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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: Goutam who wrote (82302)	12/8/1999 12:17:00 AM
From: Bill Jackson	Respond to of 1575913

Goutama, If you ue the CPU to drive power devices then the power consumed in the CPU will go up also. As it stands the amount of power given into the assorted busses is minimal as the chip set has all the buffers and drains a minimal current from the CPu, in addition as memory is read into the CPU is that added power input? I would say that 99.99% of the power is consumed internally as transition dumps as the transistors go from low to high and back again and again. In fact this is the reason they use more power as they go faster....more transitions=more power. Now an audio amplifier that drives a speaker can get into a situation where it where it shares the load equally with the speaker. This is classic class a operation on sine waves. The system takes 50 watts and the speakers get 25 and 25 gets eaten by the amplifier. You can go to class AB and then B and then C and get higher and higher efficiencies. Class C fully saturated is what a CPU is doing. each transistor is either on or off and tries to spend ero time in transition. Sad to say zero cannot be done as the capacitive charge must be shorted out to ground through the load for it to fall to the off state. These "dumps" of the charge on the capacitor are the measure of how much they depart from a ideal lossless system and the sum of them is the wattage consumed(plus all the internal IR drops). In addition the output transistors that clock the data to the world are a minuscile proportion of the total on the chip and they also temd to stay high/low for far longer periods and thus use less power. Countering this is the fact that they drive more current? I do not know what portion of CPU power is used by the output transistors compared to the internal logic, but it is very small. perhaps someone here can say with more precision. Bill