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BUBBLE MEMORYMAGNETIC CORE

NVRAM

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MEMORY

• In computing, memory refers to the computer hardware devices used to store information for immediate use in a computer.

• Volatile memory Eg. DRAM, SRAM.• Non-volatile memory Eg. Bubble memory, magnetic core memory

and NVRAM.

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Magnetic Bubble Memory Description • Magnetic bubble memory technology was introduced by Bell

Telephone Laboratories in 1967.

• Small cylindrical magnetic domains, which are called magnetic bubbles

• The presence or absence of a bubble in a bit position is used to define the logic state.

• Since the diameter of a bubble is so small (as little as a tenth of a micrometer), many thousands of data bits can be stored in a signle bubble-memory chip.

• In the spring of 1977 Texas Instruments was the first to market a 92,304-bit (11.25kb approx) bubble memory.

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Ferromagnetism vs. orthomagnetism

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The orthomagnetic sheet in bubble memory

-orthomagnetic axis os perpendicular to the square surface

-uniaxial magnetic property

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Squeezing the bubbles down in size

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Moving the bubbles using external magnetic fields

PUSHPULL

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Driving coils and guide patterns

steady rotating magnetic field

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Different guidance patterns

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Bubbles moving in the T-I-style pattern

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Bubbles moving in the V-style pattern

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• It is conceptually a stationary disk with spinning bits.

• In order to read or write the bubbles, they are rotated past the equivalent of a read/write head.

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ADVANTAGES

• Data is retained even when power is no longer applied to the chip.

• Solid-state technology ( no moving parts)– they have higher reliability than tape or disc storage – no preventive maintenance.

• Small and lightweight

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MAGNETIC CORE MEMORY

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What is magnetic core memory?

• Magnetic 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.

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How core memory works?

READING

•To read a bit of core memory, the circuitry tries to flip the bit to the polarity assigned to the 0 state, by driving the selected X and Y lines that intersect at that core.

•If the bit was already 0, the physical state of the core is unaffected.

•If the bit was previously 1, then the core changes magnetic polarity. This change, after a delay, induces a voltage pulse into the Sense line.

•The detection of such a pulse means that the bit had most recently contained a 1. Absence of the pulse means that the bit had contained a 0. The delay in sensing the voltage pulse is called the access time of the core memory.

•Following any such read, the bit contains a 0. This illustrates why a core memory access is called a destructive read: Any operation that reads the contents of a core erases those contents, and they must immediately be recreated.

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Writing

• To write a bit of core memory, the circuitry assumes there has been a read operation and the bit is in the 0 state.

• To write a 1 bit, the selected X and Y lines are driven, with current in the opposite direction as for the read operation. As with the read, the core at the intersection of the X and Y lines changes magnetic polarity.

• To write a 0 bit (in other words, to inhibit the writing of a 1 bit), the same amount of current is also sent through the Inhibit line. This reduces the net current flowing through the respective core to half the select current, inhibiting change of polarity.

• The access time plus the time to rewrite is the memory cycle time.

• The Sense wire is used only during the read, and the Inhibit wire is used only during the write. For this reason, later core systems combined the two into a single wire, and used circuitry in the memory controller to switch the function of the wire.

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Advantages:

• It was more cost effective than high performance vacuum tube or transistor memory.

• Better performance than low cost drum memory.

• It is non-volatile in nature.

• The components had a higher life time expectancy and their operating characteristics do not alter over time.

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Disadvantages

• Magnetic core memory has been replaced by semiconductor memory because each integrated circuit in semiconductor memory contains thousands of semiconductor devices which represents millions of bit.

• Magnetic core memory don’t get smaller than that required by simple calculator.

• 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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NVRAM

• Non-volatile random-access memory (NVRAM) is random-access memory that retains its information when power is turned off.

• The NVRAM is a small 24 pin DIP (Dual Inline Package) integrated circuit chip and is thus able to obtain the power needed to keep it running from the battery installed in your motherboard.

• NVRAM is also in your computer monitor, printers, cars, smart cards, and other devices that require remembered settings

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Types of NVRAM• SRAM (Static Random Access

Memory): It is made non-volatile by connecting it to a constant power source such as a battery. Since SRAM requires continual power supply in order to maintain its data, an NVRAM that is made from an SRAM will need to use an available power supply to make sure it continues working.

• Ferroelectric RAM, FeRAM or F-RAM and Magneto resistive RAM or MRAM are also types of NVRAM used for various applications.

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Advantages of NVRAM

• Provides excellent performance when compared to other non-volatile memory products

• Supports applications that need quick read or write operations using non-volatile memories, such as antilock braking systems and parallel processing controllers for local area networks.

• Less power is required for NVRAMs, so the backup guarantee can be ensured for up to 10 years.

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Disadvantage of NVRAM

• If the battery embedded in the NVRAM chip fails, then this means that your system clock will stop running and important system configuration information may not be maintained.

• Lower storage density• Overall capacity limitation• Higher cost

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THANK YOU!

SPECIAL MENTION,PROF. KASHYAP JOSHI