
servo surface. A servo surface
contains
prerecorded
information that
is
used
by the drive electronics
to
position the
read/write heads to
the desired track. (The number of recording
surfaces
accessible
in each
Model 2280/2280N disk unit is shown in the
following table.)