From: Tim Bradshaw on
On 2006-10-12 19:31:04 +0100, kenney(a)cix.compulink.co.uk said:

> 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.

My basic physics was not confused, thanks. What I said was what I
intended to say: *whatever* you do, and *however* you propagate your
signals, they will not propagate faster than c (bar some fairly
significant changes to our understanding of how the universe works).
So the latency calculated using c is a lower bound.

--tim

From: Tim Bradshaw on
On 2006-10-12 19:31:03 +0100, kenney(a)cix.compulink.co.uk said:

> 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. That depends on a lot of factors. In all cases it will be
> considerably less than C.

It's a lower bound on the delay that any technology could have. Which
was my point, sigh.

From: Nick Maclaren on

In article <1160677731.207222.94960(a)m73g2000cwd.googlegroups.com>,
"ranjit_mathews(a)yahoo.com" <ranjit_mathews(a)yahoo.com> writes:
|> Nick Maclaren wrote:
|> > In article <1160664104.209124.194720(a)b28g2000cwb.googlegroups.com>,
|> > "ranjit_mathews(a)yahoo.com" <ranjit_mathews(a)yahoo.com> writes:
|> > |>
|> > |> Very perspicacious! What potential do you forsee for a Software IC
|> > |> implemented on a grid of processors and usable from serial codes
|> > |> (speedups from parallelism would last only for the duration of each
|> > |> call to the Software IC)?
|> >
|> > What on earth is a Software Integrated Circuit?
|>
|> It varied from one touter to the next. Think in terms of a design tool
|> that can emit logic for either an FPGA or for a grid of processors.
|> (Perhaps the tool would come with a runtime system to implement a
|> dataflow machine on a grid of processors and emit logic that invokes
|> the runtime system)

Oh, hell - THAT. Preciously little. Possibly damn all.

Yes, there are a few actions that can be speeded up significantly, but
there are very few potential uses where those dominate the time. And,
in virtually every case, 90% of the performance gain could be provided
by exposing more of the existing hardware function to the ISA.


Regards,
Nick Maclaren.
From: Peter Dickerson on
"Dennis M. O'Connor" <dmoc(a)primenet.com> wrote in message
news:1160688863.532157(a)nnrp1.phx1.gblx.net...
> <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".

Where I come from the speed of light in vacuo is denoted by (lower case) c
not (upper case) C. Hang on, I thing that was a different thread...

Peter


From: kenney on
In article <1160687715.522605(a)nnrp1.phx1.gblx.net>,
dmoc(a)primenet.com (Dennis M. O'Connor) wrote:

> All the college freshman are discovering USENET.
> And I wonder, should I just kill-file the lot of them ?

I apologise if I am telling someone how to suck eggs. However
there are a lot of factors involved. C may be the upper limit on
speed but there are a lot of other factors involved including at
Ghz frequencies the inductance of the wire.

Ken Young