Slot budget is the hidden constraint of server design: a chassis offers a handful of PCIe slots, and GPUs, storage controllers and network adapters compete for them. The documented GRT adapters anchor the realistic widths: x4 for the gigabit bypass card (PCIe 2.1, FF-902TBP) and x16 for the two documented 100G adapters (PCIe 4.0 — the F1102EBPLR bypass card and the FF-1102E). The 25G F2502E-OCP reaches its host through a Gen 3.0 x8 interface, but in OCP mezzanine form, not as a standard PCIe card. Match the adapter to the slot your chassis actually exposes, electrically as well as mechanically.
Generation matters as much as width. A PCIe 4.0 x16 slot delivers roughly double the bandwidth of PCIe 3.0 x16; the two documented 100G adapters — the F1102EBPLR bypass card and the FF-1102E — are specified against PCIe 4.0 x16 (16 GT/s) so their two 100G ports never queue behind the bus. When you inquire, tell us the slot generation and electrical width your server exposes — a mechanical x16 slot wired for x8 is the most common cause of "slow 100G card" reports in the industry.
The range by slot
- PCIe x4 — gigabit bypass and utility adapters
- PCIe Gen 3.0 x8 — the host interface of the 25G OCP mezzanine card (OCP form, not a standard card)
- PCIe x16 — the documented 100G adapters, F1102EBPLR and FF-1102E (Gen 4.0, 16 GT/s)
- Legacy PCI — retained in the wider range for long-life platforms
Will a PCIe 4.0 card work in a PCIe 3.0 slot?
PCIe is backward compatible and the card will run, but a 100G adapter in a Gen 3.0 x16 slot is bandwidth-limited. For full line rate on both ports, use a Gen 4.0 x16 slot.
Do brackets come in both heights?
Key models such as the FF-1102E document both full-height and low-profile brackets. State your chassis bracket requirement in the inquiry.