Is the built-in Windows 10 USB NCM driver capped at USB 2.0 speeds instead of USB 3.x?

Question

I'm trying to deploy 500GB CAD workstations for the engineering department and the network imaging process is crawling. We are using USB-C ethernet adapters that rely on the built-in Windows 10 NCM driver, but the throughput is completely abysmal. Does anybody know if this driver actually handles true USB3.x bandwith, or is it hardcoded to max out at USB2.0 speeds? Thank you.

Answer 1

Hi Chang,

No, the Windows 10 inbox CDC-NCM driver is not inherently hard-limited to USB 2.0 speeds. If the adapter is actually enumerating as SuperSpeed (USB 3.x) and the NIC is a 1GbE or 2.5GbE-class device, the NCM path can absolutely run above USB 2.0-era throughput. CDC-NCM is just the USB network class/protocol; it does not by itself force High-Speed (480 Mbps) operation. That said, in real-world Windows imaging, the inbox NCM path is often noticeably worse than vendor-specific drivers (Realtek/ASIX) for sustained throughput and CPU efficiency, especially during heavy SMB/WDS/MDT-style deployment.

Hope it's helpful.

Harry.

Answer 2

The provided information does not state any limitation or cap in the Windows USB networking stack or NCM-related class drivers that would restrict them to USB 2.0 speeds when used over a USB 3.x connection. USB bandwidth and speed are determined by:

1. The USB host controller type and its driver stack (xHCI for USB 3.x, EHCI/UHCI/OHCI for USB 2.0 and below).
2. The negotiated device speed (low/full/high/super) and the physical routing of the port.

Windows loads the USB driver stack based on the host controller type, not on the device speed. When a USB 3.x port is correctly routed to an xHCI controller, Windows uses the USB 3.0 (xHCI) stack; when a USB 2.0 port is routed to EHCI, it uses the USB 2.0 stack. Different device speeds can influence which controller is used, but the controller always uses the same driver stack for its generation.

Nothing in the context indicates that the Microsoft-provided USB networking class drivers (including those for USB NCM-type devices) are hardcoded to USB 2.0 bandwidth limits when attached to a USB 3.x controller.

If throughput is abysmal, likely causes outside this information set include:

• The adapter or port negotiating only at USB 2.0 speeds (e.g., cabling, hub, or port routing issues).
• Bandwidth contention or allocation issues on the USB bus (for example, other isochronous or interrupt endpoints monopolizing bandwidth).
• Device- or driver-specific constraints not documented here.

From the available material, there is no documented cap in the built-in Windows 10 USB NCM-related stack that would force a USB 3.x-capable adapter to operate only at USB 2.0 speeds.

---

References:

• USB in Windows - FAQ
• Support for USB 3.0
• USB device class drivers included in Windows
• USB bandwidth allocation