This raises the interesting question of what kind of speeds your PCIe device will require. On one hand more bandwidth is nice, on the other hand it also requires more SerDes channels, and not all PCIe slots allow for every card to be installed. While any card of any configuration (x1, x4, x8 or x16) will fit and work in an x16 slot (mechanical), smaller slots may not physically allow a larger card to fit. Some connectors have an ‘open-ended’ configuration, where you can fit for example an x16 card into an x1 slot if so inclined. Other connectors can be ‘modded’ to allow such larger cards to fit unless warranty is a concern.
The flexibility of PCIe means that the bandwidth scales along with the number of bonded lanes as well as the PCIe protocol version. This allows for graceful degradation, where if, say, a PCIe 3.0 card is inserted into a slot that is capable of only PCIe 1.0, the card will still be recognized and work. The available bandwidth will be severely reduced, which may be an issue for the card in question. The same is true with available PCIe lanes, bringing to mind the story of cryptocoin miners who split up x16 PCIe slots into 16 x1 slots, so that they could run an equal number of GPUs or specialized cryptocoin mining cards.
It’s Full of PCIe
This flexibility of PCIe has also led to PCIe lanes being routed out to strange and wonderful new places. Specifications like Intel’s Thunderbolt (now USB 4) include room for multiple lanes of PCIe 3.0, which enables fast external storage solutions as well as external video cards that work as well as internal ones.
Solid-state storage has moved over from the SATA protocol to NVMe, which essentially defines a storage device that is directly attached to the PCIe controller. This change has allowed NVMe storage devices to be installed or even directly integrated on the main logic board.
Clearly PCIe is the thing to look out for these days. We have even seen that System-on-Chips (SoCs), such as those found on Raspberry Pi 4 boards now come with a single PCIe lane that has already been hacked to expand those boards in ways thought inconceivable. As PCIe becomes more pervasive, this seems like a good time to become more acquainted with it.
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