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

Heat Dictates CPU Design


Most enthusiasts I know have more than one computer in the house. To say nothing of what places like banks, schools, and other establishments which contain a computer for each employee within the multi-story buildings, on top of the servers needed to co-ordinate all of the traffic. Even when sitting idle these top end systems tend to draw near as much power as a 90W light bulb for just the processors alone. The picture gets much worse under load. As a result, both AMD and Intel have taken steps to bring at least the idle power draw back under control, as quite often that's the state most of them are in. AMD's Athlon64 since it's first appearance has included "Cool 'n Quiet", essentially a copy of their mobile technology using lower multipliers to drop the processor speed when not required by load to 500MHz. The upcoming 6xx series Prescotts also will include a similar feature, but with an added twist. Similar to the "Enhanced SpeedStep" found on the Pentium M chips, the voltage will also be able to be dynamically adjusted with whatever the clock speed is set to. This accomplishes nothing for the load situation, but at it's a small step in the right direction.



A larger shift though, is coming with the tearing up of the desktop roadmaps by Intel months ago. Instead of continuing down the path to creating charcoal from silicon by making another Netburst based design as the replacement for Prescott, the Pentium M will be coming to the desktop. As of yet we aren't quite aware of the form that it will take, but a dual-core implementation would surprise no one, following Intel's attempt at making lemonade from lemons with a dual core Prescott at the end of this year. The differences between the two are startling. After all, within the 130W thermal budget Intel is attempting to reach with two slowed down Prescott cores on one die, you could have six full Dothan's (21W each) running at the fastest currently available clock speed of 2.1GHz, and with headroom left over. It would be impossible to do so such a thing without fundamental changes to keep each chip from being starved for bandwidth, as well as how to fit such a thing on one piece of silicon (despite the fairly small size of each Dothan, even at 90nm creating four of them would be economically unfeasible on one die, let alone six), but it does show the possibilities when designing for power reduction from the start. To say nothing of the performance difference between the two, as a 2.1GHz Dothan is more than competitive with a 2.8-3.2GHz single Prescott.



The fundamental change in processor design is only the latest in a trend to make desktop systems more like their laptop brethren. The LCD screens that are all the rage in recent years originally were found on the first portable laptops over a decade and a half ago. While they possess a power advantage in many cases over a similarly sized (viewable area) CRT screen that is only one component in why they are replacing the older style displays. Another is the smaller form factor, giving back precious desk space, to the point of allowing wall mounting so that even the meager stands many of them come with aren't a factor in reducing available work area. That leads into the next effect, which laptops have had on their non mobile counterparts, and that is the proliferation and commercial success of small form factor computers. Reducing the size of monitors has appeared to not be enough for consumers; they also desire the tower to be reduced to that of an NBA player's shoebox. This certainly isn't perfect for everyone, after all there is only so much stuff you can put in a case that size. But considering the sales of laptop systems, the vast majority of non enthusiasts would be more than content with what can be shoved into a system this size. Laptop motherboards have become very efficient at fitting in decent amounts of functionality into something nearly half the size of the typical ATX board; this experience has had an influence in the creation of the SFF boards, as they often look very similar from a layout standpoint.

Contents

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

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