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Topic: What causes heat in a CPU? (Read 1 time) previous topic - next topic

cjdelphi

IS it simply the number of transistors? or the Switching speed?....

eg which would generate more heat?,

a 4 core processor each core clocked at 50mhz.

or

Single core processor clocked at 200mhz?




Osgeld

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CrossRoads

Not enough info provided to say.

The number of transistors switching at high speed is what causes the  heat.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

retrolefty


IS it simply the number of transistors? or the Switching speed?....

eg which would generate more heat?,

a 4 core processor each core clocked at 50mhz.

or

Single core processor clocked at 200mhz?






Most modern processor are based on cmos logic which have very low static current consumption. Most of the power dissipated in the transistors is during the transitions from high to low and low to high, and so the faster the switching speed the more transition made over a fixed duration of time. So speed would have a bigger impact then sheer number of devices. At least that is my opinion. You can kind of see the effect in a typical Atmel datasheet showing current consumption Vs clock speed which have quite a range with the same number of transistors.

kf2qd

The faster the processor runs the faster the transistors have to switch from on to off.  There is some limit to how fast the transistors can switch, so there is some overlap of transistors switching on and off and those overlaps can look like short circuits. As the transistors are in transition for on to off they look like resistors. Current flowing through resistors produces heat.

AWOL

Quote
The number of transistors switching at high speed is what causes the heat.

But that's not going to be a problem at 50 or 200mHz.  ;)

winner10920

but then why would overclocking generate heat if the faster it worked the cooler? I think as speed approaches the transistors limits they spend more and more time in the transition state causing heat, overclock it too much and the transistor doesnt saturate and that's where unreliability comes in when its supposed to be a 1 and it doesn't quite reach there before its scheduled to

udoklein

A FET transistor gate is basically a capacitor. Charging / discharging the gate will turn electrical energy into heat no matter how long the transistion state. Increasing the frequency will cause more charge / discharge cycles. It also implies that you have to increase the voltage in order to charge / discharge fast enough causing even more heat.
Check out my experiments http://blog.blinkenlight.net

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