How Many Processor Cores Are Enough?
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From: kenney on 12 Oct 2006 14:31 In article <k2l104-v7b.ln1(a)osl016lin.hda.hydro.com>, terje.mathisen(a)hda.hydro.com (Terje Mathisen) wrote: > I am sure Dennis really appreciated being told about the speed > of light, and how it varies in different materials. I get upset when basic physics is confused. C should not be used in regard to propagation delays in anything but vacuum. For a start in most cases we are not talking about EMR but electrons or holes. Until you get optical chips operating in a vacuum C is wishful thinking. Ken Young
From: Del Cecchi on 12 Oct 2006 15:36 kenney(a)cix.compulink.co.uk wrote: > In article <k2l104-v7b.ln1(a)osl016lin.hda.hydro.com>, > terje.mathisen(a)hda.hydro.com (Terje Mathisen) wrote: > > >>I am sure Dennis really appreciated being told about the speed >>of light, and how it varies in different materials. > > > I get upset when basic physics is confused. C should not be used > in regard to propagation delays in anything but vacuum. For a > start in most cases we are not talking about EMR but electrons or > holes. Until you get optical chips operating in a vacuum C is > wishful thinking. > > Ken Young Sorry, I get really upset when physics geeks think conduction in wire is related to electron movement. Sorry, it's EM fields. And if the wire is on the surface, some part of the field is in air which is almost as good as vacuum with respect to electromagnetic fields, at least until you get to large numbers of GHz. -- Del Cecchi "This post is my own and doesn?t necessarily represent IBM?s positions, strategies or opinions.?
From: Dennis M. O'Connor on 12 Oct 2006 17:15 "Terje Mathisen" <terje.mathisen(a)hda.hydro.com> wrote ... > Tim Bradshaw wrote: >> On 2006-10-12 11:14:10 +0100, kenney(a)cix.compulink.co.uk said: >>> Actually you can, the speed of light depends on the medium it is >>> travelling in. C is the speed of light in a vacuum and should only be >>> used for that. >> >> I'm sure Dennis meant the speed of light in vacuo: I certainly did. >> > I am sure Dennis really appreciated being told about the speed of light, > and how it varies in different materials. And arrangements of materials, like transmission lines. <sigh> It's the start of a new school year, isn't it ? All the college freshman are discovering USENET. And I wonder, should I just kill-file the lot of them ? Nah. I haven't even kill-filed "N", so why do them ? -- Dennis M. O'Connor dmoc(a)primenet.com
From: Dennis M. O'Connor on 12 Oct 2006 17:27 <kenney(a)cix.compulink.co.uk> wrote... > In article <egl6l3$69q$1$8300dec7(a)news.demon.co.uk>, tfb(a)tfeb.org > (Tim Bradshaw) wrote: > >> I'm sure Dennis meant the speed of light in vacuo: I certainly >> did. > > It is not something that should be used for calculating delays > on chips. C is one of the fundamental constants. It figures into a lot of calculations, for example, calculations of the propogation of signals on transmission lines: IIRC velocity = C/SQRT(dielectric_constant_of_insulator) -- Dennis M. O'Connor dmoc(a)primenet.com
From: Dennis M. O'Connor on 12 Oct 2006 17:34
<kenney(a)cix.compulink.co.uk> wrote ... > In article <k2l104-v7b.ln1(a)osl016lin.hda.hydro.com>, > terje.mathisen(a)hda.hydro.com (Terje Mathisen) wrote: > >> I am sure Dennis really appreciated being told about the speed >> of light, and how it varies in different materials. > > I get upset when basic physics is confused. C should not be used > in regard to propagation delays in anything but vacuum. No one here used it for anything but that. You just assumed that people were talking about the propagation speed of signals in other materials. You assumed wrong. Have you forgotten that the "speed of light" in a material is IIRC equal to C/SQRT(dielectric_constant) ? > For a start in most cases we are not talking about EMR > but electrons or holes. Only in the devices. But device delays no longer dominate in cutting-edge designs. Wire delays do, and that's EM fields, not electron movement. > Until you get optical chips operating in a vacuum C is > wishful thinking. No, C is the speed of light in a vacuum, regardless of whether optical chips are operating in a vacuum or not. It is not, as you claim, "wishful thinking". -- Dennis M. O'Connor dmoc(a)primenet.com |