🚀 go-pugleaf

In article <7000@pt.cs.cmu.edu>, lindsay@MATHOM.GANDALF.CS.CMU.EDU (Donald Lindsay) writes:

> 
> This is well-known as one of Seymour Cray's concerns. In the Cray-1,
> he was worried that standing waves could develop in the copper ground
> plane of a circuit board. His answer was to make a machine with power
> demand that was (I believe) completely independant of the data
> flowing through it. 

This was a worry one machine before the Cray-1 - the Cyber 7600.

(stuff deleted)

> CMOS isn't like that. It's asymmetric, and cares about transitions:
> 0=>1 takes more power than 1=>1. So, one can write worst-case
> programs, which generate on-chip noise (mass transitions on the wide
> datapath), or which generate board noise and heat (mass transitions
> on the address and data pins). I'm not sure what cache activity
> generally produces the most heat: it may depend on implementation.
> 
(more deletions)

> CMOS is wonderful, but the ECL/GaAs/BiCMOS folks talk an awful good
> fight about how it's a different world on the other side of 50 MHz.

Sure is.  The ETA-10 had this problem in spades.  This is why the
ETA-10 air-cooled was limited to about a 12-13 ns clock (~80 MHz)
before fratzing.  There was a 15ns model (the model R) under development
when CDC killed it.

The liquid-nitrogen cooled behemoths could have gone just about as
fast as one dared.  The successor machine to the ETA-10G (the I
model) was to be around 5 ns (200 MHz) in a breadbox-sized container
of liquid nitrogen.  Folks were talking about a 500 MHz board, but
that was just hall talk.

Note, the parts were ASIC CMOS.

Still true today that the power required for the actual processing
goes down, and the power required to cool the thing goes up.  Neil
Lincoln often joked that the ultimate machine would be thimble-sized
and require one one-zillionth of a watt, but the cooling of the
thimble would require one zillion watts.

Rob
Rob

-- 
Rob Peglar	Control Systems, Inc.	2675 Patton Rd., St. Paul MN 55113
...uunet!csinc!rpeglar		612-631-7800

The posting above does not necessarily represent the policies of my employer.