51–60 of 108 posts
Earlier quoted context omitted.
Not sure how applicable it is, but the IrDA (Infrared Data Association) protocol tops out at only 16Mbps.
False. >GigaIR: 512 Mbit/s – 1 Gbit/s, NRZI, 2-ASK, 4-ASK, 8b/10b https://en.wikipedia.org/wiki/Infrared_Data_Association
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…
In this case, the pattern is:
1. Identify and refute common conception
2. Compare easily understood numbers
3. Assert basis of knowledge
4. Introduce a clear, tangible model for alternative thinking
5. Appropriate use of emotional resonance to capture and maintain attention
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…
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 c, if you're pulling a vacuum) means physical size doesn't matter as much. At 4Ghz you can move information 7.5cm in one cycle, and that's a pretty large distance compared to any integrated circuit I've ever seen.
Why is storage necessary? If you can move bits to optical gates and get a result back it seems to me like you can work around the fact that, in an electrical system, capacitance and heat (due to density achieved in the quest for minimizing capacitance) start to limit the computation you can do.
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…
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?
Transmission time isn’t really the main issue, it’s more about the work required to get a memory request through the levels of the hierarchy to DRAM and back. Probing each level of cache, propagating through the miss queues, translation (maybe with TLB miss), waiting for the DRAM controller, etc.
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 fast! And you can't skip the TLB, even if you don't have any data caches.
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?
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.
Earlier quoted context omitted.
Transmission time isn’t really the main issue, it’s more about the work required to get a memory request through the levels of the hierarchy to DRAM and back. Probing each level of cache, propagating through the miss queues, translation (maybe with TLB miss), waiting for the DRAM controller, etc.
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…
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…
Have you ever tried wiring any non-trivial logic without flip-flops? Say, a simple signal routing layer. Even the most basic bits of logic becomes much less efficient to downright impossible without storage.