ethernet76 said:
Ok. Here is how it works, as I use to overclock my P3 to ridicous speeds and saw heat increase significantly.
When you increase the clock cycle, you increase the amount of energy flowing through the chip and more and more of the energy escapes as heat. This is some sort of non-linear equation deal.
specifically, wattage is calculated by voltage * amperage. Amperage is often referred to as "current". A cpu that uses 1.5 volts will draw more amperage if you increase the clock frequency or if you actually use it. That's why chips get hotter when they are under load. One way to overclock a processor more is to increase the core voltage. This usually allows you to get a higher clock out of it than you otherwise might. This has the nasty side effect of REALLY driving up the wattage though.. Just think about an increase from 1.5 to 1.8V.. that's +20%. With a chip that would normally be rated at 1.5V and 50 watts.. a move to 1.8v (if all other things remained the same) would mean you are at 60w right away. Then you start increasing the clock....
Theoretically, if you ran the processor slow enough, you wouldn't need a heatsync.
Now compare this when I got the 600 to run at 933. To keep it at safe running temperatures I had the side panel door open and a 14-inch industrial fan blowing inside the case. It still ran at about 170 degrees F.
right, the issue here is, how much current the chip needs to draw at that frequency. You're lucky you got it to run that fast without upping the voltage.
While the 970FX is more efficient than the original 970, it isn't a huge improvement.
Well, there is a decent improvement in the new processor, but IBM is still working out issues with the new processor. The smaller the process (the thinner the gates), the more likely you are to run into current bleed and signal cross talk. You can actually get electrons hopping the traces.. effective screwing everything up. IBM expected a lot of current bleed.. the more current bleed, the more draw the chip will have.. so the hotter it will run. This is a problem with the Intel process.. one of the reasons the Prescotts are HOTTER than the .13 micron Northwoods. IBM actually had a lot of unexpected problems with signal crosstalk, something that caught them off guard.
Now considering the following. Take 1000 people put them in a 130 by 130 foot room. Then, take the same 1000 people and put them in a 90 by 90 room. Which room is going to be hotter?
So in effect, the chip generates more heat because the high clock speed in a smaller space. The chip has an effective surface area of 8100 nm squared. The original has twice that surface area.
this is where your argument has serious issues. The new processors AREN'T 8100 nm^2. That's be REALLY small. They are actually 66 mm^2. The _process_ is .09 micron (90 nm). That's a reference to the size of the features on the die.. not to the size of the processor.
In comparison, I *think* the old 970 was around 100 mm^2. An Athlon64 with 1MB L2 is about 170 mm^2.
Your basic argument is somewhat sound, you just have problems with the details.
The comment from the Apple guy is accurate though. I'm just making up numbers here for an example so bear with me..
say a 2.5GHz 970fx chip runs at 80 watts. That's 80 watts disipated from a 66 mm^2 surface or about 1.2 W/mm^2. An Athlon64 3400+ might also put out 80 watts, but the surface is around 170 mm^2. That's less than 0.5 W/mm^2. Even though both chips are generating the same waste heat, the PPC 970fx is producing 2.5X as much for a given area. That would mean that you need a cooling solution that removed heat 2.5X as efficiently (quickly) with the 970fx as you'd need with the Athlon64. Liquid cooling is more efficient.
Other comment... As for the questions regarding why a 2.5 would be so much hotter than a 2.0.. there could be a lot of reasons.
Firstoff.. it runs faster. More current draw.
Second, it may run at a higher core voltage. it isn't all that uncommon to see CPUs with different rated core voltages even if they are from the same family. The speed bin from the manufacturer is all about stability. If a chip can run stable at a given speed, it's bin'ed at that speed. If they can get some chips to bin a 2.5GHz at a slightly higher core voltage, that's a valid sort. The 1.8 GHz parts may not run stabily at a much higher clock speed even if the core voltage is upped.
We won't know what the core voltages are until IBM lists part specs on the 970fx chips though.
edit: One last point...
back to why liquid cooling is so much better than just air cooling. A lot of people pretty much answered that question by pointing out that the liquids transfer heat quicker than air. I just wanted to add that air is a pretty Poor thermal conductor. The only reason we survive as air cooled creatures is due to the constant evaporation from our skin.. especially when it's really hot. Air is such a bad coolant that it's often used as an excellent insulator. If you look at just about any insulation.. like the fiberglass insulation in most homes or even a down winter coat, it's the dead air between the fibers/feathers that actually insulate. If you put fiberglass insulation in a flat bag and sucked all the air out of it, it'd have a really terrible R value (which, coincidentally is how many times better the insulation is compared to un-trapped air of the same thickness)
So, Air sucks as a coolant.. why does it work so well for things like really hot computer chips and even radiators. It's all about surface area. Computer heatsinks and radiators are designed to provide a vastly greater amount of surface area to the air that is flowing across it. A radiator has even more surface area... there are all those coils of (typically) aluminum that the liquid flows through.. the radiator also has the heat spread out because the coolant flows all through the radiator. Air is still a terrible coolant, but if you flow that fresh air over, say, 100x more surface area than the face of the chip.. and if you do a good job of spreading that energy out over the fins (that is, circulating the coolant to all parts of the heat sink/radiator), it does OK.
In the end, it isn't the liquid that makes the new G5s system so much more efficient, it's the radiator the coolant flows through. If the radiator didn't disperse more heat than a carved slug (heatsink), and if the coolant flow didn't allow better dispersion of that heat (energy),.. the ambient temperature of the coolant would rise too high and the water block wouldn't do anything at all.
