--- On Sat, 1/23/10, Dan <[email protected]> wrote:

> From: Dan <[email protected]>
> Subject: Re: Why are you (still) using PowerPC-based Macs?
> To: [email protected]
> Date: Saturday, January 23, 2010, 9:30 AM
> At 2:45 PM -0800 1/22/2010, John
> Niven wrote:
> > Like all good rumor there is truth in some of this.
> > 
> > Semiconductor line widths have become so small that
> the operating voltage has had to be reduced constantly to
> combat leakage and NBTI effects. Having a overvoltage
> condition is VERY hazardous to a cpu's life. We in the
> semiconductor industry [...]
> 
> Are smart enough to put diodes and such in there to protect
> the chips from such conditions.  And besides, the power
> managers in products such as Macintosh are designed so they
> just can't crank out so much power as to fry the chips etc.

http://www.semiconductor.net/article/205454-NBTI_A_Growing_Threat_to_Device_Reliability.phphttp://www.semiconductor.net/article/205454-NBTI_A_Growing_Threat_to_Device_Reliability.php

We DO have circuits to protect against ESD, but I'm talking about much subtler 
conditions that lead to performance degredation of the transistors themselves. 
The practical upshot is the speed of the parts degrades, so since thats fixed 
by the clock, the cpu will eventually malfunction, happening first when it is 
hot.

We have to sell the parts at a lower rated speed to allow a "Useful life" 
before the speed is no longer met.


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