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LOSTCIRCUITS
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| AMD Athlon64 "Venice" May Low Power be with you! | |
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(Review by MS May 2, 2005) |
| AMD Athlon 64 4000+ |
Summary
Die shrinks have long been proclaimed as the way to lower power and higher speed. On the other hand, for about as many years, the issues of leakage currents has been known, that is, with every die shrink, the ratio between leakage and operating currents has gone in the wrong direction at an alarming rate. New process technologies targeting the substrate rather than the actual interconnect process are, therefore, becoming the focus of R&D;, from Low-K substrates as used in graphics processors to Silicon-On-Insulator, a technology developed by IBM in the 1950ies.
On the transistor design level, improvements have been made by straining the silicon to physically alter the lattice geometry and thereby optimizing the conductivity between source and drain. Starting out with a relatively simple Silicon-Germanium epitaxy, we are looking at uniaxial compression and stretching for PMOS and NMOS devices, respectively, to speed up the currents and reduce power consumption at the same time. Finally, the concerted efforts in substrate and device technology were supplemented by some functional tweaks on the memory controller and instruction sets to result in a beautiful piece of process engineering and design named "Venice".
We have taken four different cores, that is, ClawHammer, NewCastle, Winchester and Venice for a comparative review of their processing vs. electrical power characteristics and the results pretty much blew us away.
Nothing can probably sum the dilemma that the computer industry is facing as dramatically as the picture below. We have witnessed a huge increase in computing power, along with increasing numbers of computers worldwide and all of that amounts also to some very frightening numbers when just looking at the power figures as landmarks for where the computer stands in our daily life. Even more frightening is the fact that the numbers shown are based on the average power consumption of computers in 2001 along with the average number of computers at the same time.
Power consumption of PCs in 2001 ---- and rising (Picture courtesy of Dr. Avi Mendelson, Intel Corp.)
Four years later, CPUs are no longer content with some 15W peak power consumption, in fact, the latest processors in the desktop market are pushing some 130W as the thermal envelope while at the same time, the growth of computers worldwide has exceeded by a multiple the already scary growth figure of the human population. In other words, cautiously we project the current power consumption of all computers running somewhere in the order of at least 20 Hoover Dam power plants � reason enough to really start thinking about power reduction wherever possible.
Power consumption of any computer is the sum of the power draw of all individual components, starting from system memory over the various storage media to the central processing unit, which after all, still eats the lion share of the total power. Likewise, it also produces the most heat. Power consumption and heat dissipation are related but the relation is not necessarily linear. That is, overall, power consumption is always higher than thermal dissipation, after all, against common knowledge, CPUs were not primarily designed as space heater substitutes.
Processor power consumption varies with load. That is, the more work a processor has to do, the more power will it consume. By extension, it will produce more heat. More heat, on the other hand, will cause the efficacy of the processor to decrease according to the thermal derating of the unit. By extension, this also means that under constant load but with the temperature increasing, the power consumption of the processor will increase and that will, in turn, increase the thermal dissipation as well. Luckily for anyone involved, this is not an endless death-by-heat spiral, there is some equilibrium that will be reached when the different slopes of temperature derating and heat dissipation cross. As a rule of thumb, we are looking at roughly 30% increase in power consumption over some 125 centigrades increase in die temperature. For the desktop environment, this amounts to some 10% increase in static power if the temperature increases by some 40 degrees, for example from 30 centigrades at the onset of a given load to 60 centigrades after leveling out.
We could go into a lot more gory detail on the different aspects of power here but suffice it to say that power measurements need to take into account a whole slew of factors, otherwise they may serve as rough guidelines only.
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Athlon64-3500+ (Venice Core) |
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