[CUBE] memory question

[Joseph B. Gurman]

     Gnarlodious spake thus:

>  > and a faster processor adds lots of heat.
>Huh?
>Just last week someone said the newer electronics are more efficient than
>older electronics, so power consumption is not significantly higher.
>
>My understanding of physics is that power=heat, so what's wrong with this
>picture?
>
>If we could just get the numbers on the processor upgrades. . .

     At least two things affect how much power a CPU chip uses. For a 
given process size (typical transistor size), heat dissipation goes 
something like the square of the clock speed. As process size gets 
smaller, though, the amount of heat dissipated is less for identical 
clock speeds, so generally (Pentium 4's are a glaring exception) 
CPU's with smaller process sizes run cooler. The 7457 (fabbed at 130 
nm), which is what PowerLogix (at least) is offering in its Cube CPU 
upgrade kits, dissipates < 20 Watt at 1.4 GHz, while the 7455 (180 nm 
process size) would dissipate ~ 3 times as much heat at the same 
speed, if it can be forced that high.

     The original CPU in the Cube was a 7400 or 7410. If the 7410 
could have been run anywhere near 1.4 GHz, it would dissipate ~ 40 W. 
As an added improvement, the 745x's are capable of four instructions 
per clock cycle vs. three for the 7410; if Apple takes advantage of 
that, many things could seem even faster.

     ....or such is my understanding of the CPU power dissipation bidness.

						Joe Gurman
-- 
"I love deadlines. I love the whooshing sound they make as they go by."
                                                             - Douglas 
Adams, 1952 - 2001

Joseph B. Gurman, NASA Goddard Space Flight Center, Solar Physics
Branch, Greenbelt MD 20771 USA