Explain this to me please

flxnimprtmscl

Diamond Member
Jan 30, 2003
7,962
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So, the rough understanding I had years ago (correct me if I'm wrong on any of this) was that as the die continued to shrink chip manufacturers would be forced to up the voltage to keep the flow of electrons(?) stable on the pathways between the transistors. That was supposed to be the ultimate barrier in speed advances because the die could only shrink so much until heat got out of control due to the voltage increases.

But now it seems like each shrink in die size (65nm to 45nm for example) yields cooler, lower voltage processors. So, what am I missing here?
 

PlasmaBomb

Lifer
Nov 19, 2004
11,815
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Smaller processes lead to transistors which use less power (with a few provisos*) which if the architecture was kept the same would yield a cooler chip.

However with smaller transistors you can fit more into a given area, increasing the transistor budget for a given size of chip. Engineers and chip designers often use these "extra" transistors to add extra features to the chip, resulting in greater performance but greater heat dissipation.

Example -
Essentially you have a fictional process A where each transistor generates 1 unit of heat.
You design a wonderful chip using 100 million transistors - total heat output is 100 million units.

The engineers develop a finer process B where each transistor can run 40% cooler at the same speed or 20% faster for the same thermal specs.
Your bosses want a lot more performance out of the chip so the design bumps up to 200 million transistors - total heat output is now 120 million units at the same speed as a chip built using process A

*as features get smaller the effects of quantum tunnelling of electrons increases - this means that even when the gate is off there is a current flowing through it leading to greater heat dissipation. This was a problem with intels 90nm process, as the leakage current was significantly higher than expected. I will see if I can find a graph which demonstrated this...

** this is fictitious so if it helps you 1 unit of heat can = 1 micro Watt