- Posts: 175
- Joined: Sat Aug 03, 2019 1:48 am
- Location: Perth, Australia
- Real Name: Steven Graham
I'll give it my best try (I'm not an expert on hardware architecture but I think I understand it enough).
So think of PCI lanes as data pipelines that can function both individually or together for data to be streamed through. Regardless of the bandwidth max (determined by the various generations of PCI, like PCI 1.0, 2.0, 3.0 (what you have) and 4.0 (the latest gen), multiple lanes act as multipliers if a specific device needs that much more data.
The biggest PCI lane hogs are GPU's, so that 2070 Super can suck up to 16 lanes if it wants to. It typically doesn't need to and you'd never know the difference if it was only utilizing 8 lanes.
To further complicate things, PCI lanes can be provided by both the CPU and MotherBoard. Typically CPU lanes are used for GPU's, while Motherboard lanes are used for nVME drives and some minor PCI slots like those 1X and 4X.
As more lanes are used by GPU's, the number gets divided, so for instance a single 2070 can be placed in the top PCI slot and utilize 16X speeds (as I mentioned, overkill in most situations), however if you add a second GPU, then they would both max out at 8X. Add a third GPU and you might be down to 4X for each card (which might slow down the GPU's for some operations, but is still plenty fast for most).
In your particular case, I wouldn't worry about it. You have a single GPU and a single nVME drive (likely using your motherboard PCI lanes), so adding that Thunderbolt card will still keep you with plenty of speed, and even if your GPU might go down to 8X from 16X, you'll never notice it in Resolve.
As a matter of fact, I would even say that you have room to expand and add a second GPU, and even a second nVME drive (if your motherboard has a slot for it) without Resolve taking any performance hits.
In the future, if you decide to build a new workstation and are concerned about running out of PCI lanes, you might consider switching to either the higher end Intel CPU's like the 10980XE or XEON line, or alternatively switch to AMD Threadrippers which support considerably more PCI lanes and in the AMD case even support the latest PCI 4.0 generation which is even faster (hence requiring less lanes per card).