Author Topic: Why have CPU's stopped at ~1.8 GHz?  (Read 15034 times)

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Offline yada

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Why have CPU's stopped at ~1.8 GHz?
« on: May 26, 2017, 10:12:00 pm »
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.
 

Offline BradC

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #1 on: May 26, 2017, 10:16:32 pm »
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.

You might be a decade or so behind. CPUs have been able to hit a qualified 5GHz for a while now.
 

Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #2 on: May 26, 2017, 10:22:15 pm »
My i7-4790k runs at 4.4Ghz, and it's several years old
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Online james_s

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #3 on: May 26, 2017, 10:58:07 pm »
Mine is 3.5GHz IIRC. Speeds have hit a plateau though and now the trend has been to add more cores and do other refinements. There are physical laws that we are really starting to run up against. Moore's law cannot go on forever. Fortunately computers are already more than powerful enough for most uses, it's not like 20-30 years ago where a 1 year old computer was hopelessly obsolete and wouldn't even run current software.
 

Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #4 on: May 26, 2017, 11:14:08 pm »
Who knows. Intel has already said their 7nm chips are going on something other than Silicon. Maybe we will see a Moore's law revival?
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Offline Vgkid

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #5 on: May 26, 2017, 11:17:28 pm »
The laptop I was using last year ran at 1.8Ghz, it was perfectly useable. Ran Vista as well.
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Online james_s

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #6 on: May 27, 2017, 12:02:49 am »
Who knows. Intel has already said their 7nm chips are going on something other than Silicon. Maybe we will see a Moore's law revival?

For how long?

7nm is approaching the physical limit based on the size of the atoms, they simply can't go much smaller, at least not without a whole new paradigm.
 

Offline yada

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #7 on: May 27, 2017, 12:52:54 am »
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.

You might be a decade or so behind. CPUs have been able to hit a qualified 5GHz for a while now.

So pretend I said 5 GHz, why have things stopped at 5 GHz? Why add another core instead of making it faster like we have for the last 30 years? To me adding more cores seems to make more sense, but people tend to buy based on a bigger number. Look at cordless phones: 49MHz then 900 MHz then 2.4GHz then 5.8GHz even though 900 MHz has the best range through walls and buildings since you are just sending voice, which doesn't need much band width.
 

Offline Halcyon

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #8 on: May 27, 2017, 01:01:14 am »
Why add another core instead of making it faster like we have for the last 30 years? To me adding more cores seems to make more sense, but people tend to buy based on a bigger number.

As has already been discussed, we're reaching the limit on what can be done with current technology and manufacturing processes.

But simply adding more cores doesn't necessarily make applications run faster -- It depends on the application. It's still not uncommon to see applications which only run on a single core (or support less than the number of available cores in the system).
 

Offline technix

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #9 on: May 27, 2017, 01:01:25 am »
The overclocking world record was 7GHz on LN2, and it is reported that i3-7350K can often run at 5GHz or above. Hell I have even dialed in a small overclock for my Xeon E3-1231v3 (3.5/3.9GHz instead of 3.4/3.8GHz)
 

Offline David Hess

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #10 on: May 27, 2017, 01:26:40 am »
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.

It is a matter of power, efficiency, and memory latency.

Portable devices have a power envelope which limits the CPU to a less complex but more power efficient design which requires lower memory latency (1) and that limits clock speed.  The extra complexity of a desktop processor allows it to tolerate higher memory latency allowing a higher clock speed and greater performance but at a cost of lower efficiency.

A design made to take advantage of lower latency lower clock frequency memory cannot scale up to higher frequencies simply because it will spend all of its time waiting for results from memory.

(1) The core design is intimately linked with the load-to-use latency of the level 1 cache memory.  Low frequency cores might have a load-to-use latency of 2 or 3 clock cycles but high performance processors can tolerate 4 cycles of load-to-use latency.
 

Offline yada

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #11 on: May 27, 2017, 01:47:39 am »
So some part of it is that the memory can't keep up with the CPU? Also as far as desk tops are concerned, if you can't get the transistors any smaller why not go to a bigger die size, stack them on top of one another, or even make the circuit 3 dimensions? Go from the size of a postage stamp to four postage stamps? I realize its not this simple but my question is why?  We started out on a quest to make things smaller way before we knew it would have to fit into a smart phone. More cores doesn't solve the problems that are linear; where the next set of instructions depends on the last.
 

Offline BrianHG

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #12 on: May 27, 2017, 02:11:25 am »
DDR5 has passed 7GHz speeds already.

As for complex devices like CPUs, the next big speed hike after 7nm process will be graphene based transistors expected to be at least 20x faster.  Yes we are talking about 100GHz processors.
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Offline technix

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #13 on: May 27, 2017, 02:18:06 am »
This requires through-silicon via technology to be ready. Current we already have TSV-linked NAND and NOR stacks, but for processor cores nobody is doing it yet. Thermals may be the main problem here as all dies get very hot at the same time.
 

Offline Housedad

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #14 on: May 27, 2017, 02:27:01 am »
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.
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Offline David Hess

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #15 on: May 27, 2017, 02:27:19 am »
So some part of it is that the memory can't keep up with the CPU?

The level 1 cache cannot even keep up with the CPU.  The big advantage of a complex out-of-order processor is that it can deliver higher performance for a given amount of level 1 cache latency and that applies to a lessor extent to the upper cache levels and memory as well.  A complex out-of-order core can take advantage of greater memory parallelism than a simpler core and memory parallelism limits performance.

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Also as far as desk tops are concerned, if you can't get the transistors any smaller why not go to a bigger die size, stack them on top of one another, or even make the circuit 3 dimensions? Go from the size of a postage stamp to four postage stamps? I realize its not this simple but my question is why?

Desktops and servers *do* use larger dies.  The highest performance processors use the maximum die size available if only to have as much integrated cache memory as possible.

Power density prevents stacking high performance logic.  For the past few generations, high performance processors have been limited by how much power can be removed from the die so as the die has shrunk, the power *had* to be reduced.  On Intel's recent designs, the processors have to operate at a lower clock rate when power hungry features like 256 bit vector instructions are used to prevent areas of the die from becoming too hot.

If you check the highest performance grades for Intel desktop processors going back several generations, they all have a roughly constant power for a given die area.

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We started out on a quest to make things smaller way before we knew it would have to fit into a smart phone.

That is just economics.  Moore's law is about lowering the cost of transistors which means placing more transistors in a given area.

Quote
More cores doesn't solve the problems that are linear; where the next set of instructions depends on the last.

That is called Amdahl's law and it is why more higher efficiency but lower performance processors are not a replacement for higher performance but lower efficiency cores.
 

Offline Nusa

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #16 on: May 27, 2017, 02:51:40 am »
Measuring the systems actual performance is better than using the clock speed as a measuring stick.

But if you insist, here's the current records: http://valid.x86.fr/records.html
 

Offline Muxr

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #17 on: May 27, 2017, 03:40:11 am »
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.
As others have mentioned today's high performance CPUs run well into the 4Ghz+ (on laptops they are clocked more conservatively to save power).

But you seem to have a bit of a misconception about equating frequency to performance. Frequency is only a part of the equation. There is also something called IPC.. or Instructions Per Clock.

Modern CPUs are capable of executing more than one instruction at a time.. they accomplish this via tricks like out of order execution and superscalar instruction level parallelism. For instance a modern Ryzen CPU can technically work on executing 6 instructions at once. In practice however it is hard to keep all 6 execution units per core busy, because this requires ideal branch predictors and a particular mix of instructions.

Pentium 4 from 2003 could hit 4Ghz back then, but it was way slower than today's CPUs which run at 4Ghz. Because it had weak IPC among other things.

Also it is important to know how we got to 4Ghz in the first place. A monolithic execution pipeline where all the work is being done at once could not run at 4Ghz.. because you could never meet the timings. By the time the signal reaches the farther parts of the execution unit the execution window would be over and the new cycle would need to start before the work was completed, causing a crash. Such CPU would at best be confined to a few hundred Mhz. Yes process improvements usually called "die shrinks" do increase the f-max (frequency) ceiling, but that's only a portion of the story of how we got to 4-5Ghz CPUs.

Clever CPU designers came up with a way to reach even higher clocks. They split up the work in pipeline stages, where each stage does only a portion of the work.. and the work gets propagated to the next stage like a conveyor belt on each cycle. This allows each stage to be much smaller and therefore timings much easier to meet, allowing for high clocks 4Ghz +. For example Ryzen has a 19 stage pipeline (Intel's recent CPUs have 16).

The problem with this long pipeline approach is that every time you have a branch prediction miss.. the entire pipeline has to be evacuated.. because the instruction the CPU was executing was not to be executed yet, the CPU was executing the instruction under the assumption that it's the next in line to be executed but because it isn't it's the result is invalid, because the data the instruction operates on may have to be modified by another instruction, so for a 19 stage pipeline for instance this is 19 cycles wasted. This is where a good branch predictor is paramount. And in case of Ryzen AMD employs some neural net technology, the perceptron to improve branch prediction and keep branch prediction misses at a minimum.

So yes Moore's law is slowing down. A die shrink may give you 10-20% more frequency or it might not.. adding clever features can also improve performance, widening the CPU cores by adding more execution units for instruction level parallelism and other tricks can improve performance as well.. but at the end of the day it's all a matter of balance and power consumption budget, silicon budgets etc..

Leveraging parallelism is the best way to improve performance in applications when possible, because 6 and 8 core CPUs are becoming mainstream. And adding more cores is much easier than improving IPC or Frequency.
 
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Offline cdev

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #18 on: May 27, 2017, 03:43:08 am »
I've never really pursued overclocking because I'm afraid my system would become unstable, but I was able to get my computer to boot at well over 5 GHz without any modification whatsoever just by changing the multiplier.. I am using a fairly generic multicore AMD system thats normally clocked at 3.5-4 GHz. I leave it at its defaults because I like my PC to run whisper quiet.
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Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #19 on: May 27, 2017, 04:33:45 am »
Overclocking is primarily a game of heat management. Stability isn't something that is going to affect you in the long term really. If it runs stable for a week, it should be fine. Tweaking voltage helps with some stability issues.

A few things about overclocking:

Non-binned CPUs are normally better. If you can identify one of those, they tend to live a longer, more stable life.

Intel CPUs really need the K suffix to be truly overclockable.

There is a limit. It's not a case of "If I pump enough cooling into it, I can throw it to a billion Ghz". There will be a point where the CPU just won't run stable, no matter how much power and cooling you pump into it.

It will void your warranty unconditionally. Even if they market it as "Overclocker friendly", it's still gonna void the shit out of your warranty.

It will decrease the lifespan of your CPU. The extent depends on your level of overclock. It's not gonna be like from a 20 year lifespan to 4. It's more like if you run it 24/7 at a good overclock, a number somewhere along the line will decrease.

Do it if you need too. For me overclocking is a case of I either have tons of money to piss away (I wish I had this problem) or a case of future-proofing. I suggest you get a good system ready for overclocking, and wait until you come to a point where you can't do what you want to do on your machine anymore with your current CPU. At that point, overclock. It's not a game of just gonna throw the specs up a bit, no biggie. Regardless of what people say there are consequences. You are literally operating your machine outside of it's designed specifications, even if it's designed to go out of those specifications.

If you have a stock cooler that came with your CPU, forget about it. If you have an air cooler, be very careful and monitor temps like you would monitor your family in a bad Detroit neighborhood. While having an unstable OC is usually reversible, a 110c OC is not usually reversible. The rule of thumb is never go over 80 @ full load for extended periods of time. Spikes to 90c are alright, but go past that and you are living on the edge. 100c is normally the danger zone for good Intel CPUs, and if you see 100c on your silicon, cut the power, and cut your OC. Modern CPUs aren't as dangerous to overheat as older ones. It used to be that if you were to pump the multiplier too high, you would pop your CPU, but today you can normally be safe with throttling and emergency cutoffs. It's still never a thing to rely on.

Ask people. If you're unsure about OC, and experimental and strange computer configurations in general, ask people. Waiting a day to get a second opinion can mean the difference between busted box and busting box. Nobody is an expert here, not even the people who made the chips. By overclocking you are cementing your feet firmly into hobbyist territory, and we hobbyists almost always ask other hobbyists. It's just the smart thing to do. Follow common sense rules, don't make impatient actions, if it's too good to be true then it is, don't act like you know everything.

I have never overclocked anything in my entire life. All I have done is gather information for the day that I say I am too far behind, I need to put the hammer down, and give my chip a bit of a boost.

To answer the OP's question in my own words, the higher you go on the clock speed, the higher you go on the power and heat. You can see this through the evolution of PC power consumption and cooling. Up until the DX4 line of 486 chips, CPUs were rated for no-heatsink operation. You went from smaller, 8-10 fin heatsinks with a small fan on Socket 3 and 4 machines, to slightly beefier coolers on Socket 5, 7, and 8, and when the line got to Slot 1 and Socket 370, you started to see block coolers, with later sockets like the first Intel LGA sockets and AM2 having larger and larger coolers.

Today AMD has sold chips that require water cooling because with their limited architecture (Before Zen) they had to kick the speed up to stay even remotely relevant. This is where you get the old joke "AMD CPUs are space heaters"

Of course transistors have gotten smaller and more efficient, but the higher you go on clock speed the higher you go on heat and power. With more cores it's somewhat different. Of course it's more heat and power, but not to the extent of clocking higher. This is why most of the Xeon chips have loads and loads of cores at slower clock speeds with fairly moderate TDPs, all on air cooling.

Nobody knows what is going to happen. You can theorize all day, but at the end of said day, there will always be another person, back in history, saying a very similar thing, to be proven wrong later. People for the past thousand years have been making these predictions, and each and every one of them are wrong today. I am willing to believe history in that respect will repeat itself, but I too can be proven wrong (It's quite annoying actually). There may be new transistor tech, there may be new architecture tech. We may fundamentally re-envision the entire concept of computing at it's very core, but nobody knows as for yet.

My personal opinion is that there will be a way around. There always has. Stopping at a wall just gives time for people to work around it.

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Offline abraxa

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #20 on: May 27, 2017, 07:06:31 am »
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.
 
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Offline Syntax_Error

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #21 on: May 27, 2017, 03:28:50 pm »
Watch this presentation.



In a nutshell: They're working on it. A lot of people are working hard on it, but all the low hanging fruit is gone. Economics is more of a constraint than physics. Physics ultimately will be the final constraint, but we aren't there quite yet. But economics is making even the incremental gains slow down.
It's perfectly acceptable to not know something in the short term. To continue to not know over the long term is just laziness.
 

Offline Ampera

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #22 on: May 27, 2017, 03:32:17 pm »
It's probably gonna cost them an ARM and a leg to get past it!

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Online coppice

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #23 on: May 27, 2017, 03:56:01 pm »
Economics is more of a constraint than physics. Physics ultimately will be the final constraint, but we aren't there quite yet. But economics is making even the incremental gains slow down.
Economics will always be the final constraint. The current state is high value things can use quite expensive processes (e.g. III/V), but most things have to make use of something lower cost (e.g volume CMOS). That won't change. Even the high value applications will never be of high enough value to push things as far as physics will allow.
 

Online coppice

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Re: Why have CPU's stopped at ~1.8 GHz?
« Reply #24 on: May 27, 2017, 03:57:46 pm »
It's probably gonna cost them an ARM and a leg to get past it!
Chips with legs are really old fashioned. If you want to push device technology as far as it can go, its usually just an ARMs race.
 


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