The later specs (Gen 4/5) have incredibly granular power states (L0s, L1, L1 PM Substates). If you buy a cheap riser card or a poorly manufactured SSD, it may ignore the "Electrical Idle" condition in the spec. Result? Your NVMe drive runs hot and draws 10W even when it isn't doing anything.
If you jam a GPU into a slot upside down? No (don't do that). But if a motherboard designer routes traces in a weird order, the spec allows the two devices to say, "Hey, I know Lane 0 is supposed to go to Lane 0, but you sent it to Lane 3. I'll fix it in firmware." pcie spec
Do you have a horror story about a PCIe link that refused to train? Let us know in the comments below. The later specs (Gen 4/5) have incredibly granular
Compliance to the spec saves watts. The draft spec for PCIe 7.0 is already floating around. It promises 128 GT/s (512 GB/s on x16). But here is the catch: to hit that speed, the spec will likely require optical cables for any trace longer than a few inches. Your NVMe drive runs hot and draws 10W
Why the 300-page document is the real hero of your high-performance computing.
Next time you plug in a Gen 5 SSD and it drops down to Gen 4 speeds, don't blame the hardware. Somewhere, the spec did its job. The link trained, the equalization failed, and the devices agreed on a slower, safer speed to keep your data intact.