Core Memory

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Core Memory

• Core memory consist of ferrite cores.
• Core memory is a form of non-volatile memory.
• Used 1950 .. 2000

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Core Memory Construction
The "Donuts" are made of Ferrite, a material that
can hold a magnetic field in either of two
directions, thus representing "1" or "0". The
wires through the cores allow the computer to set
or read the magnetic direction. or
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A Core Stack
A Core Stack containing 500 bytes
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65536 bits(!) of core memory
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Bit by bit
Each ring stores one bit (a 0 or 1). One bit in
each plane could be accessed in one cycle, so
each machine word in an array of words was spread
over a stack of planes. Each plane would
manipulate one bit of a word in parallel,
allowing the full word to be read or written in
one cycle.
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Construction
Core relies on the hysteresis of the magnetic
material used to make the rings. Only a magnetic
field over a certain intensity (generated by the
wires through the core) can cause the core to
change its magnetic polarity. To select a memory
location, one of the X and one of the Y lines are
driven with half the current required to cause
this change. Only the combined magnetic field
generated where the X and Y lines cross is
sufficient to change the state, other cores will
see only half the needed field, or none at all.
By driving the current through the wires in a
particular direction, the resulting induced field
forces the selected core's magnetic field to
point in one direction or the other (north or
south).
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Configuration
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Destructive Read-out
A read operation on a core memory bit is always
destructive, so the read operation must always be
followed by a write operation. Cycle times for
core memory were around 1 microsecond. This is
comparable to processor cycle time in those days.
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Non-volatile
Core memory is non-volatile storage it can
retain its contents indefinitely without power.
It is also relatively unaffected by EMP and
radiation. These were important advantages for
some applications like military installations and
vehicles like fighter aircraft, as well as
spacecraft, and led to core being used for a
number of years after availability of
semiconductor MOS memory. For example, the Space
Shuttle flight computers initially used core
memory, which preserved the contents of memory .
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On display
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The future(?) M-RAM - 1

• Magnetoresistive Random Access Memory (MRAM) is a
  non-volatile computer memory (NVRAM) technology,
  which has been under development since the 1990s.
  Continued increases in density of existing memory
  technologies, notably Flash RAM and DRAM kept
  MRAM in a niche role in the market, but its
  proponents believe that the advantages are so
  overwhelming that MRAM will eventually become
  dominant.

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The future(?) M-RAM - 2

• Unlike conventional RAM chip technologies, in
  MRAM data is not stored as electric charge or
  current flows, but by magnetic storage elements.
  The elements are formed from two ferromagnetic
  plates, each of which can hold a magnetic field,
  separated by a thin insulating layer. One of the
  two plates is a permanent magnet set to a
  particular polarity, the other's field will
  change to match that of an external field. A
  memory device is built from a grid of such
  "cells".

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Documentation License, Version 1.2
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The future(?) M-RAM - 3
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Documentation License, Version 1.2