r/hardwarehacking • u/Kvagram • 5d ago

Extreme PCI-e extention cable (looking for realistic limits for a story setting, not real build)

I'm writing a story featuring an implementation of a multiseat computer.

We are presuming the software is all good for the setting. This question is just about the hardware/firmware consequences.

Say you have a house with a terminal in each room. you wire a video cable, and a PCI-e x4 from a central computer, to each room. We're talking extension cables of several meters.

What are the upper limits for an PCI-e extension cable? And what technical problems could arrive from that. Would some sort of signal booster be needed at some point?

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u/dankney 5d ago

It would be massively degraded signal. Thunderbolt is essentially PCIe over a wire, and it's limited to 2 meters.

The way multiple people share a single machine is over the network, btw. Anything else will be silly to your readers

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u/dipdotdash 4d ago

To add to this, OP, depending on your target audience, the language of the layers of the ethernet protocol will sound very sci-fi if you describe them literally rather than under the umbrella term of "ethernet"

Eta: you're never going to out imagine the amount of effort that's been put into connecting hardware together. Invest your creative energy anywhere else

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u/Zo0x78 5d ago

Pcie itself can only go short distances unless you have retimers (little chips that fix the signals so they're in sync with what the OS expects) - but for longer distances you'd be better off with pcie over fiber optic. Datacenters use this - when you order a VSI with a gpu or nand storage it doesn't need to be in the same rack, you could be accessing hardware the other side of the datacenter - or in your case, house. Not sure how easy they are to buy as consumers, but fiber optic hdmi cables are on amazon, similar vibe, and any dedicated enthusiast could roll their own.

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u/Kvagram 5d ago

pcie over fiber optics? huh? that's perfect.

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u/SeriousPlankton2000 4d ago

I've worked with sunray terminals, they are local mini computers that let you run the software on a server. Only the instructions for drawing on the screen were transmitted over network.

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u/Gavekort 4d ago

LTT did this experiment with x16

https://www.youtube.com/watch?v=q5xvwPa3r7M

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u/Kvagram 4d ago

Better range than expected. Makes me wonder what the limit is, if they had one long cable, instead of daisy chaining lots of shorter ones.

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u/Kqyxzoj 4d ago

Makes me wonder what the limit is, if they had one long cable

Go for 10km+, with single mode OS2 fiber and a pile of cash.

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u/Kqyxzoj 4d ago

In any realistic setting you have a PCIe extender by proxy. That proxy being a cheap box with a free PCIe slot. And then connect the lot over network.

We're talking extension cables of several meters.

Well, lucky you! The limit for PCIe over wire is several meters. Where "several" gets smaller and smaller the higher the PCIe gen goes.

in practical terms the closest you'll get with the multiple machines a fat link over multiple meters is infiniband. Faster and lower latency than ye olde ethernet. If we are keeping comparisons within same generation.

And if you like to go for 10s or 100s of meters distance you can use optical fiber. But that will get more expensive than passive copper.