pci thunderbolt cards for pc - do they (only) use onboard graphics?
January 11, 2019 9:11 AM   Subscribe

Do pci thunderbolt cards for pc just use your pc's integrated graphics card? Or can a thunderbolt connected display utilize the gpu of whatever additional video card you may have purchased for your system?

Maybe the answer here should be obvious to me but it is not, since if it's the latter, then it's weird that you are using a display that is not physically connected to the card. Thanks mefiters. : )
posted by bitterkitten to Computers & Internet (10 answers total)
Thunderbolt is a mess of Intel weirdness, so I wouldn't expect anything except those specific use cases the manufacturer explicitly states works.

Which specific card are you thinking of? If you go spelunking on the egpu forums you might get some useful answers.
posted by pharm at 9:32 AM on January 11

Which exact brand and model is going to be used is not as important as some performance (heavy Photoshop and InDesign use). However, the situation is: got a bunch of macs with LED Cinema thunderbolt displays that all work fine. Getting new pc's, but seems a waste to just toss those Apple displays, since they still look great and were kinda expensive. Want to use the Apple displays with new pc's.
posted by bitterkitten at 9:47 AM on January 11

Thunderbolt is weird, but it's supposed to function as an extension port for the PCI/PCI-e bus, so it's possible. as long as the hardware is visible on that bus it should work. I'd give it a try at least.

we are using a Thunderbolt to ExpressCard adaptor for an off-label use with some new laptops at work, and it works just fine as far as we can tell.
posted by ArgentCorvid at 11:20 AM on January 11

I hadn't heard of these things before, but looking at this PCI card it appears that there's a DisplayPort input on the card itself that you're supposed to connect to the graphics card*. I assume it uses the motherboard's video chipset through the PCI bus if this isn't connected.

* (it sounds silly, but that's exactly how old Voodoo graphics cards worked, except with a tiny VGA cable)
posted by neckro23 at 11:59 AM on January 11

So I can say that Thunderbolt 3 is actually a multiplex of a USB bus, a PCIe bus, and a Displayport bus, and each of the busses in that multiplex are essentially independent. So there would be no reason to expect that if you hooked the Displayport input into a PCIe GPU it wouldn’t work, or that if you didn’t hook the Displayport input to anything there would be any display at all.
posted by doomsey at 12:06 PM on January 11

So, it looks like the thunderbolt cards on the market will take input from the PC graphics card & feed that to a monitor attached to the thunderbolt port.

But all the cards I can see on the market have /really/ specific restrictions on which motherboards they work with. In particular, I believe thunderbolt cards /only/ work with recent Intel CPUs / motherboards. You can’t just drop a thunderbolt card into a random PC and expect it to work - the bios has to support it & there has to be a header on the motherboard to connect the card to.

So buyer beware...
posted by pharm at 2:54 AM on January 12

On the other hand this post on the eGPU forums claims to have got the latest Titan Ridge based card working in an AMD PC, so maybe there is hope?

You could buy one & see if it works...
posted by pharm at 3:04 AM on January 12

I'd try hooking up your Thunderbolt monitors to the new PCs with whatever adapter is necessary (there should be some Thunderbolt to DisplayPort adapters out there, for instance). It'd help to know what specific model of monitor you have, and what sort of PC you're hooking it up to though.

The initial question is rather confusing and I think you're getting a lot of info assuming the use of eGPUs which isn't actually helpful to you based on your follow-up clarification.
posted by Aleyn at 11:26 AM on January 14

Also, to answer the initial question: unless you are hooking up the displays to the video card on a desktop system, it is unlikely that accelerated graphics will be piped through any on-board graphics system. Programs may still offload some processing to the GPU even in such cases, but I would expect better performance if you connect the monitor directly to the video card. (It's unclear to me if onboard graphics would even be capable of driving 4K displays at a full 60 Hz anyway.)
posted by Aleyn at 11:32 AM on January 14

Aleyn: Thunderbolt doesn't work like that: there are no “thunderbolt port on monitor” <> “display port on PC” adapters on the market that I’m aware of. There are adapters that go the other way, using “Alternate mode” to reallocate pins on a laptop thunderbolt output to be displayport pins instead, but those won’t connect a displayport output to a thunderbolt input on a monitor.

Feel free to prove me wrong though - there may be some product I’ve missed!

Also, my 2 generations behind the current release Dell laptop is perfectly capable of driving a 4K monitor at 60Hz using on-board graphics (no 2nd GPU on this thing, it’s an XPS 13"). I’m sat in front of said monitor right now & have just confirmed that the display is being driven at 60Hz, not 30Hz. You’re underestimating the power of modern hardware I think.
posted by pharm at 5:14 AM on January 15

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