3. Magnetic core memory, or ferrite-core
memory, is an early form of random access
computer memory. It uses small magnetic
ceramic rings, the cores, through which wires
are threaded to store information via the
polarity of the magnetic field they contain.
Such memory is often just called core memory,
or, informally, core.
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4. A 32 x 32 core memory plane storing 1024 bits of data
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6. What is Ferrite??
Ferrite is a ceramic material formed by reacting metal
oxides into a magnetic material.(It is a compound of
ferromagnetic metal,e.g,Iron)
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7. Why Ferrite?
Because ferrite can be easily magnetised
and demagnetised by the passage electric
current.
And it retain its magnetism even when the external
magnetising field has been removed.
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8. Some key concepts
Magnetic Field
A region around a magnetic material(Here Ferrite) or a
moving electric charge within which the force magnetism
acts.
Magnetisation
The process of making a substance temporarily or
permanently magnetic , as by insertion in a magnetic field.
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9. Magnetic Flux
The number of lines of force passing through a given area is
defined as Magnetic Flux.
The magnetic field of a current-carrying wire
current in a wire creates a magnetic field circulating about
the wire, whose strength is proportional to the size of the
current. If we reverse the direction of the current, the
magnetic field circulates in the opposite direction:
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10. Large current downward
Strong clockwise field
Produces Negative flux ,,
Which results in the storage of
ZERO in the Ferrite Core
Large current upward
Strong anti-clock wise field
Produces Positive flux ,,
Which results in the storage of
ONE in the Ferrite Core
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11. Magnetic Hysteresis
It is a closed curve which shows the variation of the
magnetic flux density and external magnetic field.
Magnetic hysteresis of a Magetic hysteresis of a
material ferrite core 11
13. DR(Driver)
Generates current pulses to magnetise the cores in the
two magnetising states as mentioned earlier.
SA(Sense Amplifier)
It amplifies detects the pulses induced in the sense
wire winding when the magnetic memory core
switches its states .
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14. Read and Write Operation
Read operation
The word driver current pulse is applied to the cores of
the word selected by the decoder.
The read current is in negative direction causing all
cores of the selected word to go to the 0 state.
The cores which were in one state ,switch their flux
which induce a voltage into sense wire . The voltage
pulse on the sense wire of cores with a previous is
amplified in the sense amplifier and sets the
corresponding flip-flop in the buffer register.
The delay in sensing the voltage pulse is called the
access time of the core memory. 14
15. Write operation
During a write operation , the buffer
register holds the information to be stored
in the word specified by the address
register.
A current pulse is generated
simultaneously in the word driver selected
by the decoder and in the bit driver, whose
corresponding buffer register flip-flop
contains a 1(one).
Both currents are in the positive direction ,
but their magnitude is only half that is
needed to switch the flux to the 1 state. 15
16. A core switches to the 1 state only if there is a
coincidence of two half currents from a word driver
and bit driver. The result is that the magnetisation of
cores is switched to the 1 state only if the word and
bit wires intersect , i,e; only in the selected word and
only in the bit position in which the buffer register
is a 1(one).
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17. Problems while reading and writing
Reading of an information stored in the selected
word is destroyed by the reading process.
Since it turns all cores to its zero state.
And the write operation works properly only if the
cores are initially cleared.
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18. RESTORE OPERATION:
The restore operation during a read cycle is equivalent to a
write operation which ,in effect , writes the previously read
information from the buffer register back into the word
selected .
The access time plus the time to rewrite is the memory
cycle time
The clear operation during a write cycle is equivalent to a
read operation which destroys the stored information but
prevents the read information from reaching the buffer
register by inhibiting the sense amplifier.
Restore and clear cycles are normally initiated by the
memory internal control .
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19. ADVANTAGES OF MAGNETIC /FERRITE
CORE MEMORY
It was more cost effective than high performance vacuum
tube or transistor memory and provided better
performance than low cost drum memory.
It is volatile in nature.
The components had a higher life time expectancy and
their operating characteristics do not alter over time
The Magnetic core needs no power to retain its data.
Magnetic core memory is permanently magnetised either
in clockwise or anti-clockwise direction.
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20. DISADVANTAGES
(1) Magnetic core memory has been replaced by
semiconductor memory because each integrated
circuit in semiconductor memory contains
thousands of semiconductor devices which
represents million of bit.
(2) Magnetic core memory don’t get smaller than
that required by simple calculator.
(3) Reading a bit from a core sets its state to zero
which is a term of destructive reading which
needs a write cycle to restore the previous bit.
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21. USES OF MAGNETIC /FERRITE CORE
MEMORY
It is uses as a secondary storage device due to its non
volatility.
Magnetic core memory is used as a computer memory
as their behaviour when external magnetic field is
applied.
It can be used as storage device.
Magnetic core memory is used to capture the
imaginations of modern enthusiast.
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