🚀 go-pugleaf

In article <x2903vvqzg.fsf@zdbaora.nat.bt.com>, Robin Smith <smithrc@zdbaora.nat.bt.com> writes:
|> Yes I agree with what you say but the point I'm making is that the RC
|> time constant is the limiting factor. Assuming you keep R constant by
|> keeping the chip cool the capacitance is still the limiting factor.
|> So you cannot clock a device faster than the capacitance allows
|> ( unaffected by temperature ).

This is exactly what I am saying (sort of).  You are assuming a constant
temperature.  I am saying that if you lower the temperature of the device (in
particular, lowering the temperature of the die of the device, rather than that
of the package), you lower the resistance, and therefore speed it up. 
Interestingly, you also lower the amount of heat it generates...
 
|> So I *assume* INTEL/AMD make their chips and rate them as to how fast
|> they can safely be run at ( with a bit of tolerance for safety ).

Yes.  Every device will be tested and 'binned' according to it's speed.  The
devices will be labelled accordingly, and the slower devices will be sold off 
at a lower price.

However, Manufacturers *do* change process technologies without telling the
customers.  It is possible, for example, that the 400 MHz parts are made up of
slower devices from the new technology (aimed at 500 MHz), plus the faster ones 
from the old technology (aimed at 400 MHz).  You won't necessarily know which
ones you've got, but the new technology devices are likely to be better for
overclocking.

|> But I also *assume* that if there is a strong demand for slow devices
|> and their fab facility is making lots of high speed devices and few
|> slow devices, then some will be relabelled as slow.  Although this
|> might not make economic sense as if there is a scarcity of slow ones
|> their price should rise to meet the demand - digression to economics.

This is true.  However, they may not derate the faster chips, so that people are
forced to buy the faster, more expensive ones.  There was a scam a few years ago
when people over in the far east were removing the labels from 486DX2-50s, and 
relabelling them as 486DX2-66s, because it was widely rumoured that Intel were 
derating 66 MHz parts to 50 MHz because their yield was so good.

Of course, they will only derate parts if they are unable to sell them at the
higher speed marking...

This is a matter for the economists/market analysts on the list to discuss, not
the engineers :-)
 
|> This is definitely my last posting about CMOS/heat/RC time constants -
|> ever!

Good. It's gone way too far off topic... <g>

|> P.S. Does Godfrey Gaston work with you? I know he disappeared to the
|> South of England to work with some silicon company.

Not AFAIK.  There are *lots* of silicon companies down here now...

-- 
David Smith                   Tel: +44 (0)1454 462380 (direct)
STMicroelectronics            Fax: +44 (0)1454 617910
1000 Aztec West    TINA (ST only): (065) 2380
Almondsbury                  Home: 01454 616963
BRISTOL                    Mobile: 07932 642724
BS32 4SQ               Work Email: dsmith@bristol.nospam.st.com
                       Home Email: David.Smith@gazpacho.nospam.demon.co.uk