Fiber-optic data transfer speeds hit a rapid 301 Tbps
livescience.com
livescience.com
As in, instead of just using fiber to make different computers talk to each other really fast, could we use it for like a RAM bus or something? Is there too much latency associated with it compared to the copper we've been using? 301 Tbps seems like insane speeds, even inside a computer.
https://www.tomshardware.com/news/intel-demoes-8-core-528-th...
Going from copper to optics and back again at the other end is significantly more expensive than using mechanical connectors. The complexity of optical fibers and their interconnects also adds a lot more assembly difficulty and failure opportunity.
We still have a lot of headroom in copper interconnects, but it’s getting more and more difficult to squeeze bandwidth out of longer distances interconnects like those between your CPU and your GPU slot. Next generation systems might need retimer chips at the halfway point to basically rebuild and retransmit the signal so it can make it the full distance. We also have to use more expensive PCB materials to reduce the cost. There may come a day when we have to connect the CPU and GPU optically, but it’s going to be a while before we get there.
We can beam billions of optical channels with different frequencies in parallel across chips, exabits (yettabits, yottabits) per second.
We will not compute with photons tough [4][5], the optical structures are to large and it would only work for very specific types of computations.
We design wafer scale integrations (very large chips) this way we can start making these fast on-chip interconnects around 2027 if we invest a few billion today in making free space optics. A layman's introduction in my talk here [3].
[1] Stanford Seminar - Saving energy and increasing density in information processing using photonics - David B. Miller https://www.youtube.com/watch?v=7hWWyuesmhs
[2] https://www.researchgate.net/profile/David-Miller-65/publica...
[3] Smalltalk and Self Hardware https://vimeo.com/731037615
[4] D. A. B. Miller, “Are optical transistors the logical next step?” Nature Photonics, vol. 4, pp. 3–5, 2010. https://www.researchgate.net/profile/David-Miller-65/publica...
[5] Attojoule Optoelectronics for Low-Energy Information Processing and Communications – a Tutorial Review https://arxiv.org/pdf/1609.05510.pdf
How much parallelization is required? Any idea how fast a single channel could get with optical transport and photon-detecting transistors?
As an Elixir dev (where parallelization is relatively easy), I think there is a lot of potential for parallelization that isn't being used by most programs, but for serial algorithms where multi-core can't be used, I wonder what the ceiling will be.
Terabits per second per channel would be possible but it would require to much high energy SerDes (serializer-deserialiser) circuits. It will be more energy efficient to have more parallel optical channels (bundled) switching at the low power optimal speed of the transistors, around 1-2 Ghz instead.
>I wonder what the parallelisation ceiling will be? How much parallelization is required?
There is no ceiling, no limit, for example look at an "existence proof": there are around a hundred trillion cells in your body that perform billions of computations chemically and also with DNA processing by ribosomes in parallel. No limit. Those 8 billion bodies theoretically could learn to work together with the aid of internet and personal computers. There are 10^24 stars in the universe.
Your thinking, your imagination, your thinking brain modelling of parallel systems is the ceiling, the limit. But you can learn, experiment and improve over time so your limits on thinking up better ways to parallelise computation will improve. Humanity could dedicate itself to the open ended creation of knowledge (of knowing how to compute in parallel with photons without limits) [1].
Right now our computation limits are limited by our knowledge (of manufacturing at atom scales), the energy output of the sun and the amount of atoms in the solar system we could rearrange [4]. We should fund our scientists to create the knowledge we need to enlarge the limits [5]. I hope you'll fund me as well :-)
> Elixir development
Smalltalk, LISP, Erlang, Elixer, Actor Language are some of the best message passing programming languages for massively scaling parallelism.
Alan Kay [2][3] has great lectures to get you started in thinking better (including about (computational) parallelism, scaling and message passing). A few others have written some papers as well (see links in my HN comments the last 12 weeks). I can teach you a bit too, write to morphle73 at gmail dot com.
[1] Chemical scum that dream of distant quasars https://www.ted.com/talks/david_deutsch_chemical_scum_that_d...
[2] Alan Kay lecture: putting Turing to work https://www.heidelberg-laureate-forum.org/video/lecture-putt...
[3] Is it really "Complex"? Or did we just make it "Complicated"? https://www.youtube.com/watch?v=ubaX1Smg6pY&t=2557s
[4] https://gwern.net/doc/ai/scaling/hardware/1999-bradbury-matr...
The practical ceiling will be set by manufacturing limitations for the next few decades: can we build structures atom by atom? [1]
[1] Richard Feynman "Tiny Machines" Nanotechnology Lecture - aka "There's Plenty of Room at the Bottom" https://www.youtube.com/watch?v=4eRCygdW--c&t=1390s
The biggest advantage of optical is less loss, which makes a huge difference for a long channel. By this I mean really long, like meters. Till that point it has literally no advantage while it is so much more complicated.
Ironically, the heat produced by the optical transceivers is one of the biggest problems.
I'd think optical will replace back-plane side but not anything within a motherboard itself in the coming 10 years. Copper has a lot of juice left in it.
I suppose a relatively high-speed chip-to-chip standard in use within consumer computers today is GDDR. If you want something with serdes then it's obviously PCIe, which has been using NRZ and now PAM4. Then there's Interlaken which has been around for yonks in HPC and networking. More recently NVLink also. None of these point-to-point serdes solutions can give you latency anywhere near DDR. And when they get to 200Gbps, copper backplanes are dead. It's cable now, and optical is coming. On the PCB, copper channels are thankfully holding out.
I would prefer to keep my clothes on, thanks.
(It's spelled "bear with me")
So nothing really new. I am still looking forward to 1 Pbps. And more undersea cable being built.
See this link for more info: https://www.nict.go.jp/en/press/2023/11/30-1.html
Although even the university article doesn't link the paper..
Most of the time it’s easier to just add another few dozen fibers when laying cables.
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e.g. speed of light could mean a ~40ms ping between LA and Sydney, but best we get today is probably around 150ms?
There are delays (very small) converting a signal from electrical on one end of the fiber to light and back to fiber on the other end. For this reason, DAC tends to have measurably lower latency compared to fiber for in-rack networking.
The length of an undersea cable is greater than both the straight line and the great circle distance between two points on the earth's surface.
These things do not explain all (probably not even most) of the difference between the latency you suggested and that in the real world, but I hope they help to suggest why the naïve calculation is not achievable.
Curious what you mean by “straight line”; Rhumb line?
Network hops are notoriously slow. In the datacenter the best I have ever seen is 200ns or so per packet which is very rare, most in DC hops are closer to 3-9 usec (especially modular chassis); then you hit the routers. With moderate congestion your routing hops are going to be twice that or more ignoring queuing, and you are likely six hops at least between two points in each direction.
The hollow core stuff mostly will jot help since it gains with distance, but distance means more hops on average, so we are talking about an application where low latency is required but distances are high (where the improvement applies) but the minimum latency achievable is still tens of ms.
It is interesting technology but I think it’s more interesting for hypothetical materials savings than for latency improvement.