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Thirteen-Digit Addressing
•
Thirteen binary digits address 8,192
storage locations.
•
Address range 0000000000000 to
1111111111111 (0000-8191 decimal).
In the first example of addressing
(Figure 2-36), selection depended on one
group of binary digits.
This was
expanded to selection by three groups of
binary digits (Figure 2-38).
If a
fourth group is added to provide a
fUrther means of selection, the total
amount of addressable storage can be
increased.
With an additional three binary
digits to provide eight more combina-
tions of numbers, the
tot~l
amount of
addressable storage is increased by a
factor of eight from 1,024 to 8,192
(Figure 2-39).
These additional three
binary digits provide a fourth direction
to the addressing.
Basic addressing is
the same as shown in Figure 2-38 except
that now there are eight groups of 1,024
storage locations.
The three additional
digits determine which of the eight
groups of 1,024 is to
he
used.
Notice
that address selection depends on the
coincidence of lines from four direc-
tions.
Up to this point, reference has been
made only to storage locations, with no
attempt made to describe the actual
storage device.
In the examples given,
the storage locations could have been in
any storage device, depending on what
was to be stored.
In the IBM 2030 Proc-
essing Unit, a storage device is needed
to store information, program instruc-
tions, constants, and data for process-
ing.
The storage device must be capable
of storing and/or supplying the required
information in the range of several
microseCOnds.
Thus the multiplicity of
switches and boxes used to demonstrate
storage addressing in FIgure 2-39 are
~not
satisfactory.
However, it is possi-
ble to apply the same addressing scheme
to faster storage devices.
An investi-
gation into the properties of magnetic
core storage reveals that this device
can be readily applied to produce an
extremely fast storage device capable of
storing the information required in the
IBM 2030 Processing Unit.
2-28
The basic core storage size is 8,192
positions.
Using the 13-digit address-
ing scheme described, a unique binary
address can be assigned to each of the
8,192 positions.
MAGNETIC CORE THEORY
•
A magnetic core is a small,
doughnut-shaped object.
•
•
•
Made of ferromagnetic material.
Can be magnetized to either of two
pola.rities.
Once magnetized, the core retains
its magnetism until it is deli-
berately changed by an external
magnetizing force.
•
External magnetizing force created
by current-carrying wires.
A magnetic core is a tiny, doughnut-
shaped object made of a ferromagnetic
material.
The properties of this
material are such that if a ferromagnet-
ic core is introduced to a sufficiently
strong magnetic field, the core becomes
magnetized.
Furthermore, if the core is
removed from the vicinity of the magnet-
ic field, it remains magnetized.
Unless
it is delibe.rately changed, the core
retains its magnetism indefinitely.
To deliberately change the core, it
must be introduced to a sufficiently
strong magnetic field of the opposite
polarity.
This causes the core to be
magnetized in the opposite direction.
Once again, unless deliberately changed,
the core retains its magnetism indefin-
itely.
The fact that the core may be set to
either of two states makes it a very
useful binary storage device.
If, when
the core is magnetized in one direction
a binary value of 1 is assigned, then a
binary value of 0 results when the core
is magnetized in the opposite direction.
Moving the core to the vicinity of a
magnetic field is not a practical method
of storing binary information.
A more
suitable method is to have a controlla-
ble magnetic field near the core itself.
To magnetize the core in either of two
directions, this magnetic field must be
reversible in polarity.
The desired
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