Greybeards (Re: Netbooks & BSD)

[Arthur Chance]

On 10/21/10 13:38, RW wrote:
> On Wed, 20 Oct 2010 21:10:28 +0100
> Arthur Chance<freebsd at 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. 
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_