On Thu, 21 Oct 2010 14:32:23 +0100
Arthur Chance <free...@qeng-ho.org> wrote:

> On 10/21/10 13:38, RW wrote:
> > On Wed, 20 Oct 2010 21:10:28 +0100
> > Arthur Chance<free...@qeng-ho.org>  wrote:
> >
> >
> >> 50s) had the experience of programming microcode on a machine by
> >> inserting brass slugs for 0s and ferrite slugs for 1s on a pin
> >> board.
> >
> > I wonder why it was brass/ferrite rather than brass/empty or
> > ferrite/empty.
> Dredging up physics unused for 30+ years, ferrite is ferromagnetic
> and intensifies magnetic fields so a coil of wire with ferrite inside
> is a massively bigger inductor then an empty coil. I vaguely remember
> that brass is slightly diamagnetic, but could be mistaken. If it is,
> then it would have the opposite effect and reduce the inductance, so
> you'd get a better difference in signal between brass/ferrite than
> air/ferrite. 

Possibly. I'm wondering if there might be three states, where the third
state is writable.

> Air/brass would give very small differences in signal,

I was thinking in that case it would be open/short circuit.
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