10-10-2009, 05:30 PM
As you noted, the Late 2005 quad mac pro outputs less heat than the G5 I was citing, yet it uses more power. That similar to what I'm saying about the Xeon - just be cause it's "rated" at more power, doesn't mean it outputs more heat. And in the test, even if adding more RAM, video card... to the Mac Pro, it still has to almost double its default BTU output to match the G5.
You're still making an inaccurate comparison. The Xeon uses far fewer watts than the G5, so it's going to output less heat than the G5. That is by far the biggest difference between the two.
And you can't use theoreticals here. You have to take into account things like the old power supplies being much less efficient. There's power loss all along the way. The greater power loss, the greater the heat output. All that energy doesn't come out as heat, it comes out as other forms of energy too.
The Mac Pro is a far more efficient machine. Again, hence why Apple had to add liquid cooling to the G5, but not the Xeon. The G5 produces more heat.
The TDP of the Xeon is about 130W. It's tough to find G5 numbers, but the best I could come up with was that a single G5 2.5 CPU used 125W. Since they came in dual configs, that's 250W. The 2.7GHz obviously used more.
Compared to the 250W+ of a a pair of G5 processors, I still think 10-12W of a pair of DIMMs is not much. You'd have to have 10 pairs in a Mac pro to equal the heat difference between a G5 and a current Xeon.
Not only that, but I think people were more apt to put more, smaller RAM chips in a G5 than in a Mac Pro.
Yes, I agree, if he put a huge power hungry video card in that does have potential to create a fair amount of heat. Still not as much extra heat as the processors, but a fair amount. The most powerful video card Apple offers uses up to 236W. For the G5, it was about 123W. So a 100W+ difference - still less than the difference between the G5 power usage and the Xeon.
I still don't think it would be easy to do that.
As you look at the specs and see the comparatively, low power usage of things like the video card, ask yourself how the G5 would still use so much power and through a process of elimination, you can see it's the processors.
On a side note, I have a nehalem machine here, GTS240, 4GB RAM... and it puts out far less heat than the G5 2.7, 9650, 4.5GB RAM... I just sold.
You still do not get it, for every 100 W of power going into a computer, about 100 W is going to come out as heat. That is HEAT not the CPU TEMPERATURE, it does not matter whether it is shedding that total amount of heat off a CPU surface at 65 C or at 40 C. But, then you are not the first person to confuse the concepts of temperature and heat.
You're still making an inaccurate comparison. The Xeon uses far fewer watts than the G5, so it's going to output less heat than the G5. That is by far the biggest difference between the two.
And you can't use theoreticals here. You have to take into account things like the old power supplies being much less efficient. There's power loss all along the way. The greater power loss, the greater the heat output. All that energy doesn't come out as heat, it comes out as other forms of energy too.
The Mac Pro is a far more efficient machine. Again, hence why Apple had to add liquid cooling to the G5, but not the Xeon. The G5 produces more heat.
The TDP of the Xeon is about 130W. It's tough to find G5 numbers, but the best I could come up with was that a single G5 2.5 CPU used 125W. Since they came in dual configs, that's 250W. The 2.7GHz obviously used more.
And you better rethink your "RAM doesn't really put out much heat", if you are going to be figuring out cooling requirements for a machine. Typical is around at least 10-12 W when active per 2 GB DIMM of the kind used in the Mac Pro's, less for the type of RAM used in G5's.
Compared to the 250W+ of a a pair of G5 processors, I still think 10-12W of a pair of DIMMs is not much. You'd have to have 10 pairs in a Mac pro to equal the heat difference between a G5 and a current Xeon.
Not only that, but I think people were more apt to put more, smaller RAM chips in a G5 than in a Mac Pro.
The final big difference is going to be in that PCI Express bus, where the Mac Pro allows up to 300 W usage, and for the higher power video cards supplements that with a direct connection to the power supply. The G5 max'd at 150 W for the video card.
Yes, I agree, if he put a huge power hungry video card in that does have potential to create a fair amount of heat. Still not as much extra heat as the processors, but a fair amount. The most powerful video card Apple offers uses up to 236W. For the G5, it was about 123W. So a 100W+ difference - still less than the difference between the G5 power usage and the Xeon.
One, it does not address my contention that max'd out a Mac Pro can meet or exceed the power requirements and heat output of a G5, and Two, ignores that you can add less to the G5 before the system runs out of space and power.
I still don't think it would be easy to do that.
As you look at the specs and see the comparatively, low power usage of things like the video card, ask yourself how the G5 would still use so much power and through a process of elimination, you can see it's the processors.
On a side note, I have a nehalem machine here, GTS240, 4GB RAM... and it puts out far less heat than the G5 2.7, 9650, 4.5GB RAM... I just sold.