71–80 of 108 posts
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Wouldn't infrared be acceptable for data transmission?
Not sure how applicable it is, but the IrDA (Infrared Data Association) protocol tops out at only 16Mbps.
IrDA has its uses but it seems they don't deal with fiber comms.
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What? That doesn't make sense. If cache probing would be the cause for DRAM accesses being slow, we wouldn't need caches. We would just access DRAM directly! It's the other way around: DRAM accesses are slow, that's why we need caches. > translation (maybe with TLB miss) In most architectures, the caches are physically addressed, so TLB lookups occur before even L1 cache access. Successful TLB lookups are extremely f…
> In most architectures, the caches are physically addressed, so TLB lookups occur before even L1 cache access. So to see if a memory location is contained in a cache line, a TLB lookup is needed to first get the physical address? I wouldn't have expected this, can you expand on why this is the case?
Gaaah, please stop advertising optical computers as the technology that will overcome Moore's law. It makes no effing sense. Wavelength of the light emitted by these devices: ~4000nm Latest generation commodity CPU transistor structure size: 7nm Add to that that photons really don't like being trapped; you essentially need a delay line and optical amplifier to hold them indefinitely (that's essentially the core techn…
It's definitely not a continuation of Moore's law as it has nothing to do with transistor density, but it may mean that the performance people expect from computers - which is why people are usually talking about Moore's law - may continue increasing. I don't see how the wavelength is comparable to transistor size because as you switch to the optical realm, the benefit of information propagation at speeds near c (or…
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Photonic can only be up to 20% faster... And I'm talking about a fully photonic cpu, not an hybrid one that has a light/electricity translation cost.
> Photonic can only be up to 20% faster... How did you come up with that number? The speed of travel? That's not really the main bottleneck in current computer architectures, at least not yet. Using photons would enable quite different architectures that we haven't even conceived of yet.
At least I could find back However, optoelectronic devices lose 30% of their energy converting electronic energy into photons and back; this conversion also slows the transmission of messages. All-optical computers eliminate the need for optical-electrical-optical (OEO) conversions, thus lessening the need for electrical power.
So maybe that this number is wrong but has the research really been too mediocre to calculate the real maximum potential speed gain from light alone (and not new way of computing)? Or did they calculate it and decided to not make it visible online because otherwise they would loose funding?
Is the breakthrough here about emission or transmission? Or is the physics for these two connected? It's not clear to me, between the title and the article. Secondly, could using a "photonic" memory bus bring RAM access speeds close to cache speeds, or is the transmission distance/time not the main issue there?
> Secondly, could using a "photonic" memory bus bring RAM access speeds close to cache speeds [...] No, it really can't. The distance between CPU core and DRAM chips is approximately 10 cm, so at a typical electrical propagation speed of around 2/3 c, the round-trip time is 1 ns. A full DRAM access, however, is on the order of 100 ns. So physical transmission speed only accounts for about 1% of DRAM access times.
On top of that is power requirements which are again orders of magnitude higher than on chip signals.
Optical has a chance to fix that for the same reasons it works so well for longer distance networking.
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I thought electric charge in conductors already moved very close to C? https://en.wikipedia.org/wiki/Speed_of_electricity
Only if you consider 70% or so to be close. There's some room for improvement over copper wires. Now, if there are any physicists here who want to jump in, I have a question about that. I heard waveguides are dispersive, would sending pulses of light through tiny channels slow it down as well?
Unfortunately something like 0.7c is about the fastest speed of EM wave propagation in an optical waveguide or along a copper waveguide. Another comment here gives a slightly faster example with n=1.3, which is maybe achievable in some kind of polymer. Or in highly purified water, for what it's worth.
You can get a mild speedup, 40% or something, by moving to free space. But that is an unbelievable can of worms, taking all the signals out of the waveguides and somehow still getting 1B signals going to the right place. The 40% speedup doesn't remotely pay for giving up solid state waveguides.
"Dispersive" fortunately doesn't mean a meaningful slowdown. It just means that a transmitted bit will travel at a range of slightly different speeds. If it goes very far, the shape of the pulse will get messed up. But that's a problem people are already pretty good at solving.
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Wouldn't infrared be acceptable for data transmission?
Not sure how applicable it is, but the IrDA (Infrared Data Association) protocol tops out at only 16Mbps.
40Gbps per wavelength, not per fiber. Many times 40Gbps over one fiber.
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Is that a USA/North America thing, based on calling radio sets "transistor radios"? Here in the UK we had "the wireless", and I'm confident that my parents - late 70s - who were the generation of first domestic computer ownership in the UK would associate "transistor" primarily with computers.
Definitely not just a USA thing, "transistor" also meant "transistor radio" in Russian back in the day. (E.g. this song from 1982: https://learnsongs.ru/song/dinamik-na-plyazhe-pleshchet-voln... )
Gaaah, please stop advertising optical computers as the technology that will overcome Moore's law. It makes no effing sense. Wavelength of the light emitted by these devices: ~4000nm Latest generation commodity CPU transistor structure size: 7nm Add to that that photons really don't like being trapped; you essentially need a delay line and optical amplifier to hold them indefinitely (that's essentially the core techn…
Would be much appreciated.
Imagine a 3D printer at atom scale. But because the scale is so small, the nozzle has to deposit a gas.
The magic is in making the individual gas molecules get to the right place.
Layer by layer, to what theory predicted would be a light emitting configuration.
Incredible achievement.