Re: Core memory

[Steve VanDevender <stevev@efn.org>]

Timothy van der Linden writes:
 > > > Why doesn't the magnetic field in the ferrite core degrade? (I assume the
 > > > ferrite has some resistance.)
 > >
 > >Have you ever known other magnets to degrade?  Once magnetized, a
 > >material won't demagnetize unless exposed to heat above its Curie point
 > >or another sufficiently strong magnetic field.
 > 
 > Oh, now I understand, you create a permanent magnetic field just like
 > magnetic discs and tapes. (I though you created a current in the core) So in
 > fact the cores don't need to be closed completely.
 > 
 > Tim

The core is in essence just a lump of magnetizable material; they were
generally made toroidal because it was easiest to string them that way.

There were some designs for magnetic memory that didn't use cores, but
(if I recall correctly) used spots of magnetic material sandwiched
between two layers of parallel conductors.  And even more exotic memory
hardware has existed -- ever heard of mecury delay lines?  Williams
tubes?