Re: Can a computer virus kill the CPU?

w_tom wrote:
Current is measured. If current is too high, then foldback current
limiting takes over.

Current is limited at somewhat above the rated value; if the load
has a low resistance then it pulls the voltage down from the nominal;
when the voltage is significantly below nominal the current limit is
reduced, further reducing voltage -- this is the foldback part of the
curve. Current can be quite low into a short circuit but must be
sufficient at all intermediate voltages to power the expected load
(which may act considerably worse than a resistor) and charge up
capacitors at the required ramp-up rate. Thus, the current into a
weak short can be 90% of the limit at 90% of nominal voltage, or 81%
of rated power all dissipated in the immediate vicinity of the screw
that went missing. (I'm assuming the actual load isn't much, maybe
because the CPU is in a power-saving mode, or the customer bought way
too big a power supply because "more is better".)

A short from any one voltage to any other voltage must not cause
damage: is required by industry standards, as is required by Intel
specs, and as was defacto standard 30 years ago.

That's not even implementable for shorts applied with power on, only
for shorts present before power so the power supply will stay at low
voltage and current. There is enough energy stored in capacitors to
vaporize a printed-circuit trace regardless of anything the power
supply can do.

Perhaps we are talking about different things. I gladly concede that
the power supply won't be damaged, or can and should be designed such
that it won't. I suppose this only costs series and bypass diodes,
and higher voltage rating on main output rectifier.

A quote is direct from Intel:

The power supply shall be capable of withstanding a
continuous short-circuit to the output without any
damage or overstress to the unit ...

Misses the worst case for the power supply transistor, though. Heat
dissipated in a linear regulator (typically used for all but the highest
current outputs) peaks at a voltage somewhat below nominal, into an
overload that isn't a full short circuit.

Again, the load may be damaged by conditions that the supply withstands.
Printed circuits aren't designed to survive much more current than they
consume.

Virus does not damage properly designed hardware.

We should stick closer to that topic. (I apologize for drifting.
Power supplies and short circuits were red herrings; no one has said
a virus can kill the power supply.)

Malware could shorten the life of hardware, perhaps dramatically,
with frequent power cycles, motor start-stop cycles, or flash updates,
or with incorrect settings of voltage to CPU or battery charger (ie
if settable for NiMH vs NiCad). (A colleague of mine once wiped out
a new tape drive with a single overnight backup with pessimal buffer
size leading to back-and-forth motion for every block.)

Should we quibble about whether destroying firmware counts?
.