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

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. Air/brass would give very small differences in signal, and we're talking about the times when 7400 TTL logic with 4 gates per package was state of the art, so big signals were good.

"Although the wombat is real and the dragon is not, few know what a
wombat looks like, but everyone knows what a dragon looks like."

        -- Avram Davidson, _Adventures in Unhistory_
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