11 Apr
2018
11 Apr
'18
11:40 a.m.
On Apr 11, 2018, at 2:31 PM, Jecel Assumpcao Jr. via
cctalk <cctalk at classiccmp.org> wrote:
Chuck Guzis wrote on Wed, 11 Apr 2018 11:09:23 -0700
For silicon VLSI logic circuits, yes, give or take a GHz or so. CMOS can go very much
higher in RF circuits. And if you switch to different semiconductors, you can go higher
still. People have built oscillators that get close to a THz, but those are not logic
circuits, let alone computers.
Propagation latencies also become an issue, though you can design fast computers with
substantial propagation delays if you have to. Cray did this decades ago; the basic stage
delay in the CDC 6600 is 1/20th of the clock period, and the delay on chassis
interconnects is 1/4 of the clock period. In that design, all sorts of things are
carefully paced to match the known propagation delays. But most other computers were not
designed with such complex techniques.
paul
I thought that Moore's "law" dealt
only with the number of transistors
on a die. Did Gordon also say something about performance?
That is correct. The observation that transistors would be faster and
use less power as they became smaller is called "Dennard scaling" from
1974:
https://en.wikipedia.org/wiki/Dennard_scaling
This led to the MHz wars of the 1990s. Sadly, as the isolation barriers
(the "O" in "MOS") became thinner and thinner we could no longer
ignore
leakage currents. In addition, going with lower voltages no longer was
possible as we got closer and closer to the transistor threashold
voltages. So we got stuck at 3 GHz or less.