Electronic – PCIe PRSNT# signal connection

You need the AC coupling caps to remove excess DC offsets from the transmitter, whether you are on one board or multiple boards, end of subject. You can even try it and have it work, but you , in this case, were just lucky. The caps cost $0.10 per direction for a single lane PCIe.

So, the way PCIe links work is they come up as gen 1 x1 links, then negotiate up to more lanes and higher speeds. If you wire the card with multiple devices connected to the edge connector, only the one connected to lane 0 will work, the rest will not enumerate. Unless, of course, you can reconfigure whatever switch port drives the slot in question to bifurcate the slot into the lane configuration you need. This is certainly not something that you can rely on - it not only requires the switch or bridge to support that configuration, but it also requires that the ability to change the configuration is exposed somewhere. All this will be highly dependent on the exact motherboard in use, the PCIe related chips installed, how they are wired, and how the BIOS is written. Not to mention this also prevents the card from working properly in systems that only connect 1 or 2 lanes instead of all 4, which happens occasionally, though most commonly with x16 slots wired as x8 or x4.