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Processors and the Limits of Physics
An anonymous reader writes: As our CPU cores have packed more and more transistors into increasingly tiny spaces, we've run into problems with power, heat, and diminishing returns. Chip manufacturers have been working around these problems, but at some point, we're going to run into hard physical limits that we can't sidestep. Igor Markov from the University of Michigan has published a paper in Nature (abstract) laying out the limits we'll soon have to face. "Markov focuses on two issues he sees as the largest limits: energy and communication. The power consumption issue comes from the fact that the amount of energy used by existing circuit technology does not shrink in a way that's proportional to their shrinking physical dimensions. The primary result of this issue has been that lots of effort has been put into making sure that parts of the chip get shut down when they're not in use. But at the rate this is happening, the majority of a chip will have to be kept inactive at any given time, creating what Markov terms 'dark silicon.' Power use is proportional to the chip's operating voltage, and transistors simply cannot operate below a 200 milli-Volt level. ... The energy use issue is related to communication, in that most of the physical volume of a chip, and most of its energy consumption, is spent getting different areas to communicate with each other or with the rest of the computer. Here, we really are pushing physical limits. Even if signals in the chip were moving at the speed of light, a chip running above 5GHz wouldn't be able to transmit information from one side of the chip to the other."
Same ArsTechnica article link and everything
Well, except that every other technology has hit limits, except computers! They'll just endlessly get better. Forever.
The speed of light is about a foot per nanosecond, so at 5 GHz wouldn't that set a limit of about a fifth of a foot? Pretty big for a chip.
Clockless logic circuits might be an interesting workaround for the communication problem. The other side of the chip starts working when the data CAN make it over there, for example. I don't claim to know much about CPU design beyond how the work on a basic logical level, but I'd love to hear the opinions of someone here who does regarding CPUs and asynchronous logic.
Stacking dies or some other form of going from flat to vertical will get you around some of the signaling limits. If you look back at old supercomputer designs there were a lot of neat tricks played with the physical architecture to work around performance problems (for example, having a curved backplane lets you have a shorter bus but more space between boards for cooling). Heat is probably the major problem, but we still haven't gone to active cooling for chips yet (e.g. running cooling tubes through the processor rather than trying to take the heat off the top).
I'm still waiting for estimates on when graphene will hit the consumer market and the same with optical transfer...
I'm mainly itching for graphene.
So why don't we use Alpha radiation particles?
"Even if signals in the chip were moving at the speed of light, a chip running above 5GHz wouldn't be able to transmit information from one side of the chip to the other." ... in a single clock.
So in the 1980's I was a CPU designer working on what I call "walk-in, refrigerated, mainframes". It was mostly 100K-family ECL in those days and compatible ECL gate arrays. Guess what -- it took most of a clock to get to a neighboring card, and certainly took a whole clock to get to another cabinet. So in the future it will take more than one clock to get across a chip. I don't see how that is anything other than a job posting for new college graduates.
That one statement in the article reminds of when I first moved to Silicon Valley. Everybody out here was outrageously proud of themselves because they were solving problems that had been solved in mainframes 20 years earlier. As the saying goes: "All the old timers stole all our best ideas years ago."
http://www.eetimes.com/document.asp?doc_id=1323507
http://tech.slashdot.org/story/14/08/14/1921238/can-our-computers-continue-to-get-smaller-and-more-powerful
"Impossible" is just a state of individual mind, not an objective property of anything. Anyone still believes the machines havier than air cannot fly, just because some authority said so?
Each semiconductor node shrink is faster and more power effiecient than the previous. For instance, TSMC 20nm process is 30% higher speed, or 25% less power than 28nm. Likewise, 16nm will provide 60% power saving than 20nm.
You don't need to constantly shrink everything. My computer is about 2 feet tall and wide. I don't care if it's a couple more inches in any direction. Make a giant processor that weighs 20 pounds.
Will our ever-increasing clock speeds allow us to post more and more duplicates?
http://tech.slashdot.org/story/14/08/14/1921238/can-our-computers-continue-to-get-smaller-and-more-powerful
Yet another reason to find a way around the speed of light.
Actually I've always said (jokingly) that if anyone does find a way to go FTL, it'll be the computer chip manufacturers. In fact Brad Torgersen and I had a story to that effect in Analog magazine a couple of years ago, "Strobe Effect".
-- Alastair
Engineers hate being told stuff is impossible by Scientists. It just makes them mad, and more likely to actually do it.
Congratulations, you identified the densest possible circuits we can make. That doesn't even give an upper bound to Moore's Law, let alone an upper bound to performance.
Moore's Law is "the number of transistors in a dense integrated circuit doubles every two years". You can accomplish that by halving the size of the transistors, or by doubling the size of the chip. Some element of the latter is already happening - AMD and Nvidia put out a second generation of chips on the 28nm node, with greatly increased die sizes but similar pricing. The reliability and cost of the process node had improved enough that they could get a 50% improvement over the last gen at a similar price point, despite using essentially the same transistor size.
You could also see more fundamental shifts in technology. RSFQ seems like a very promising avenue. We've seen this sort of thing with the hard drive -> SSD transition for I/O bound problems. If memory-bound problems start becoming a priority (and transistors get cheap enough), we might see a shift back from DRAM to SRAM for main memory.
So yeah, the common restatement of Moore's Law as "computer performance per dollar will double every two years" will probably keep running for a while after we hit the physical bounds on transistor size.
President Romney agrees with you too.
I see you are from the reality where the Republican Senate repealed the laws of physics. The time-space continuum is altering already.
"First they came for the slanderers and i said nothing."
The article seems to be about limitations we have not yet hit. In this context it seems misleading to point out that a signal could not travel across a chip in one clock cycle if the clock is at 5 Ghz.
First, a little background:
Processors long ago started using a technique called pipelining to increase performance. It is possible to break the hardware task in performing instructions as simple as addition into multiple stages. In pipelining one starts one or more instructions each clock cycle, but instructions take several clock cycles to complete. It is only sometimes necessary to delay instructions for results from previous instructions. This can be avoid by tricks like giving one instruction data that has been computed as part of an earlier instruction but not yet stored in memory.
My point:
In a modern cpu, an instruction maybe read from memory in one clock cycle, the data the instruction needs read in another, the actual action such as addition in yet another, and storing to memory in yet another clock cycle. Doing instructions in more steps is seen in more complex processors. Even the same website as this article has another article from 2007 which says some processors have an instruction stage where the stage simple consists of propagating the signal.
"include whole pipeline stages solely dedicated to propagating signals across the chip." http://arstechnica.com/gadgets/2007/05/the-pentium-4-remixed-taking-processors-into-the-third-dimension/
So not getting a signal across a chip in a single stage is far from being a limit we've not hit.
Humans use about 15% of their brains at any given moment, not always the same 15%, we use all of it just a bit at a time. Reminds me of that, have it all there if you need it and only turn on the parts that are needed at any given moment. Silicon evolution has done in a matter of decades what it took evolution millions of years to accomplish, at least in this one tiny area.
I see increasing emphasis in the future on unconventional architectures to solve certain problems
http://www.research.ibm.com/ar...
http://en.wikipedia.org/wiki/Q...
and a little further into the future, single molecule switches and gates.
http://en.wikipedia.org/wiki/M...
We have a ways to go, but at some point we are going to have to say bye-bye to the conventional transistor.
My rights don't need management.
The human brain is a marvel of technology. Brain waves move through it as waves of activity. It only consumes (most) energy where the wave of intensified activity is passing through it. If a 3d circuit could be made to sense when a signal is incoming then it could be more efficient. In this paradigm its no 1's and 0's, but rather circuit on vs circuit off. In addition, if you could turn those on/off cycles into charge pump circuits then you could essentially recycle the a partial of that charge and reuse it in a casade like or layered circuit. I believe Sun Micro was working on one such design, but the cost benifits were not there at the time to make it to production. Things have changed.
Maybe Markov should go back to school.. Power use is modeled as voltage squared, not as proportional.
Apologies to Markov if it is just the summary that is wrong.
Power use is proportional to the chip's operating voltage, and transistors simply cannot operate below a 200 milli-Volt level
Wow. To me it is like P~U^2. So proportional, but not linear.
And where would that 200 mV level come from? In my understanding it depends very much on the semiconductor used.
You need single isotope silicon. Silicon-28 seems best. That will reduce the number of defects, thus increasing the chip size you can use, thus eliminating chip-to-chip communication, which is always a bugbear. That gives you effective performance increase.
You need better interconnects. Copper is way down on the list of conducting metals for conductivity. Gold and silver are definitely to be preferred. The quantities are insignificant, so price isn't an issue. Gold is already used to connect the chip to outlying pins, so metal softness isn't an issue either. Silver is trickier, but probably solvable.
People still talk about silicon-on-insulator and stressed silicon as new techniques. After ten bloody years? Get the F on with it! These are the people who are breaking Moore's Law, not physics. Drop 'em in the ocean for a Shark Week special or something. Whatever it takes to get people to do some work!
SoI, since insulators don't conduct heat either, can be made back-to-back, with interconnects running through the insulator. This would give you the ability to shorten distances to compute elements and thus effectively increase density.
More can be done off-cpu. There are plenty of OS functions that can b e shifted to silicon, but where the specialist chips have barely changed in years, if not decades. If you halve the number of transistors required on the CPU for a given task, you have doubled the effective number of transistors from the perspective of the old approach.
Finally, if we dump the cpu-centric view of computers that became obsolete the day the 8087 arrived (if not before), we can restructure the entire PC architecture to something rational. That will redistribute demand for capacity, to the point where we can actually beat Moore's Law on aggregate for maybe another 20 years.
By then, hemp capacitors and remsistors will be more widely available.
(Heat is only a problem for those still running computers above zero Celsius.)
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Heat is only a problem for those still running computers above zero Celsius.
Good luck fitting your frozen computer into a laptop case or something else that can be used while riding public transit. Not everybody is content to just "consume" on a "mobile device" while away from mains power.
one day, computers will be twice as fast and ten times as big -- vacuum tubes? meet transistors.
computers can't get any more popular because we'll run out of copper. . . zinc. . . nickel -- welcome to silicon. Is there enough sand for you?
everything will stay the way it is now forever. things will never get any faster because these issues that aren't problems today will eventually become completely insurmountable.
relax. take it easy. we don't solve problems in-advance. capitalism is about quickly solving huge problems, while totally ignoring small and medium problems.
wait for it. computers will be different in twenty years. I promise.
Given that we can now have almost as many transistors as we like, but are limited by clock speed (hence heat/power), why not make a chip with dedicated circuits to implement really high-level functions such as strtol(), printf() or array-search? There might be some hardware limit (eg printf() with more than 10 arguments has to fall back to software, or arrays can only have up to 500 elements with keys and values at most 100 characters long) - but such a processor would be capable of massive performance increases.
Apparently Nature publishes any old thing nowadays, if you've got a name. "We're doomed" and drawing a few graphs culled from statistical data is not an interesting paper. Alternatives, such as graphene and optical transistors, are an interesting alternative and yet appear nowhere in the paper. It's like discussing "peak horse" in 1907 while ignoring that next door Henry Ford keeps talking up his plans for something he keeps calling a "Model T"
People have been predicting doom for CPU design, Moore's Law and Dennard Scaling for 20 years or more. And they are always wrong. Yes progress has slowed, that's true. Achieving performance gains now requires some non-linear thinking.
However consider this. We already know of a biological system, the brain, that outperforms modern CPU's (most measures, not all) by crazy factors. We're talking many, many orders of magnitude. Are we saying that this is irrelevant to CPU design? At the very least it's a challenge to match Mother Nature. And why should we not be able to surpass her in time?
However simply adapting present designs to take advantage of the 3rd dimension presents a huge opportunity. Yes the cooling and interconnects will have to be figured out. There's nothing that's unsolvable in principle though. Really the most serious challenge is the one we've always faced: Can we build it at a price the customers want? And will there be enough decent software to appeal to the buyers?
Your reasoning is false. Most AI algorithms are having a high level of parallelism which make them less susceptible to the single CPU physical limit. You can achieve incredible performance improvement on GPU and other parallel architectures.
Good luck finding enough programmers that can write code with that level of parallelism.
Most of the multithreaded code I encounter in the real world simply slaps mutexes around things, whether or not they're needed, or even applied consistently. Most of the time, the mutex could be replaced with something cheaper, like atomic operations, or even unique state-transitions on a single volatile global variable.
Your experience may differ. Maybe I just have the back luck of working with morons most of the time.
"Once we've identified and embraced our sickness, we'll have strength...and that's when we get dangerous." - John Waters
You are clueless. You live in a bubble of technology created by people infinitely smarter than you and you are happy with comic-book levels of understanding.
So you're saying that Cyril M. Kornbluth was right? Race you to Venus!
"Once we've identified and embraced our sickness, we'll have strength...and that's when we get dangerous." - John Waters
Wrong.
Wrong. Get the voltage too low and they won't be fast, but they won't necessarily stop working.
And of course, the analysis of the communications issue is also wrong.
There are obvious and non-obvious physical limitations that limit scaling, but nobody is being helped by this muddy, error-ridden presentation.
Contribute to civilization: ari.aynrand.org/donate
" Even if signals in the chip were moving at the speed of light, a chip running above 5GHz wouldn't be able to transmit information from one side of the chip to the other."
Eh?
At 300 Megameters per second, the signal would travel 6cm during one clock cycle. Just how large of a "chip" are we talking about, and how much clock skew can we design into our processor?
I call bullshit on the above statement.
But at the rate this is happening, the majority of a chip will have to be kept inactive at any given time, creating what Markov terms 'dark silicon.
When it's believed that computers only use 10% of their silicon, imagine if we could use 100% of our processors' capacity at the same time!
*mind blown*
*processor also blown*
Every ten years I hear the same thing. "We have reached the linits of processor technology" I remember hearing it in 1994 upon the arrival of the pentium.. that the x86 processor was maxed out.. during 2004, when the next gen x86 chips arrived.. Now it.s 2014.. and it's the same tune again. Suuure. They'll find a breakthrough. Count on it.