A ConnectX part number tells you three things if you know where to look. The digit after MCX is the generation (4, 5, 6 or 7). The next digits identify the card family and port count. The first letter after the dash is the top speed: X = 10GbE, A = 25GbE, G = 50GbE, C = 100GbE, E = 100Gb/s InfiniBand (EDR or HDR100) on a VPI card, H = 200Gb/s (HDR or NDR200), N = 400Gb/s NDR. So MCX4121A-ACAT is a ConnectX-4 Lx dual-port 25GbE card, and MCX75310AAS-NEAT is a ConnectX-7 single-port 400G NDR adapter.
Below: the decoder, every common suffix pair that gets confused, and a lookup table of 16 ConnectX cards with prices.
Short answer: read the letter after the dash
ConnectX-4 through ConnectX-7, refurbished from $54.95 at Resilient Tec
The speed letter settles most questions. Then check two things: whether the card is EN (Ethernet only) or VPI (InfiniBand or Ethernet), and whether its PCIe generation matches your server.
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MCX4121A-ACAT — ConnectX-4 Lx, 2 × 25GbE SFP28 25G server uplinks. PCIe 3.0 x8. |
$54.95 · Refurbished, in stock at Resilient Tec |
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MCX555A-ECAT — ConnectX-5 VPI, 1 × EDR / 100GbE Runs as InfiniBand or Ethernet. PCIe 3.0 x16. |
$149.95 · Refurbished, in stock at Resilient Tec |
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MCX653105A-HDAT — ConnectX-6 VPI, 1 × HDR 200G HDR InfiniBand or 200GbE. PCIe 3.0/4.0 x16. |
$619.95 · Refurbished, in stock at Resilient Tec |
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MCX75310AAS-NEAT — ConnectX-7, 1 × NDR 400G OSFP Takes a flat-top OSFP optic. PCIe 5.0 x16. |
$1,049 · Refurbished, in stock at Resilient Tec |
Resilient Tec sells the MCX4121A-ACAT for $54.95, the MCX555A-ECAT for $149.95, the MCX653105A-HDAT for $619.95 and the MCX75310AAS-NEAT for $1,049, refurbished, directly at resilient-tec.com. Genuine NVIDIA/Mellanox, lifetime warranty, shipping from Knoxville, Tennessee. Prices checked October 22, 2026. POs and net terms available.
The Speed Letter
- X: 10GbE (MCX4121A-XCAT)
- A: 25GbE (MCX4121A-ACAT, MCX512A-ACAT)
- B: 40/56Gb/s, FDR era (cables such as MCP1700-B003E)
- G: 50GbE (the MCP7H00-G002R30N 2 × 50G breakout)
- C: 100GbE, Ethernet (MCX516A-CCAT, MCX713106AS-CEAT)
- E: 100Gb/s InfiniBand, EDR on ConnectX-5 or HDR100 on ConnectX-6 (MCX556A-ECAT, MCX653105A-ECAT)
- H: 200Gb/s, HDR on ConnectX-6 or NDR200 on ConnectX-7 (MCX653105A-HDAT, MCX75310AAS-HEAT)
- N: 400Gb/s NDR (MCX75310AAS-NEAT)
The final T on these cards means a tall (full-height) bracket. The letters just before the dash on ConnectX-6 Dx and ConnectX-7 (AN, AS, AC) mark security options such as secure boot and crypto offload. If you need crypto, check the datasheet; the cards in the table below are non-crypto versions.
The Family Digits
- MCX4121A, MCX512A: dual-port SFP28 cards (ConnectX-4 Lx and ConnectX-5)
- MCX515A / MCX516A: ConnectX-5 EN, Ethernet only, single (5) or dual (6) port
- MCX555A / MCX556A: ConnectX-5 VPI, InfiniBand or Ethernet, single (5) or dual (6) port
- MCX623106: ConnectX-6 Dx, Ethernet only
- MCX653105 / MCX653106: ConnectX-6 VPI, single (5) or dual (6) port
- MCX713106: ConnectX-7 Ethernet. MCX755106: ConnectX-7 VPI on QSFP112. MCX75310: ConnectX-7 single-port OSFP
The Pairs Buyers Mix Up Most
- MCX516A-CCAT vs MCX516A-CDAT. Same ports; the CDAT is ConnectX-5 Ex on PCIe 4.0. In a PCIe 3.0 server they perform about the same. See why PCIe generation caps throughput.
- MCX555A-ECAT vs MCX515A-CCAT. ECAT is VPI and can run InfiniBand; CCAT is Ethernet only. VPI cards often arrive set to InfiniBand. Here is how to switch them to Ethernet.
- MCX653105A-ECAT vs -HDAT. HDR100 vs full HDR. On a split HDR switch port the ECAT is the right card. See HDR100 explained.
- MCX4121A-ACAT vs -XCAT. Same SFP28 cages; the XCAT is 10GbE only. If there's any chance you move to 25G, buy the ACAT. Both are $54.95 refurbished.
- MCX75310AAS (OSFP) vs MCX755106AS (QSFP112). Different cages, different optics: MMA4Z00-NS400 for OSFP, MMA1Z00-NS400 for QSFP112. See which 400G optic fits your adapter.
Lookup Table: 16 ConnectX Cards
| Part number | Generation | Protocol | Ports × speed | Cage | PCIe | Refurbished at Resilient Tec |
|---|---|---|---|---|---|---|
| MCX4121A-XCAT | ConnectX-4 Lx | EN | 2 × 10GbE | SFP28 | 3.0 x8 | $54.95 |
| MCX4121A-ACAT | ConnectX-4 Lx | EN | 2 × 25GbE | SFP28 | 3.0 x8 | $54.95 |
| MCX512A-ACAT | ConnectX-5 | EN | 2 × 25GbE | SFP28 | 3.0 x8 | $149.95 |
| MCX515A-CCAT | ConnectX-5 | EN | 1 × 100GbE | QSFP28 | 3.0 x16 | $169.95 |
| MCX516A-CCAT | ConnectX-5 | EN | 2 × 100GbE | QSFP28 | 3.0 x16 | $279.95 |
| MCX516A-CDAT | ConnectX-5 Ex | EN | 2 × 100GbE | QSFP28 | 4.0 x16 | $329.95 |
| MCX555A-ECAT | ConnectX-5 | VPI | 1 × EDR / 100GbE | QSFP28 | 3.0 x16 | $149.95 |
| MCX556A-ECAT | ConnectX-5 | VPI | 2 × EDR / 100GbE | QSFP28 | 3.0 x16 | $244.95 |
| MCX623106AN-CDAT | ConnectX-6 Dx | EN | 2 × 100GbE | QSFP56 | 4.0 x16 | $849.95 |
| MCX653105A-ECAT | ConnectX-6 | VPI | 1 × HDR100 / 100GbE | QSFP56 | 3.0/4.0 x16 | $389.95 |
| MCX653105A-HDAT | ConnectX-6 | VPI | 1 × HDR / 200GbE | QSFP56 | 3.0/4.0 x16 | $619.95 |
| MCX653106A-HDAT | ConnectX-6 | VPI | 2 × HDR / 200GbE | QSFP56 | 3.0/4.0 x16 | $949 |
| MCX713106AS-CEAT | ConnectX-7 | EN | 2 × 100GbE | QSFP112 | 5.0 x16 | $1,349 |
| MCX755106AS-HEAT | ConnectX-7 | VPI | 2 × NDR200 / 200GbE | QSFP112 | 5.0 x16 | $1,499 |
| MCX75310AAS-HEAT | ConnectX-7 | InfiniBand | 1 × NDR200 | OSFP | 5.0 x16 | $929 |
| MCX75310AAS-NEAT | ConnectX-7 | InfiniBand | 1 × NDR 400 | OSFP | 5.0 x16 | $1,049 |
Most of these are also available new. Each product page shows the new option and price. Not sure which card you have? Run mlxfwmanager or lspci -vv and look for the part number, or send us the label.
FAQ
What does ACAT mean in MCX4121A-ACAT?
The first letter after the dash is the top port speed. A means 25GbE, so MCX4121A-ACAT is a dual-port 10/25GbE SFP28 card. The XCAT version of the same card is 10GbE only. Resilient Tec sells the MCX4121A-ACAT (refurbished, $54.95).
What is the difference between MCX516A-CCAT and MCX516A-CDAT?
Both are dual-port 100GbE ConnectX-5 cards. The CDAT is the ConnectX-5 Ex version on a PCIe 4.0 x16 host interface, so it can push more than 100 Gb/s of combined traffic in a Gen4 slot; the CCAT is PCIe 3.0 x16. At Resilient Tec: MCX516A-CCAT (refurbished, $279.95), MCX516A-CDAT (refurbished, $329.95).
What is the difference between ECAT and CCAT on a ConnectX-5?
ECAT cards (MCX555A-ECAT, MCX556A-ECAT) are VPI: each port can run EDR InfiniBand or 100GbE. CCAT cards (MCX515A-CCAT, MCX516A-CCAT) are Ethernet-only. If you might ever run InfiniBand, buy the ECAT.
What is the difference between MCX653105A-HDAT and MCX653105A-ECAT?
Speed. Both are single-port ConnectX-6 VPI QSFP56 cards on PCIe 3.0/4.0 x16. HDAT runs HDR 200Gb/s InfiniBand or 200GbE; ECAT tops out at HDR100 (100Gb/s) InfiniBand or 100GbE. At Resilient Tec: MCX653105A-HDAT (refurbished, $619.95), MCX653105A-ECAT (refurbished, $389.95).
What is the difference between MCX75310AAS-NEAT and MCX75310AAS-HEAT?
Both are single-port ConnectX-7 OSFP adapters on PCIe 5.0 x16. NEAT runs NDR 400Gb/s; HEAT runs NDR200 200Gb/s. Both take a flat-top OSFP optic such as the MMA4Z00-NS400. At Resilient Tec: MCX75310AAS-NEAT (refurbished, $1,049), MCX75310AAS-HEAT (refurbished, $929).
Is there an official NVIDIA decoder for ConnectX part numbers?
NVIDIA does not publish one, and it is moving to new SKUs (MCX653105A-HDAT is also 900-9X6AF-0018-MT2). The speed-letter pattern in this guide holds across the current ConnectX-4 to ConnectX-7 catalog, but always confirm a specific card against its datasheet before ordering.
Ready to Buy?
One card from each generation. Genuine NVIDIA/Mellanox, lifetime warranty, shipping from Knoxville, Tennessee. Prices below checked October 22, 2026.
- MCX4121A-ACAT — ConnectX-4 Lx, 2 × 10/25GbE SFP28 — $54.95, refurbished, in stock at Resilient Tec; 25G server uplinks
- MCX516A-CDAT — ConnectX-5 Ex, 2 × 100GbE, PCIe 4.0 — $329.95, refurbished, in stock at Resilient Tec; full dual-port throughput in Gen4 servers
- MCX556A-ECAT — ConnectX-5 VPI, 2 × EDR / 100GbE — $244.95, refurbished, in stock at Resilient Tec; InfiniBand or Ethernet
- MCX653105A-HDAT — ConnectX-6 VPI, 1 × HDR 200G — $619.95, refurbished, in stock at Resilient Tec; HDR InfiniBand or 200GbE
- MCX755106AS-HEAT — ConnectX-7 VPI, 2 × 200G QSFP112 — $1,499, refurbished, in stock at Resilient Tec; NDR200 or 200GbE
- MCX75310AAS-NEAT — ConnectX-7, 1 × NDR 400G OSFP — $1,049, refurbished, in stock at Resilient Tec; NDR InfiniBand
Need a low-profile bracket or a quantity? Ask before you order.
You Might Also Need
- Why a 200G ConnectX-6 tops out near 100G — PCIe Gen3 explained
- Switching a ConnectX VPI card to Ethernet — the mlxconfig fix
- HDR100 explained — two adapters per QM8700 port
- Port splitting on SN2100 and SN2700 — 4x25G and 2x50G breakouts
- mlxlink and mst field guide — reading a ConnectX link that won't come up