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?

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...

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.

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 instruction sets are also generally 64 bit... so you end up with lesser disk space as well :) .. add the space in loading these into RAM ..

The notable exception is the Arm's thumb instruction set [embedded.com] (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.

On Mac OS X, dynamic memory has a granularity of 16 bytes. That means that if your linked list node is only 8 bytes (4 bytes data, 4 bytes pointer) then it will get a 16-byte allocation anyway, and you'll waste the extra space. Using 16 bytes per node won't hurt at all. Allocation overhead makes the standard linked list a fairly wasteful way to store data anyway.

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.

The power coming out of a chip is marginal; it's pretty much all converted to heat.

On Silicon Graphics 64-bit machines, this was solved by having two ABIs, one 32-bit, one 64-bit. You could still use 64-bit operations in either mode, but pointer size depended on the width of the ABI. This allowed you to optimise memory use on small memory jobs, but still have access to vast amounts of RAM when you had to, just by choosing the right ABI for the job.

This is an excellent observation. Please forgive me if this seems offtopic -- my primary development platform is PC, however I've got quite a bit of experience working on 64 bit.

From a developer perspective (at least in software I've worked on) programmers often do not realize that a vast number of projects took dependencies on 4 byte pointers.

Structure alignment, pointer size, etc have plagued all projects I've worked on, even after a cursory perusal at the code indicating "It looks good". Lots of bugs in porting code to 64 bit can be hidden until the right things happen.

Your particular example probably overexaggerates the point (I doubt many modern apps use a majority of memory in integer linked lists). When you think of standard server apps, most data is serialized request data which is a significant constant overhead. For the average desktop user, typing documents & email is their primary utilization of a PC, in which case it shouldn't have a tremendous effect.

That being said, there is no way your memory usage will become more effecient :-).

One additional reason that your memory will drop -- on 64 bit platforms compiled binaries become much larger. This plagues the IA64 chipset more than any other -- due to their "four simultaneous operations" (forgive me if I'm misrepresenting -- this is only through hallway chatter) binaries get an order of 2 to 4 times larger (mostly full of NOPs, no less).

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.

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.

First off power consumption for a processor = .5*C*V^2*F where c is capacitance, V is voltage, and F is frequency. So if you can find capacitance you can get a pretty good estimate of the processor's power needs.
From Intel's datasheets [intel.com]: P4 90 nm (prescott) 520-550 models 84 W of design power (what Intel recommends the heatsink be able to pull).
550-560 models 115 W of design power.

From AMD's datasheets [amd.com]: design power (measured with max amplitude and nominal voltage) is 89 watts for all power ratings 3000+ to 3700+.

I couldn't find a PPC 970 data sheet at IBM but ee times [eetimes.com] claims it pulls 97 watts, but speed was not specified. That seems consistent with the water cooling on the G5, my air cooled P4 is plenty loud.

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.

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.

In some parts in the world it does actually get that hot. Ever been to Africa? How is 32C on an avarage winter's afternoon for you? Now just imagine the summer...

Anyways, I've ony ever touched an Athlon64 once. It was a 3000+ and ran 28C at idle. Granted, room temperature was 25C (office aircon). Don't know what it would do in a hotter room.

Room temperature can make an enormous difference. My PC at home is a 2400+ AthlonXP, which ran at about 45C all winter under full load - room temperature is cold, below 15C. Now with summer approaching, it's already in the 50s. Guess I'll have to invest in a proper Thermaltake or something...

This probably depends on the compiler (and compiler flags). This is an optimization by the compiler to match memory allocation to cache line length for better performance. If you look, you'll find compiler options to allocate on whatever boundary you want.

Otherwise, it would just be a design of the memory allocation libraries (always allocate on 16-byte boundary) for similar reasons (and to lessen memory fragmentation).

Still good information to know about Mac OSX.

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.

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 [apple.com] 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 [overclockers.com.au] 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 [m0k.org] 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 [apple.com]. 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.

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?

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.