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What Makes Apple's Power Mac G5 Processor So Hot
An anonymous reader writes "58 million transistors can drive a lot of power. Apparently, Apple appreciated the choices IBM processor architects made when designing the 970 family. This article provides the 64-bit architecture big picture for the 970 family (A.K.A. the Power Mac G5) and the critical issues in IBM's 64-bit POWER designs, covering 32-bit compatibility, power management, and processor bus design."
One side-effect of 64-bit computing that I don't hear a lot of discussion about is the increase in the size of a pointer. A standard implementation of a linked list of integers will now be 50 to 100% larger (depending on if you use 32 or 64 bit integers), simply because the pointers take up more space. If I bought a 64 bit system, simply because it's the "Best", but only got 1GB of RAM, I have less useful memory, because the pointers take up all of my physical RAM. Do the architects of these systems take this into account?
Sometimes I doubt your committment to SparkleMotion!
I'll probably get modded down for saying this, but I have Karma to burn...
That article is some crybaby whining about how expensive the G5s are. "Apple is so dumb. Why would anyone pay that much for a CRAP computer," is what the article sounds like. I think that guy needs to take his superior knowledge elsewhere and try some benchmarks ("512K of cache isn't competitive for $3000")... apparently it is because it's winning benchmarks and people are buying them. Just because you can't afford it doesn't mean it's a bad computer (doesn't mean it's a good computer either). This guy needs to grow up and write an article with facts instead of emotions...
My other car is first.
I recently upgraded to a 754-pin Athlon64 3000+, and the hottest it's ever been is 51 C, a few degrees more than the room temperature of 43C. On a cooler night, with 100% CPU load for ~2.5 hours [2-pass XviD encoding], it peaked at 47 C. Quite impressive.
Use ISO 8601 dates [YYYY-MM-DD]
Does anyone have the numbers to compare how many watts of power the G5 uses vs a similar AthlonXP or AMD64? Ie, I'd like to see how a 2.0 or 2.5 GHz G5 compares to a 2.0 or 2.5 GHz AMD processor.
The notable exception is the Arm's thumb instruction set (it's cool).
The sad part "my address bus is bigger than you" is going the "I have more MHz than you" way soon as parallel CPUs (mulit-core or otherwise) become cheaper.. 90% of our tasks are better done parallel than using a single fast chip . Hell , half of the tasks really don't need anything beyond a 300/400 mhz clocks.Quidquid latine dictum sit, altum videtur
Wattage only tells you how much power the CPU consumes, it doesn't tell you how much heat it gives off.
Power consumption = Power In
Power In = Power Out + Heat
What you want to know is how much heat is given off.
Your iMac G5 has two fans. Not much space left for additional cooling, really, without interfering with the current cooling setup.
Your PowerMac G5 has nine fans. Again, not much space left for additional cooling without interfering.
And get this, the PowerMac G5 already uses a liquid cooling setup. The only possible additional mod is to hook the current setup to a resevoir and radiator on the outside of the case, as the inside already has a radiator per CPU and something like a 120mm fan per CPU.
GPL Deconstructed
It's not a matter of total heat dissapation as much as the fact that the head is dissapated in very small areas of an allready tiny chip.
The PPC970FX actually doesn't produce that much heat compared to the current AMD and Intel crop, only dissapating 54W typical at 2.5Ghz (albiet a good deal higher at peak). But due to it's smaller die, it has to dissapate that heat from a smaller area, thus requiring a cooler heat sink to dissapate it into to maintain the same die temperature.
It's basic thermodynamics, but something geeks often overlook.
The G5 2.5 dualie I just received puts out waaaaay more heat than any computer I've ever seen. I had to move it out from under my desk to the side to allow the heat to escape. It was much more than a foot warmer.
cat
It used to be that Mac fanatics would be proud about how little current the PPC used -- and consequently how little heat it gave off -- when compared with the Intel-style architecture. Guess we can't make that argument any more.
Now that G5's are liquid cooled, it makes me wonder if a 2.5GHz G5 is *really* a 2.5GHz G5, or if it's an overclocked 1.8GHz chip. You know, overclockers really pump things up with cool liquid cooling stuff. What's the fastest a 2.5GHz G5 could run with a traditional cooling system, like a fan and heatsink?
Oh, one more thing before I'm modded as a troll: my G4 PowerBook is my 8th Macintosh. What I'm asking is genuine curiosity.
--Jim (me)
Its not that apples (and most likely some of the x86 based computers too though I haven't really looked into it) aren't supercomputers. Its just that given the current definition of a supercomputer its just not that amazing anymore. Maybe its the definition that needs to change rather than you being upset at people that follow the definition.
"You can now flame me, I am full of love,"
Well, a very similar trade-off applies to other processors in the same league e.g. high-end workstation and lower-end server (Opteron, Xeon). The comparison made in the article is between the 970(fx) and Power4/5.
for literal heat, this puppy is pretty hot.
my dual 2.5GHz PowerMac G5 idles at 52C (125F) on CPU A and 50C (122F) on CPU B. the memory controller is actually one of the hotter things, it idles at 62C (143F). however, it's not the hottest thing, of course: at full load (DVD rip+encode or playing 15 videos at once + MP3 + tasks + flicking around Exposé) both CPUs have hit a max of 83C (181F) (the computer is supposed to automatically sleep around 90C or so).
so why so effing hot? i mean, this idles at the max temp my athlon 2500 peaks at! it certainly idles at a hotter temp than it needs to, but i have no problem with that: the system runs the fans dynamically to keep the noise down, so at idle it's not as cool as it could be. the difference in noise in my room when i sleep the athlon is ridiculous - the G5 sounds like a slightly loud external hard drive that's spun up. the system also has a liquid cooling system to quench the processors. this seems to just keep the processors within their range. the value that i see in it is response to new heat - the CPU temps flick around a lot and are very responsive to load and the loss of load. after ramping up the CPUs to >80C, it take about three or four seconds after the load drops for the CPU temps to drop 15-20C, then maybe a total of ten or twelve seconds to drop to idle temp.
for some real-world perspective... a DVD rip+encode with HandBrake with using ffmpeg engine, MP3 audio, 2-pass encoding, and gunning for your average 700MB movie time (800-1300kbps?) takes slightly less than the length of the DVD. an hour and a half long movie took about and hour and fifteen minutes to get on to my hard drive. MP3 ripping in iTunes will run up to 28x, but it's not fully loading the processors so i wonder about a drive read bottleneck. the first night i got it, i was at a loss for how to really test the speed on it, so i just decided to open up a shitload of videos. basically i played a DVD (fluff, the GPU does that), opened up something in VLC, opened up about 13 videos in QuickTime of various sizes and formats, played some MP3 music (fluff again, that's ball sweat of a cutting edge proc), and still had enough processing power to comfortably navigate files, chat, browse web pages, and flick around Exposé. around all of these things plus one is when a few of the videos would start stuttering and expose would start dropping frames to keep collapse speed uniform. anything past this would really start robbing time from videos.
all in all? it's fast. it's quiet. it gets hot, but it takes care of itself. coming from a 375MHz G3-upgraded PowerMac 7600 (vintage '98), i'm not doing too shabby. i just decided i'd scramjet at mach 7 to the top of the pack and then sit there for another few years.
- emilio
neurostyle dot net - it's all in your head
What if our universe is only a simulation running on a computer in another universe?
Maybe it's possible to disprove this based on the idea that the other universe would need to be physically larger?
My other first post is car post.
They use liquid cooling because it's harder to disapate the heat from the small 90nm core. The CPU's don't use much power, it's just that the heat they do produce is concentrated in such a small area. Better cooling is required to disapate this heat.
90nm transiters require less power then their larger counterparts. The problem is, for the same die size they use more power. So you end up with a relatively low power CPU that requires massive cooling.
Apple and IBM had a lot of problems because they expected their new CPUs that consume less power to be easy to cool. They were wrong. For each square mm, more heat must be disapated.