Re: Not too hot...
Originally posted by daveschroeder
Wrong. This is an incorrect statement that, for some reason, keeps getting repeated. As with all incorrect statements, saying it over and over again doesn't make it true.
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Power dissipation (typical) per MHz:
PowerPC 7455: 0.0355W
PowerPC 970 (1.1v): 0.0158W
PowerPC 970 (1.3v): 0.0233W
It's easy to see that, clock for clock, the PowerPC 970 consumes much less power - and therefore dissipates less heat - than the PowerPC 74xx. The current 1.8 GHz G5 numbers aren't significantly higher than a 1.0 GHz G4...it's therefore not hard to imagine the G5 making its debut in a portable machine in the future.
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I'm just realizing this thread is 13 pages long and I ain't got time to read it all, but I will add this for the people who care:
If you'd stop jumping up and down about CPU power and think about a system you'd go to someplace like Micron and look at RAM power numbers:
For
one 512Mbit chip using the current 15" PB PC133 memory---
Full speed burst access power: 120mA x 3.3V=396mW
Continuous refresh power: 5.5mA x 3.3V=18mW
For
one 512Mbit chip using the current G5 PC3200 memory--
Full speed burst access power: 450mA x 2.6V=1170mW
Continuous refresh power: 11mA x 2.6V=29mW
Multiply by the bit width of the memory bus divided by 4 (the typical bus width for a single RAM chip on a module).
These numbers are with the outputs disconnected. Now connect these higher toggle rate outputs through module traces, connectors, motherboard traces and chipset pins and your looking at a significant amount of I/O power.
Now think about the much faster system bus coming off the G5, also toggling traces.
Now think about the system controller chip, and the fact that it also has to work at these speeds.
Now remember that the G5 has no L3 cache and therefore if you slow the memory down compared to the core clock, you're going to starve it.
Are there possibly lower power memories out there rather than Micron's? Possibly. Are there ways around the memory power problems? Probably.
Will the power come down if you use slower memory connected to a slower G5? Certainly. But to bring the power in line with the current G4 lineup you'll have to slow it down a heck of a lot.
Can it be done? Certainly. Would it make a good product, I don't know but I doubt it at this point.
So please, people, start looking at the whole system and stop raving about CPU consumption like that answers all the questions.
