Author Topic: Why have CPU's stopped at ~1.8 GHz?  (Read 15173 times)

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Online T3sl4co1l

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #25 on: May 27, 2017, 06:41:45 pm »
If they go to a different semiconductor, I'm curious how much dev time and cost they're going to incur on that.

It's one thing to change everything about your fab and dial in good yields again; it's a whole 'nother thing to do that AND do it at the finest pitch yet.

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Offline coppice

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #26 on: May 27, 2017, 06:46:10 pm »
If they go to a different semiconductor, I'm curious how much dev time and cost they're going to incur on that.

It's one thing to change everything about your fab and dial in good yields again; it's a whole 'nother thing to do that AND do it at the finest pitch yet.

Tim
That's why a lot of research into new semiconductor materials is based on growing them as a layer on silicon, where so many problems have already been solved.
 

Online David Hess

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #27 on: May 27, 2017, 07:11:50 pm »
If they go to a different semiconductor, I'm curious how much dev time and cost they're going to incur on that.

It's one thing to change everything about your fab and dial in good yields again; it's a whole 'nother thing to do that AND do it at the finest pitch yet.

Doing this would conflict with Moore's Law if the cost per transistor is higher and the way to avoid that is to place more transistors in a given area.  Some of the transistor performance in later process generation steps went *backwards* but what mattered was cost per transistor which required a density increase.  Density increases also require lower power per transistor which is what made that an overriding concern over performance in every later process generation; the performance may be worse but the power and density *must* be better.

What is being suggested with the use of a dense but exotic high performance process has been tried in the past and it always lost compared to denser silicon CMOS even when the later was lower performance.

Maybe things will change but is this same exotic process going to be used for the cache memory?  Because unless it is also denser, it is going to have to compete with processors built on silicon CMOS processes which cost the same or less but have many times more transistors available to build more complex out-of-order processors that can operate at higher frequencies despite the same cache memory latency.

To me that says Intel and the server processor manufacturers will be the first to take advantage of an exotic process because it is the only way they can get higher performance per core and they have customers who will pay for it.  ARM still has the option of relying on power and density scaling to make a more complex higher frequency processor and Intel does not because they already did that several process generations ago.
 

Offline Muxr

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #28 on: May 27, 2017, 07:32:41 pm »
Yeah. The latest crop of FinFet die shrinks didn't result in any money saving. The cost has gone up but it's at a break even point because of more die per wafer. The advantage in power consumption and f-max is the main advantage to going to FinFet, used to be you also got a cost saving by doing it.

The other thing that's getting really expensive is masks. It's is starting to cost exponentially more to tape out chips on these new processes. Each time the mask set for a new design pretty much doubles the previous one. For big complex chips we're already approaching a $100M territory. Just to tape out a chip. So unless you're a big manufacturer who sells these chips in millions it's not worth the cost.

This is actually a good thing for FPGAs. As more and more applications will find FPGAs to be the right balance between leveraging a new process and keeping the costs down. This in turn should lower the cost of FPGA. I am purely speculating though.
 

Online David Hess

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #29 on: May 27, 2017, 07:46:03 pm »
Yeah. The latest crop of FinFet die shrinks didn't result in any money saving. The cost has gone up but it's at a break even point because of more die per wafer. The advantage in power consumption and f-max is the main advantage to going to FinFet, used to be you also got a cost saving by doing it.

Which just says to me that Moore's Law already ended and the new law involves the number of transistors for a given power instead of price.

A couple months ago there was a great discussion in a video on this subject with graphs and numbers and everything from an older Intel fellow but I lost the link and have not been able to find it. :(  I do not remember it showing that Moore's Law had ended yet.

Update: just because I love you guys so much (ha!), I went back months in my Slashdot log of posts and managed to find a link to the video by Intel's William Holt, "Moore’s Law: A Path Forward".  The original video that I watched is at the Vimeo link but I hate Vimeo so I also found a YouTube link which may be the same thing but it is significantly longer and I have not watched both again for comparison:

https://player.vimeo.com/video/164169553

« Last Edit: May 27, 2017, 08:07:31 pm by David Hess »
 
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Offline coppice

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #30 on: May 27, 2017, 07:54:44 pm »
The other thing that's getting really expensive is masks. It's is starting to cost exponentially more to tape out chips on these new processes. Each time the mask set for a new design pretty much doubles the previous one. For big complex chips we're already approaching a $100M territory. Just to tape out a chip. So unless you're a big manufacturer who sells these chips in millions it's not worth the cost.
The corollary of that point is that if you won't be able to get a lot of saleable products out of a single die, the die will only be economically viable in a few niches, like DRAM, when the volume for a single saleable variant is huge. Look at a massive family of parts, like an MCU family, and there are unlikely to be more than a few dies involved. Test time operations enable or disable areas of memory, peripherals, etc. Future MCU families will push this further. Its much cheaper to waste most of the silicon, rather than create more optimised mask sets.
 

Offline Muxr

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #31 on: May 27, 2017, 07:57:58 pm »
Yeah. The latest crop of FinFet die shrinks didn't result in any money saving. The cost has gone up but it's at a break even point because of more die per wafer. The advantage in power consumption and f-max is the main advantage to going to FinFet, used to be you also got a cost saving by doing it.

Which just says to me that Moore's Law already ended and the new law involves the number of transistors for a given power instead of price.

A couple months ago there was a great discussion in a video on this subject with graphs and numbers and everything from an older Intel fellow but I lost the link and have not been able to find it. :(  I do not remember it showing that Moore's Law had ended yet.
Yup, it's dead as we know it. But it continues on a new journey. The important part is doubling of transistors each 18 months. Which is also getting increasingly harder to do, due to declining yields. Impurities and defects are a much bigger factor the smaller you go in terms of process pitch.

But there are ways around it. Companies are designing redundant features into the chips and designing them for harvesting/binning more and more, so they can be salvaged (with defective portions disabled).

Also packaging technologies to package multiple smaller dies in a same package. MCM packages have been around for awhile:


There is also really nifty die stacking going on. They use an interposer which is basically a silicon die built on a cheaper process like 32nm or similar, used to stack smaller die built on more expensive process on top.





 

Online David Hess

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #32 on: May 27, 2017, 08:15:06 pm »
Yup, it's dead as we know it. But it continues on a new journey. The important part is doubling of transistors each 18 months. Which is also getting increasingly harder to do, due to declining yields. Impurities and defects are a much bigger factor the smaller you go in terms of process pitch.

This is a great point which I should have made.  Moore's law does not care about *how* the cost per transistor is decreased.  Larger wafers and better yields also lower the cost per transistor.

See my updated post above for links to video of Intel's William Holt discussing the economics of Moore's Law.

The corollary of that point is that if you won't be able to get a lot of saleable products out of a single die, the die will only be economically viable in a few niches, like DRAM, when the volume for a single saleable variant is huge. Look at a massive family of parts, like an MCU family, and there are unlikely to be more than a few dies involved. Test time operations enable or disable areas of memory, peripherals, etc. Future MCU families will push this further. Its much cheaper to waste most of the silicon, rather than create more optimised mask sets.

I have made this point before comparing Intel and ARM in connection with ARM replacing x86.  Like the conflict between Intel's CISC and other RISC processor manufacturers in the past, Intel is not facing a single ARM juggernaut.  Instead they face lots of different ARM manufacturers who all have their own individual product designs.
 
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Offline timb

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #33 on: May 28, 2017, 12:40:54 am »
It's probably gonna cost them an ARM and a leg to get past it!

Badum-tss!

Working on the cutting edge can be quite RISCy, but eventually there will be a breakthrough that SPARCs a new CPU ARMs race. Only time will tell which company ends up the ALPHA dog.
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Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #34 on: May 28, 2017, 12:52:36 am »
It's probably gonna cost them an ARM and a leg to get past it!

Badum-tss!

Working on the cutting edge can be quite RISCy, but eventually there will be a breakthrough that SPARCs a new CPU ARMs race. Only time will tell which company ends up the ALPHA dog.

How did you get this INTEL? That's pretty EPIC tbh.
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Offline Mattjd

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #35 on: May 28, 2017, 01:08:24 am »
If I am remembering my electronics class correctly. A good deal of it has to do with being able to only decrease the size so small. If you look at the current equations of an nmos you'll some this constant K_n

K_n ultimately equals (U_n*C_ox / 2 )*(W / L) where

U_n is the electron mobility
C_ox is the capacitance of the oxide layer used to form the capacitor between gate and body (which can be decomposed further but is good enough for this explanation)

both C_ox and U_n are material dependent and are fixed for the most part.

W = width and

L = length

W/L is ultimately the ratio that is manipulated to change. The W and L are whats changed to increase the current. The problem is, we're getting to sizes so small that not many changes can be made anymore.

So this leaves us to having to manipulate C_ox and/or U_n. They could be changed, as there are materials other than Silicon that can used. The issue comes from manufacturing and companies refusal to change. There are limited facility that can actually print these processors, a lot of money would have to be invested to create them with new materials.
 

Online BrianHG

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #36 on: May 28, 2017, 01:36:32 am »
It's probably gonna cost them an ARM and a leg to get past it!

Badum-tss!

Working on the cutting edge can be quite RISCy, but eventually there will be a breakthrough that SPARCs a new CPU ARMs race. Only time will tell which company ends up the ALPHA dog.
How did you get this INTEL? That's pretty EPIC tbh.
Read these 2 articles:
https://www.extremetech.com/extreme/175727-ibm-builds-graphene-chip-thats-10000-times-faster-using-standard-cmos-processes
http://www.computerworld.com/article/2507086/computer-hardware/ibm-shows-smallest--fastest-graphene-processor.html

Now, I cant say for sure graphene is the future, but, it demonstrates that something new will come along improving silicon's speed performance in time as we are stuck in this current slowdown hump.  But yes, eventually physics will eventually put an end to it all as we one day get to the point where we can construct devices from the atom up...
« Last Edit: May 28, 2017, 01:50:10 am by BrianHG »
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Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #37 on: May 28, 2017, 01:51:54 am »
Who knows, maybe we can somehow build using electrons. Maybe we will start using subatomic quarks?

IMO once we hit the ultimate barrier of an Atom, it's going to become a game of who can bring the price down and the yield and efficiency up.
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Offline Red Squirrel

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #38 on: May 28, 2017, 02:20:21 am »
I think we will hit a point where we can only grow in parallel.  More cores/cpus and applications that need that power will just need to be designed to leverage multithreading so each thread can run on it's own core.
 
 

Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #39 on: May 28, 2017, 02:23:58 am »
That's my point. I think the game is going to become bringing the power consumption and heat down on more complicated dies.
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Offline james_s

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #40 on: May 28, 2017, 02:26:28 am »
I think we're already to that point, at least to some degree. It's not as if Moore's Law was ever an actual law of physics, it was just an observation of a trend, everyone knew it could not go on forever.
 
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Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #41 on: May 28, 2017, 02:28:13 am »
The theoretical limit is around 5nm according to Wikipedia, with some prototypes working.
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Offline SeanB

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #42 on: May 28, 2017, 09:47:37 am »
I would also add that current processors already operate at an energy density roughly equal to the surface of the sun, and the biggest issue is to cool this die and get the heat out evenly across the surface, but still have a good insulator to keep the leakage curent to the thermal solution well below what is going to slow the rise and fall times of the signals. Another issue is the speed of light, while the 5GHz might go 6cm in a cycle, it really is only going to be sampled on the rising edge ( or falling edge depending on the logic in the particular part of the die) and will also be only available on the other edge on the origination side. Thus, with C in silicon being a crap load slower than in a vacuum, you are limited to under 1cm of total trace length with polysilicon, and slightly more with a copper interconnect ( thus the IBM patents for copper on silicon interconnects that garnered them so much revenue over the years) so that you can actually have a reliable data transfer of data, and you need to have all traces matched lengthwise and all will be transmission lines with a defined impedance as well.

Thus you see things like clock generation and distribution having most of the silicon die space, and that there are more data lines snaking through than logic, along with doing things in stateless logic and clockless logic whenever possible so that you can shave a tiny bit of time off them, along with shutting off whole swathes of the die between instruction cycles so as to save power lost in the really leaky transistors in there.

Pretty much all at the limits of current processes, and adding extra cores and getting the programmers to make software that will use them as efficiently as possible is the way forward. Thus you see graphics cards with essentially 1000 Z80 processors on board, simple and small, but with very fast memory and really fast sharing of data between them, so that you can do a lot of things in parallel when you need to, so they are more capable than the individual processor core itself. Kind of like an ant nest, where each individual is small and seems unable to do much, but in a collective they are capable of doing massive tasks in a short time, without much coordination other than simple semaphores and limited data transfer.
 

Online T3sl4co1l

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #43 on: May 28, 2017, 10:25:37 am »
I would love to see "lossless" logic take a spin at ~nm scale.  While the density will be considerably lower (4x or worse I think?), and the clock speed reduced similarly, the power level would make practical to stack CPU dice.  Multicore designs could stack up rather than "around", interleaved with cache and whatnot as needed.

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Offline Terabyte2007

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #44 on: May 28, 2017, 11:30:36 am »
Typically 4-5 GHz is all you will see unless you're modding the PC with super cooling, water cooling, overclocking, etc. One of the possibilities is to build up or essentially 3D cores. These would be stacks of cores and by keeping the clock speeds reasonable your could gain effective speed advantages there. Heat will always be your battle with silicon until we move away from this substrate to something entirely different you probably won't see big leaps in processor technology when it comes to speeds. But luckily, I don't think this will be an issue for much longer.  ;)
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Offline brucehoult

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #45 on: May 28, 2017, 12:43:42 pm »
Just remember that the declared clock speed of a processor is the speed of the external clock only.   They routinely divide that clock a lot before it reaches the ALU.   Different parts of the CPU operate at sometimes vastly different clock speeds internally.

That was true in the 70s and early 80s. It hasn't been true since around the 80486/68040 era, and certainly not since anything Pentium/PowerPC. Except for the dog called Pentium 4, where they bumped the MHz for marketing reasons, but it wasn't really real.
 

Offline grumpydoc

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #46 on: May 28, 2017, 12:53:52 pm »
Just remember that the declared clock speed of a processor is the speed of the external clock only.   They routinely divide that clock a lot before it reaches the ALU.   Different parts of the CPU operate at sometimes vastly different clock speeds internally.

That was true in the 70s and early 80s. It hasn't been true since around the 80486/68040 era, and certainly not since anything Pentium/PowerPC. Except for the dog called Pentium 4, where they bumped the MHz for marketing reasons, but it wasn't really real.

Indeed clocks these days are multiplied up for internal use.
 

Offline brucehoult

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #47 on: May 28, 2017, 12:58:01 pm »
Just remember that the declared clock speed of a processor is the speed of the external clock only.   They routinely divide that clock a lot before it reaches the ALU.   Different parts of the CPU operate at sometimes vastly different clock speeds internally.

That was true in the 70s and early 80s. It hasn't been true since around the 80486/68040 era, and certainly not since anything Pentium/PowerPC. Except for the dog called Pentium 4, where they bumped the MHz for marketing reasons, but it wasn't really real.

Indeed clocks these days are multiplied up for internal use.

Well, yes, the external 100 MHz or 133 MHz or whatever clock is multiplied by 30 or 35 or 40 or 45 to get the internal (and advertised) clock speed, and it's even adjusted dynamically for power consumption, temperature, or load reasons.
 

Offline yada

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #48 on: May 28, 2017, 04:33:27 pm »
To add to David's and muxr's great responses:

If you want a high operating frequency, you need a small die so you can meet the timings. (Hint: signals travel at the speed of light at most, which becomes very noticeable at such clock frequencies; example: 5GHz=6cm wavelength, meaning a clock cycle's data can only travel 6cm before the next clock cycle begins)
If you increase the frequency, you increase the leakage and switching losses in the transistors, so smaller transistors generate more heat at the same frequency as bigger ones, causing issues with thermal management. (gate isolation is one of the issues)

I know we are getting to end of mores law as transistors approach the size of 10's of atoms, but why have clock speeds stopped at about 1.8 GHz and they just add more cores? Is it because of RF properties of the signals are causing too much loss? 1.8GHz doesn't seem that fast compared to the pace things have been progressing at.
I'm assuming you refer to CPUs used in mobile devices. As David pointed out, efficiency is an issue. I'd like to add to that and say that efficiency is an issue because of both the limited energy supply and the thermal management. Even if you had an unlimited power supply, the CPU ultimately warms the case (not a good heatsink) which you hold in your hand. There is no fan like in a desktop, so power dissipation has to be limited even when supplied with unlimited power, making efficiency paramount.
are you sure there is a 1:1 correlation in speed and wavelength? a 300MHz (1 meter wave length) signal will travel 6cm at the same speed as 6GHz. I think you are right for the wrong reasons.
 

Offline magetoo

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #49 on: May 30, 2017, 01:39:24 pm »
In addition to what's been said, another factor is that for desktop processors Intel has been the undisputed performance king for a long time with no real competition to speak of, and so has had little reason to waste money by trying to squeeze out more raw performance in their designs.  That might change now that AMD has a new generation of CPUs that can actually compete at the higher end.

And most of the peak computation load these days is probably done by GPUs anyway, not the CPU.
 


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