Both are dual-port 100GbE ConnectX-5 adapters with QSFP28 connectors. The difference is the bus: the MCX516A-CCAT is PCIe 3.0 x16, while the MCX516A-CDAT (ConnectX-5 Ex) is PCIe 4.0 x16. In a PCIe 3.0 server they perform almost identically; only a PCIe 4.0 host lets the CDAT sustain both 100G ports at line rate.
What the two part numbers actually are
The two cards share the same MCX516A prefix and the same dual-port 100GbE QSFP28 physical design, which is why buyers mix them up. The suffix is what separates them:
- MCX516A-CCAT — ConnectX-5, PCIe 3.0 x16 host interface, 2x QSFP28 100GbE ports.
- MCX516A-CDAT — ConnectX-5 Ex, PCIe 4.0 x16 host interface, 2x QSFP28 100GbE ports.
One practical warning: Mellanox suffix letters do not map to the same PCIe generation across the ConnectX-4, ConnectX-5 and ConnectX-6 families, so a letter-based rule of thumb learned on one card can mislead you on another. Always check the full part number against the NVIDIA spec sheet — or read our piece on PCIe generations before you assume a card will run at full speed. If the sticker is unclear, send us the part number and we will identify it.
The bandwidth math for dual-port 100GbE
This is where the two cards actually diverge. A PCIe 3.0 x16 link carries roughly 126 Gb/s per direction. Dual-port 100GbE at line rate needs about 200 Gb/s per direction, because each port moves 100 Gb/s in and 100 Gb/s out. A PCIe 4.0 x16 link roughly doubles that ceiling to about 252 Gb/s per direction.
| Spec | MCX516A-CCAT | MCX516A-CDAT |
|---|---|---|
| ASIC family | ConnectX-5 | ConnectX-5 Ex |
| Host interface | PCIe 3.0 x16 | PCIe 4.0 x16 |
| Bus ceiling (per direction) | ~126 Gb/s | ~252 Gb/s |
| Single 100GbE port at line rate | Yes | Yes |
| Both 100GbE ports at line rate | No — combined ceiling around 120 Gb/s per direction | Yes |
In plain terms: a CCAT runs one 100G port at close to line rate, but if you push both ports hard at the same time, the PCIe 3.0 bus becomes the bottleneck and combined throughput plateaus near 120 Gb/s per direction. The CDAT has headroom to feed both ports at full rate — but only if the host slots are PCIe 4.0. Drop the CDAT into a Gen3 machine and it links down to Gen3 speed, where it behaves like the CCAT.
What is identical — and what that means for your build
Because the port side is identical, the choice does not change your cabling or software plan:
- Both expose 2x QSFP28 100GbE ports and use the same QSFP28 DACs, AOCs and transceivers.
- Both run the same Mellanox/NVIDIA driver stack (MLNX_OFED on Linux, the standard driver package on Windows), so the configuration workflow is identical.
- Both are backward compatible: the PCIe 4.0 CDAT works in a PCIe 3.0 slot at Gen3 speed, just like a CCAT.
- Both pair naturally with Spectrum-series switches such as the Mellanox SN2700 32-port 100GbE switch — see our SN2700 vs SN3700 switch selection guide for picking the switch side.
Which one fits your host
Match the card to the generation of the slots you will actually use:
- PCIe 3.0 hosts — platforms built on first- and second-generation Intel Xeon Scalable CPUs, such as the HPE ProLiant DL380 Gen10 or Dell PowerEdge R730/R740. Here the CCAT already saturates everything the bus can carry, and a CDAT buys you nothing today.
- PCIe 4.0 hosts — platforms on Intel Ice Lake or Sapphire Rapids Xeon, or AMD EPYC Rome and newer, such as the Dell PowerEdge R650/R750 generation. This is the only environment where the CDAT pulls ahead, and only for workloads that saturate both ports.
- Card will move between servers — if you plan to reuse the adapter in a newer host later, the CDAT keeps that upgrade path open; a CCAT will always be capped at Gen3.
- Need 200G per port instead of 100G — neither card is the right tool; look at ConnectX-6 HDR-class adapters such as the MCX653106A-ECAT dual-port HDR100 card instead.
What to check before you buy a used ConnectX-5
Used ConnectX-5 cards are common on the secondary market, and most of them work exactly as advertised — but a few checks separate a good unit from a frustrating one:
- Read the full part number. CCAT and CDAT stickers look nearly identical at a glance. Confirm the exact suffix before you buy, not after.
- Ask about the PSID. OEM-branded cards can carry vendor-specific PSIDs that complicate firmware updates. Ask which PSID the card reports and whether the firmware matches a standard NVIDIA image.
- Check the hardware condition. Confirm the heatsink is present and the QSFP28 cages are undamaged, especially if the card was pulled from a dense rack.
- Buy from tested units. Cards we list are used MCX516A-CCAT adapters and MCX516A-CDAT (ConnectX-5 Ex) adapters that have been bench-tested on our own line, so the part number, ports and firmware are confirmed before dispatch. Models listed on zhongxindata.hk are in stock.
Frequently asked questions
Is the MCX516A-CDAT backward compatible with PCIe 3.0 slots?
Yes. It links down to PCIe 3.0 x16 and then performs the same as a CCAT. You lose the Gen4 headroom, nothing else.
Can the CCAT use both 100GbE ports at the same time?
Yes, both ports work simultaneously, but combined throughput per direction tops out around 120 Gb/s on the PCIe 3.0 x16 bus. For most workloads that is not a problem; for dual-port line-rate testing it is.
Do the two cards use the same cables and transceivers?
Yes. Both use QSFP28, so the same DACs, AOCs and 100G transceivers work on either card.
Which card should I put in a DL380 Gen10?
The DL380 Gen10 is a PCIe 3.0 platform, so the CCAT is the sensible match. The CDAT works but runs at Gen3 speed with no benefit.
How do I tell which card I have if the label is worn?
Check the part number printed on the PCB or read it from the firmware (mlxconfig or lspci output). If you are not sure, send us the number and we will identify it.
Send the part number and quantity and we will check availability. WhatsApp +86 13068616914 · zhongxindata.hk