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PRESENTED BY-

SUKUMAR SARKAR (CSM 11057)

PAWAN GUPTA (CSM 11006)

AMIT DUBEY (CSM 11020)

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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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A 32 x 32 core memory plane storing 1024 bits of data

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INTERNAL STRUCTURE

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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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And it retain its magnetism even when the external magnetising field has been removed.

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Why Ferrite?Because ferrite can be easily magnetised and demagnetised by the passage electriccurrent.

Some key conceptsMagnetic 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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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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Large current downward Strong clockwise field

Large current upward Strong anti-clock wise field

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Produces Negative flux ,,Which results in the storage ofZERO in the Ferrite Core

Produces Positive flux ,,Which results in the storage ofONE in the Ferrite Core

Magnetic HysteresisIt is a closed curve which shows the variation

of the magnetic flux density and external magnetic field.

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Magetic hysteresis of a ferrite core

Magnetic hysteresis of amaterial

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Organisation of Magnetic-coreMemory unit containing 4-words with three bits each.

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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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.

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Write operationDuring 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.

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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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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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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 timeThe 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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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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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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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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