35T, 75T, 100T or M.2: which DMA board to buy
How the 35T, 75T, 100T and M.2 classes differ in capacity, USB bridge and slot fit, and why the number is not a stealth rating.
Short answer
The number is FPGA logic capacity, not a safety score: 35T suits radar-only use, 75T has the widest firmware support and 100T the most headroom. Choose M.2 if no PCIe slot is free. Buy the class your firmware provider publishes images for, then check that the card physically fits the slot.
On this page8
What do 35T, 75T and 100T mean?
35T, 75T and 100T are Xilinx Artix-7 part numbers (XC7A35T, XC7A75T and XC7A100T), and the number is an approximate logic-cell count in thousands. A bigger FPGA can hold a larger bitstream, so it can carry a more elaborate firmware image and more logic for higher sustained read rates. That is the whole technical difference, and it is not a detection rating. A 100T running a low-effort generic image is more exposed than a 75T running a good one.
How the four board classes compare
These are practical differences rather than marketing claims. Of everything in the table, firmware availability should decide your purchase, because a board nobody builds images for is of no use.
| Class | Form factor | Typical bridges | Best for | Watch out for |
|---|---|---|---|---|
| 35T | Low-profile PCIe x1 | FT601 data, CH347 flash | Radar-only builds and cheap first setups | Least firmware headroom; some providers no longer publish new images for it |
| 75T | PCIe x1 or x4, full height | FT601 data, CH347 flash | The default choice — widest firmware support in the market | Board revisions vary; the silkscreen model matters when ordering firmware |
| 100T | PCIe x1 or x4, full height | FT601 data, CH347 flash | Highest read throughput and the most complex images | Costs more for headroom many builds never use |
| M.2 | M.2 2280, keyed for an NVMe slot | Varies by board — confirm before buying | Small-form-factor and laptop-style game machines with no free PCIe slot | Thermals in a cramped slot; fewer firmware images than 75T |
Two boards listed as "75T" can differ in PCB revision, USB bridge and flash chip, so photograph the silkscreen before you order firmware.
What does your game PC need for any of these boards?
Check these requirements before you spend money, rather than after the box arrives.
- Slot
- One free PCIe slot (x1 electrically is enough) or one free M.2 NVMe slot
- Clearance
- Physical room beside the GPU — measure, do not eyeball
- Bracket
- A free rear slot opening for a full-height card
- Cable
- A real USB 3 data cable, not a charge-only cable
- Second PC port
- A rear-panel USB 3 port. Not a front header, not a hub, not a dock
- BIOS
- Able to enumerate an unknown PCIe device; virtualisation settings adjustable
Warning
Which USB-C port is for data and which for flashing?
Almost every modern board has two USB-C sockets: the flashing port, which drives the CH347 bridge, and the data port, which drives the FT601. The data port is the one you use once firmware is on the card. If the second PC is plugged into the flashing port, the reader never sees the device, which first-timers mistake for a dead card. Follow the board maker's marking whenever one exists, and on an unlabelled board the data port is generally the one further from the PCIe fingers.
Tip
What actually affects read rate?
People choose an FPGA class hoping for more throughput, then lose most of it to the USB path. Cable quality, port generation and whether the link negotiated USB 3 at all matter far more to the result than 75T versus 100T. Measure your read rate before you blame the board; the read speed test takes two minutes and has its own guide.
What to check before you pay for a board
- The firmware you intend to buy is published for this exact board, not just for its FPGA class
- You have photographed or written down the board's silkscreen model and revision
- The card physically fits the slot and clears the GPU
- You know which socket is the data port and which is the flashing port
- You have a known-good USB 3 cable, or you are buying one with the card
- The game you play has a live status row that makes the purchase worthwhile
Common questions about buying a board
Is a 100T worth the extra money over a 75T?
Only if your firmware provider ships an image that uses the extra headroom, or if you want the highest sustained read rates. A radar or ESP build on a 75T-supported title needs neither, so spend the money on a decent second PC and a proper cable.
Can I reuse a card I bought from another seller?
Often yes, if firmware exists for that exact board, but the class label on an old listing is not enough to confirm that. Before you buy an image, send a photo that shows the board, its silkscreen and the FPGA marking.
Does an M.2 card perform worse than a PCIe card?
Not inherently, because an M.2 NVMe slot is PCIe underneath. What differs in practice is the thermal headroom in a tight slot and the smaller library of published firmware images.
Do I need an x4 or x16 slot?
No, these boards are electrically x1, but an x4 or x16 slot works fine and is often easier to fit physically. What matters is clearance, not lane count.
Sources
The rest comes from our own bench work: we learned the port layout, slot fit and cable effects by handling these boards, and which firmware is published for which board reflects what we see in the market.
- 01AMD/Xilinx DS180, 7 Series FPGAs Data Sheet: Overview
the Artix-7 part numbers and per-part logic capacity behind the 35T, 75T and 100T labels
docs.amd.com
- 02pcileech-fpga (Ulf Frisk)
which Artix-7 board targets exist in the open gateware, the origin of these class labels
github.com
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