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D'arcy Lemay · 01-26-2005 · Category: Tech-planations

The Mobile Shift




The Pentium M obviously possess at its heart all of those nifty features for lowering power requirements that are normally hacked into a desktop chip, but it also has a few other tricks up its sleeve. One of those is an ability to dynamically power only certain sections of the cache, keeping the amount of circuitry on at any one time to a minimum. While each section of cache itself does not suck up much power, there is a fairly significant amount of it on both revisions of the P-M (Banias 1MB, Dothan 2MB). This is really only going to apply at times when the chip is idle or under light load, but for the vast majority of users, that's how the CPU sits a good chunk of the time it is on. Another piece of electrical trickery to lower the juice required is dynamically adjusting the voltage input to the CPU. As the clock is moved down at idle, so too is the voltage since it is able to remain stable under that situation. The chip also is designed to perform capably while retaining (relatively) low clock speed and voltage levels, as these are generally two factors that affect power draw on a large scale. The Israeli group somewhat "cheated" on this one, by starting with the P6 core used in every Intel desktop and mobile processor from the Pentium Pro up till the "Tulatin" Pentium III, and tweaking it from there as opposed to starting from scratch. From the results though, this was a brilliant idea by the design engineers. It cut down on the design time for the core, and allowed them to focus on other aspects of the processor.



Where does this fit back into the desktop picture though? Currently the high end 130 and 90nm chips have issues with outrageous heat dissipation, to the point where the fastest Pentium4 processors aren't capable of running their fastest speed under load without aftermarket cooling being added. It isn't just Intel either, though this currently is less of an issue for AMD. The fastest IBM PowerPC processors being used in the PowerMacs require a form of liquid cooling to operate. Is this a sign of the coming apocalypse? Not quite, but it certainly is disturbing when a product ships with a cooling system incapable of allowing it to run at its highest velocity without setting off its internal methods of survival. As well, the cost of powering a large number of computers no longer becomes insignificant.

Contents

  1. Introduction
  2. The Mobile Shift
  3. Heat Dictates CPU Design
  4. Conclusion

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