Newsgroup: it.comp.hardware.cpu
Titolo: Power Density

http://www.overclockers.com/articles197/
Intel also has put up a new statistic which is even more troubling,
something called "Power Density." Basically, it's how many watts are packed
per square centimeter. Chips are becoming smaller, but the power required to
drive them at faster speeds isn't dropping as fast, or isn't dropping at
all. You pump the same amount of power into a smaller space, and it has to
get hotter, and since there is less surface area from which heat can
radiate, it's harder to cool.
http://crd.lbl.gov/SCG/SCSeminars/20010827.html
Abstract:
 In the last decade, the microprocessor power dissipation has gone up by a
factor of ten. The frequency of operation of CMOS devices has increased ten
fold. While the input voltage and capacitance of devices has decreased, the
number of devices on a typical microprocessor die has increased by an order
of magnitude. Moreover, device miniaturization has led to integration of
cache contained at a multi-chip level to one contained on the microprocessor
die. This has resulted in high CPU core power density - e.g. 50% of a 20 mm
by 20 mm micro-processor die may contain the CPU core, with the rest being
cache. The total power dissipation from such a microprocessor has reached
100 W, and the power density is estimated to be 40 W/cm2. Extrapolating the
changes in microprocessor organization and the device miniaturization, one
can project future power dissipation of 100 W from a 1 cm by 1 cm core CPU
surface area. As multiple CPU cores become the norm, a power dissipation of
50 W from a 5 mm by 5 mm core will result in power density of 200 W/cm2!
This increase in total power, and to a greater extent the power density, has
resulted in the need for very low thermal resistance cooling solutions at
device and system level.
The system power, especially the high and mid range computer servers, has
undergone similar increase. In the high compute density data centers,
populated with rack mounted slim servers, one can pack 15 KW of power in a
standard rack. The data center is now akin to a symphony hall with 150
people per seat. For such power density, energy balance alone in sizing air
conditioning capacity does not suffice. One has to model the air flow and
temperature distribution to assure inlet air temperature to systems.

Itanium 2 Madison:
107W / 379 mm^2 = 28,23 W/cm^2
Pentium M:
25W / 82.79 mm^2 = 30,20 W/cm^2
Itanium 2 McKinley:
130W / 421 mm^2 = 30,88 W/cm^2
K8 (0,13 micron)
89W / 193 mm^2 = 46,11 W/cm^2
Pentium 4 Northwood:
82W / 131 mm^2 = 62,6 W/cm^2
K8 (90 nm)
105W / 110 (?) mm^2 = 95,45 W/cm^2 (stimati)
Pentium 4 Prescott:
103W / 112 mm^2 = 92 W/cm^2
120 (?) W / 112 mm^2 = 107,14 W/cm^2 (stimati)
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Nonostante l'Itanium, in assoluto, consumi non poco, possiede una ottima
Power Density grazie al die gigantesco che facilita la dispersione del
calore. Mostruoso invece Prescott che, nella sua "massima espressione", avrà
una Power Density incredibile, con evidenti difficoltà nel dissipare il
calore. Questo porterà alla necessaria introduzione di un nuovo sistema di
raffreddamento, contenuto nel futuro formato BTX. Il K8 in 0,13 micron non
se la cava male, mentre in 90nm ci sarà qualche problema in più.