From owner-freebsd-questions@FreeBSD.ORG Thu Oct 21 13:32:25 2010 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 657D3106566C for ; Thu, 21 Oct 2010 13:32:25 +0000 (UTC) (envelope-from freebsd@qeng-ho.org) Received: from blue.qeng-ho.org (blue.qeng-ho.org [217.155.128.241]) by mx1.freebsd.org (Postfix) with ESMTP id E45688FC22 for ; Thu, 21 Oct 2010 13:32:24 +0000 (UTC) Received: from fileserver.home.qeng-ho.org (localhost [127.0.0.1]) by fileserver.home.qeng-ho.org (8.14.4/8.14.4) with ESMTP id o9LDWNVV064664; Thu, 21 Oct 2010 14:32:23 +0100 (BST) (envelope-from freebsd@qeng-ho.org) Message-ID: <4CC040E7.7090404@qeng-ho.org> Date: Thu, 21 Oct 2010 14:32:23 +0100 From: Arthur Chance User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.1.12) Gecko/20101007 Thunderbird/3.0.8 MIME-Version: 1.0 To: RW References: <20101017143901.GA71132@current.Sisis.de> <20101019074615.GA2183@current.Sisis.de> <20101020022946.GA23035@thought.org> <20101020052601.GA1977@current.Sisis.de> <4cbe9e9a.3qT7q8JUqJxSD8/V%perryh@pluto.rain.com> <20101020165526.GA25310@thought.org> <4CBF21EB.1080003@tundraware.com> <20101020194605.GA78565@stainmore> <4CBF4CB4.6070902@qeng-ho.org> <20101021133844.235fdc72@gumby.homeunix.com> In-Reply-To: <20101021133844.235fdc72@gumby.homeunix.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-questions@freebsd.org Subject: Re: Greybeards (Re: Netbooks & BSD) X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 21 Oct 2010 13:32:25 -0000 On 10/21/10 13:38, RW wrote: > On Wed, 20 Oct 2010 21:10:28 +0100 > Arthur Chance 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_