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Optical PCIe 7.0 connection hits 128 GT/s

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204 points WithinReason | 2 comments | 17 Jun 24 11:42 UTC | HN request time: 0.021s | source
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yjftsjthsd-h ◴[18 Jun 24 00:02 UTC] No.40712649[source]▶
So I guess what this makes me wonder is: Why are we using electrical signals to connect the data lanes between components and computers these days, rather than moving everything to optical for data movement (obviously power would stay electrical, but that's already on separate lines)? I assume there's an element of cost, and once the photons get where they're going they have to be turned back into electrical signals to actually be used until such time as we get around to getting pure light based computers working (someday but not yet...), but that must not overwhelm the advantages or we wouldn't be looking at this being developed.
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1. Aurornis ◴[18 Jun 24 12:50 UTC] No.40717224[source]▶
> I assume there's an element of cost,

This assumption is very correct. Optical interconnects are extraordinarily expensive relative to copper. We have the art of manufacturing copper PCBs and connectors mastered. Putting optical interconnects into a system requires that the signal go through transceivers at either end as well as external optical cables, which are not integrated into the PCB. It’s extra components and complexity everywhere.

The reason optical interconnects are being explored here is that next gen PCIe is so extremely fast that the signals cannot travel very far in PCBs without significant losses. PCBs built for these speeds require special, expensive materials on the layers with those signals. They might require retimer chips to amplify the signal past a certain distance. These limitations may not apply to consumer motherboards with a single GPU very near to the CPU, but datacenter motherboards might need to connect many GPUs across a large chassis. The distances involved could require multiple retimer chips along the way and very expensive PCBs. Going to optical interconnects could introduce much more flexibility into where the GPUs or other add in cards are located.

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2. chx ◴[18 Jun 24 13:04 UTC] No.40717367[source]▶
As a side note: while the O in OCuLink does stand for optical that variant is not in use. Every OCuLink connector and cable are just ordinary copper interconnection.

Meanwhile Samtec has PCIe active optical cables, they have had them since 2012, it's a very niche application currently.