modern high-end video cards provide a maximum of 4 display outputs, with each supporting resolutions in excess of 5120x1440. in total this is plenty of pixels, but for productivity I find many smaller displays to be more useful than fewer huge ones, and these huge displays are still very expensive. 15" 1920x1080 displays from dead laptops are free, used 2560x1080 ultrawide displays cost £60, and I contend that an array of these is a preferable solution to one or two 3840x2160 displays for productivity purposes (especially given how questionable Windows 10's windows tiling features are). the issue I am trying to address here is the shortage of display connectors for users wishing to connect more than 4 monitors to a desktop computer.
a second video card is an obvious solution to this problem, but there are some things to consider. in the case of GeForce cards, the primary and secondary video cards must be from the same generation* as two different GeForce drivers cannot co-exist. assuming the primary video card is modern, this means the secondary card must also be modern and thus will cost more than is strictly necessary for simply driving displays with 2D desktop workloads; this task can comfortably be handled by e-waste video cards from 5 generations ago and tying up even a low-end current-generation card with it feels wasteful.
*cards from adjacent, or even adjacent-but-one generations can work if they both support the same driver version, but updates are liable to break setups like this as support for the older card wanes.
the second thing to consider is PCI-Express lane allocation. on mainstream desktop platforms (X370, X470, X570, B350, B450, B550 for AMD CPUs and their Intel socket counterparts) there are not enough PCIe lanes to allocate a full 16-wide link to two video cards at the same time, so motherboards compromise. in my case, the topmost full-length PCIe slot runs in 16-lane mode only when the lower full-length slot is not occupied, and drops to 8-lanes when the lower slot is occupied (giving the other 8 to that slot). assuming the primary card is a high-performance one, and especially if the PCIe generation is an older one (3.0 in my case), losing these 8 lanes for the primary card is not ideal for performance. in my rudimentary testing this was significant, and some proper testing by techpowerup finds similarly. all ATX and mATX motherboards will provide other PCIe slots where population does not nerf the primary x16 slot, but mostly these are not full length and thus will not accomodate a video card without modification.
PCI-Express (electrically) supports devices at any link width lower than the maximum supported one, so an x16 video card will in principle work fine in an x8, x4, or even x1 slot assuming it can be physically hooked up*. bandwidth will be reduced, but for low-stress applications like desktop rendering this will not be a problem in practice. my goal here was to find a suitable (very cheap, low power, providing at least 2 additional display connectors) video card and run it at a lower link width in one of my motherboard's shorter PCIe slots. this will require modifying either the slot on the motherboard (opening the end of the slot) or the card (removing the section of the connector not accomodated by the target slot). while the former strategy is less destrucive, it requires that the motherboard has no components higher than the base of the PCIe slot placed in the area beyond the end of the slot. it also requires more disassembly, and surgery on the motherboard which is in my case mission critical. for this reason I prefer to modify the card.
*the data link will scale down gracefully, but the power supply may not. some cards require use of the full 75w max power delivery from the x16 slot for instance, and may not work properly with only the 10w maximum provided by an x1 slot.
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using a stanley knife with carbide blades it's possible to easily notch the slot connector where you plan to cut, then cut with a bimetal hacksaw blade. take care to cut only as deep as is required and not to sever any traces which look integral to the circuitry on the bracket side of the cut. this feels unpleasant, but remembering that the victim is a used and obsolete card procured for £10 is helpful. also important is scraping any mangled traces at the bottom of the cut until you feel sure there are no shorts between PCB layers. with this done, the NVS 310 I chose fits nicely into the topmost x1 slot on my motherboard and outputs correctly on the two DisplayPorts it provides.
unfortunately, not only do different GeForce driver versions not coexist on Windows, but none of the GeForce drivers will coexist with the Quadro/Tesla NVS series driver. even after preventing Windows Update from automatically installing this Quadro driver* and manually applying the Microsoft generic display adapter driver, I could not make this card output properly while maintaining funcionality on the primary GeForce card.
*for a while Microsoft provided this excellent GUI tool for manually omitting individual hardware devices from having their driver affected by Windows Update. when messing around with off-label uses for older cards, this is absolutely invaluable and as far as I can tell they do not provide this tool any more. as of 2024-01-14 it still works perfectly on Windows 10 LTSC - your mileage may vary but I will leave it here in case anyone finds it helpful.
for another £10 I picked up an ATi Radeon HD 7570 from eBay and applied the same hacksaw treatment. the card outputs fine, and Windows Update installed the latest supported AMD Catalyst driver and Control Center application automatically. this driver coexists peacefully with the GeForce one, and after extensive testing it did not interfere with 3D application functionality, G-Sync variable refresh rate stuff, display detection or anything else. after around a month of 24/7 use there have been no stability issues, but I will update this page if I run into anything. excluding the testing and experimentation with the first card, this mod takes less than 20 minutes and gives 2 extra display outputs for £5 each, and with minimal PCIe lane sacrifices. the tiny axial fan on the 7570 moves almost no air and makes an annoying noise, so I removed this along with the plasic shroud. as the exposed heatsink sits just ahead of the door panel intake fan in my case, there is still sufficient cooling and the die does not exceed 60C as reported by MSI Afterburner.