Bringing USB 3 and USB4/Thunderbolt to Windows 98 to 7

xHCI98 is a complete reimplementation of the Windows host controller driver stack that brings true USB 3.x speeds and USB4/Thunderbolt support to Windows 98 SE through Windows 7. The earlier approach used a usbport.sys miniport and intentionally limited controllers to USB 2.0 because usbport.sys has no SuperSpeed concept, which forced awkward workarounds like virtual hubs and speed misreporting. Version 2 replaces usbport.sys, usbhub.sys and related helpers with a single bus driver (xhci98.sys), an xhciuas.sys UAS class driver and a small x86 helper so one binary supports Win98 SE-7 (with a separate x64 build for 64-bit OSes). The new stack powers SuperSpeed ports, supports UAS for modern storage, and preserves compatibility with existing class drivers so third-party drivers still work; Device Manager still labels devices "High Speed" because older OS interfaces predate SuperSpeed.

Real-world hardware revealed many edge cases that shaped the implementation. Shared Intel ports that boot on EHCI are flipped to xHCI by writing USB3_PSSEN and XUSB2PR PCI registers; BIOS IRQ routing bugs (e.g., Dell E7250) required polled event delivery and use of MSI on Vista/7; Sunrise Point controllers publish nonstandard speed tables that needed fallback handling; and many controllers require Linux-style tolerance and vendor-specific quirks (Fresco, ASMedia, AMD, TI, Etron, VIA, etc.). For USB4/Thunderbolt the approach included building an emulator, capturing the laptop’s controller behavior, and writing Stor98 to support hot-pluggable NVMe devices. AI was used for diagrams and build assistance.