xhci98

xHCI98 is a USB host controller driver (HCD) for xHCI (USB 3.x) controllers on Windows 98 SE, ME, 2000, XP (x86/x64), Vista (x86/x64) and 7 (x86/x64).

Experimental support for USB4 and Thunderbolt 3/4 is also included, on those systems and on Windows 8, 8.1 and 10 (x86/x64).

Supported:

• SuperSpeed devices and hubs:
  • USB 3.2 Gen 1, 5 Gbit/s
  • SuperSpeedPlus: USB 3.2 Gen 2 and Gen 1x2 (10 Gbit/s), and Gen 2x2 (20 Gbit/s)
• USB 2.0 and 1.1 (High, Full and Low Speed) devices and hubs
• UAS (USB Attached SCSI) storage, through a second driver, xhciuas.sys
• Thunderbolt 3 and USB4 docks and NVMe enclosures through a third driver, xhcicm.sys

It is built to Intel's xHCI specification and tested mainly on Intel machines. Other vendors' controllers carry no guarantee, though best effort has been made for the quirks of Fresco Logic, ASMedia, AMD, TI, Etron, VIA and some Intel controllers, even ones built to the xHCI 0.96 draft standard.

This is a solo human's project with AI assistance, so bugs are not unexpected. Please report them.

Contents: Motivation - SuperSpeed and UAS - Thunderbolt 3 and USB4 - The xHCI98 USB Tree - Benchmarking a disk - Installation Steps (Downloads, SETUP.EXE, by hand) - Tuning - What is tested - The package - Reporting a bug - Known limitations - Building - Repository Layout - Documentation - AI usage - References - Licensing

My 2020 ThinkPad P14s Gen 1 on Windows 98 SE with a USB 3.0 hub, two UAS drives, USB Ethernet, USB Audio and a mouse. All run on the xHCI controller, the drives at SuperSpeed.

Windows 7 with an ORICO USB4 NVMe enclosure on the Thunderbolt 3 port, through xhcicm.sys and Stor98: CrystalDiskMark sequential 1151 MB/s read, 1013 MB/s write.

The same enclosure on Windows 98 SE: about 210 MB/s read and 256 MB/s write, limited by Windows 98's own storage stack. With S98VSD.VXD, 2 MiB reads reach about 1120 MB/s and writes about 880 MB/s.

The xHCI98 USB Tree and Device Manager on Windows 98 SE, with an ASMedia USB4 NVMe enclosure on a USB4 host. Emulated hardware in QEMU.

• Video by Omores featuring this driver in its earlier USB 2.0 days:

  

• My demo video: https://www.youtube.com/watch?v=AU77f9CSbYc

• Blog post xHCI98v1: https://yeokhengmeng.com/2026/08/xhci98-usb-host-driver/

• Blog post xHCI98v2 v3: https://yeokhengmeng.com/2026/10/xhci98-usb3-usb4/

Motivation

PCs from the mid-2010s onwards have xHCI-only USB chipsets. Windows 98 shipped with USB 1.1 (UHCI/OHCI) drivers and gained USB 2.0 (EHCI) through NUSB's back-ported stack; Windows 2000 gained EHCI in SP4. Windows 7 has no USB 3 stack of its own either.

Without xHCI support, even keyboards, mice and flash drives need the BIOS's legacy support, cannot be hotplugged, and devices such as Ethernet and audio do not work at all. This project fills that gap.

SuperSpeed and UAS

The P14s Gen 1 under Windows 98 SE with NUSB: the MSSU10-128GSR flash drive at SuperSpeed through xhciuas.sys. ATTO Disk Benchmark (Direct I/O) gives about 201 to 215 MB/s write and 196 to 221 MB/s read from 512 KB transfers upward.

• A UAS-capable drive gets UAS; anything else gets Windows' own usbstor.sys (Bulk-Only), at whatever speed it connects. A drive that offers both can be forced to Bulk-Only (XhciForceBulkOnly, see Tuning).
• Device Manager and other Windows tools on these systems may show a SuperSpeed device as High Speed at most: the interface they read predates SuperSpeed.

Thunderbolt 3 and USB4

xhcicm.sys brings Thunderbolt 3 and USB4 docks, enclosures and NVMe cases to these systems. Devices inside them (an NVMe drive, a dock's USB controller or network adapter) appear in Device Manager within seconds of the plug, with no Refresh, and leave on unplug. A device the BIOS connected at power-on is kept as it is.

• Intel Thunderbolt 2 and 3 controllers, and USB4-generation Intel ones while their firmware runs its own connection manager: the driver approves each device the firmware announces.
• USB4 hosts whose firmware has no connection manager (AMD, ASMedia ASM4242 on AM5 X870 boards, Intel Lunar Lake and later, Barlow Ridge): the driver is the connection manager and builds the tunnels.

Device Manager names each controller by its generation, then its maker and product: Thunderbolt 2 and Thunderbolt 3 (TB2, TB3) controllers, and USB4 Routers (the USB4 host router).

Controller	PCI ids (8086: unless named)	In Device Manager
Falcon Ridge (Thunderbolt 2)	156A, 156C	xHCI98 TB2 Controller (Intel Falcon Ridge)
Alpine Ridge (Thunderbolt 3)	15BF, 1575, 1577, 15D2, 15D9	xHCI98 TB3 Controller (Intel Alpine Ridge)
Titan Ridge (Thunderbolt 3)	15E8, 15EB	xHCI98 TB3 Controller (Intel Titan Ridge)
Ice Lake	8A0D, 8A17	xHCI98 TB3 Controller (Intel Ice Lake)
Maple Ridge	1134, 1137	xHCI98 USB4 Router (Intel Maple Ridge)
Tiger Lake, Alder Lake, Raptor Lake, Meteor Lake	9A1B, 9A1D, 9A1F, 9A21; 463E, 466D; A73E, A76D; 7EB2, 7EC2, 7EC3	xHCI98 USB4 Router (Intel Tiger Lake), (Intel Alder Lake), (Intel Raptor Lake), (Intel Meteor Lake)
Lunar Lake, Panther Lake, Wildcat Lake	A833, A834; E333, E334, E433, E434; 4D33	xHCI98 USB4 Router (Intel Lunar Lake), (Intel Panther Lake), (Intel Wildcat Lake)
Barlow Ridge	5781, 5784	xHCI98 USB4 Router (Intel Barlow Ridge)
AMD Pink Sardine	1022:1668, 1022:1669	xHCI98 USB4 Router (AMD Pink Sardine)
ASMedia and any other USB4 host	PCI class 0C0340	xHCI98 USB4 Router

Before you start: 64-bit Windows

On Vista x64 to 10 x64, test-signing mode must stay on for as long as the Thunderbolt 3 / USB4 support is installed, even with nothing plugged in. Windows loads that driver at boot; without test-signing, 8, 8.1 and 10 stop in Automatic Repair and 7 x64 silently rolls the install back. A feature update, turning Secure Boot on or a boot repair can turn test-signing off. See test-signing mode.

Before you start: the BIOS

• Boot in legacy (CSM) mode, as for every system here.
• Thunderbolt BIOS Assist off. With it on, the BIOS switches the controller off when nothing is attached at power-on, and the driver cannot switch it back on (on the P14s Gen 1 the controller disappears altogether).
• Security level User Authorization or No Security. Secure Connect, DisplayPort-only and USB-only are not supported.
• Pre-boot support (boot from Thunderbolt) may be on or off. When on, a device attached at power-on keeps working under the driver.

Approving and removing

• Names: on Windows 2000 to 7 the controller's PCI ports show as "xHCI98 Thunderbolt PCI Bridge" or "xHCI98 USB4 PCI Bridge" (Windows' own bridge driver with this package's filter).
• Approval: by default (XhciCmApprove 1) every device plugged in is approved at once. A device with a PCI Express tunnel can read and write all of the machine's memory, and these systems cannot stop it. Where untrusted people can reach the port, set XhciCmApprove to 0: only devices the BIOS connected at power-on then work.

Removing a device safely. Close its open files first, then:

Windows	How
2000	Stop it in "Unplug or Eject Hardware", then unplug. Without the stop, Windows 2000 shows "Unsafe Removal of Device".
XP, Vista, 7	Stop it in "Safely Remove Hardware", then unplug.
98 SE, ME	No such dialog lists them (ME's "Unplug or Eject Hardware", and NUSB 3.3's on 98 SE, list USB storage only): use the xHCI98 USB Tree or INSTALL /eject. Until you unplug, Device Manager's Refresh can start the device again.

• A dock is listed under a generic PCI bridge name; stopping it stops everything in the dock.
• A device missing from Windows' list (its first plug, or after a disable and enable or a driver update): stop it in the USB Tree run as an administrator. Otherwise close every program using it, unplug it and plug it in again; Windows lists it from then on.
• For scripts: INSTALL /devices and INSTALL /eject (tools\xhciinst\readme.txt).

NVMe drives

An NVMe drive in an enclosure needs an NVMe driver. Stor98, shipped with this package, is that driver where Windows has none, or where Windows' own one handles an unplug badly. xhcicm.sys runs the tunnel; Stor98 runs the drive.

Windows	Driver of a tunnelled NVMe drive	Why
98 SE, ME, 2000, XP, Vista, 8	Stor98	no NVMe driver of its own
7	Stor98	its stornvme comes only with update KB2990941, untested behind a tunnel
8.1	Stor98 (internal drives keep stornvme)	its stornvme hangs a write for good on an unplug without Safely Remove
10	Windows' own stornvme; Stor98 is opt-in	stornvme handles an unplug cleanly

Use Safely Remove before unplugging a drive, on every system.

Stor98 is only for NVMe drives behind a Thunderbolt or USB4 port, not internal ones. SETUP.EXE puts it only on tunnel drives. On 2000 to 7 Windows may offer it for an internal NVMe drive with no driver: decline. On Vista x64, 7 x64 and 8, once the test certificate is trusted, Windows may put it on such a drive without asking; the uninstall then leaves it on that drive.

• SETUP.EXE installs Stor98 with the Thunderbolt 3 / USB4 support (its box, ticked with it) and updates an earlier Stor98. By hand: Update Driver on the drive's NVMe controller -> Have Disk -> release-x86\ or release-x64\.
• On 98 SE and ME, S98VSD.VXD lets reads and writes of up to 2 MiB reach Stor98 whole, for much faster transfers. SETUP.EXE installs it with Stor98.
• Stor98's settings and limits: stor98-readme.txt beside it, and the release notes.

Things to know

• Before standby or hibernation, stop and unplug every Thunderbolt or USB4 device. Standby with one attached, or with an Ice Lake or later controller, is not supported.
• 98 SE and ME: a device plugged in after the start needs an interrupt from the BIOS (the P14s Gen 1 gives one). If it stays at Code 29, attach it at power-on with pre-boot support on.
• 98 SE and ME: the Thunderbolt driver stays loaded until a restart, so a disable, update or removal takes effect after one.
• If the platform switches a USB4 controller off behind Windows' back, disable and enable the controller, or restart.
• Settings: Tuning. Detail: the release notes' Thunderbolt and USB4 sections and known limitations.

The xHCI98 USB Tree

XHCITR.EXE (XHCITR64.EXE on 64-bit Windows) shows every USB and Thunderbolt/USB4 controller and device. It needs no administrator rights. The install starts it at login as a notification-area icon (untick Start at login in its menus to stop that); it is also in tools\xhcitr\.

• Safely Remove: left-click the icon, pick the device and unplug when told. Works for USB storage on 98 SE and ME too.
• Notices: a "can run faster" balloon for a device on a slower port or behind a slower hub, a red icon while something needs you, and a warning after a Thunderbolt or USB4 device is removed unexpectedly.
• Details: each item's speed, port, IDs, driver, Device Manager status, resources and PCI configuration. File > Save Report writes it all to a text file for a bug report.
• Driver log: each controller has a "Driver log" item, included in Save Report. View > Logging level... sets either driver's level (default 2, 0 for off; takes effect after a restart).
• Snapshot: Save Report ends with the driver's snapshot (its device report and decoded state). File > Save Snapshot..., XHCITR /snapshot, /dump and /probe write the snapshot's files themselves, for when a maintainer asks for them.

Details: the release notes' USB Tree section.

Benchmarking a disk

To benchmark a disk, use CrystalDiskMark or ATTO Disk Benchmark (suggestions, not part of this package). XHCIPERF stays a developer diagnostic in the source tree (xhciperf\), not shipped.

Installation Steps

Downloads

Each release has three zips. Each holds everything in the one before it, so pick one:

Download	What it holds
xhci98-<version>.zip	The xHCI98 drivers (USB 3, UAS, Thunderbolt 3 / USB4), Stor98, the installer and the tools. Also NUSB 3.3's seven Windows 98 SE storage files in USBDRV\NUSB33\, which the installer offers on 98 SE when NUSB is not installed (an installed NUSB is kept).
xhci98-<version>-free.zip	Adds the free USB class drivers (audio, webcam, Ethernet and more) from usb-wdm-free in USBDRV\FREE\. Experimental: they may not work with every device and can make Windows unstable. It includes the CamCheck webcam preview tool in USBDRV\FREE\tools\camcheck\.
xhci98-<version>-nonfree.zip	Adds a pack of other manufacturers' USB drivers from usb-wdm-nonfree in USBDRV\NONFREE\, not this project's work.

Nothing from USBDRV\ is installed unless you tick it on the installer's Other USB drivers page. On Windows 98 SE and ME the free and non-free drivers are copied only: when the hardware wizard asks for a driver, point it at the package's folder, USBDRV\FREE\<class>\<package>\<folder> (or USBDRV\NONFREE\...) in the install directory.

Requirements

Windows	What to install first
98 SE	NUSB 3.3 or 3.6 for USB storage, UAS included. Without it HID and audio work but storage has no driver. SweetLow's stack also works (right-click its root USB2.INF, Install) but has no storage half: a stick shows Code 28 and a UAS drive Code 2 until NUSB's storage files are present. Reboot if asked.
ME	Nothing; a stock ME works, as does SweetLow's stack if already there. Plug an ordinary USB stick in once, so ME copies its storage drivers, before a UAS drive is recognised.
2000 SP4, XP SP3	Nothing.
XP x64 SP2, Vista SP2, 7 SP1 (x86/x64)	Nothing. Vista x64 and 7 x64 need test-signing mode (or F8 at every boot).
8, 8.1, 10 (x86/x64)	Secure Boot off in the firmware setup; the x64 editions also need test-signing mode. Windows' own USB 3 driver stays unless you tick the USB drivers.

• The eject icon on 98 SE comes only with NUSB 3.3's own setup, not with the seven storage files in this download. It lists USB sticks and UAS disks, never a Thunderbolt or USB4 drive: use the xHCI98 USB Tree or INSTALL /eject for those.
• 98 SE storage of any kind needs NUSB's mass-storage files (details).
• On an xHCI-only 98 SE or ME machine, have the Windows CD (or its files) at hand: Windows may ask for files.

Check the machine first (optional, recommended)

Boot real DOS (not a DOS box inside Windows) and run XHCIQUAL from TOOLS\XHCIQUAL\. It says whether the driver can work on the machine before you install anything. A controller with no legacy interrupt pin is not refused: the driver polls it, or uses a message-signalled interrupt on Vista and 7, and XHCIQUAL reports QUALIFIED WITH CAVEATS.

The read-only quick scan answers in one line. The xhci run exercises the controller (handoff, reset, DMA, interrupt, port resets) and ends with a verdict:

XHCIQUAL demo video: https://www.youtube.com/watch?v=Tv6blmBS6Do

Install with SETUP.EXE

You can also install by hand from Device Manager (Install by hand).

1. Unzip the whole package.
2. Double-click SETUP.EXE in its top directory (on 2000 and XP as an administrator; on Vista and later answer Yes when Windows asks).
3. Go through the pages: Welcome, Components, Other USB drivers and Summary. The driver's options are under Settings; the tools go to C:\XHCI98. Nothing changes until you click Install.
4. Answer Windows' unsigned-driver questions. If the Finish page lists steps left for you (a Found New Hardware window, for instance), do them and run SETUP.EXE again. Restart if it offers.

The installer's Components page on Windows 98 SE.

What it does:

• Windows 2000 to 7: installs or updates the driver of every device present and stages the package for devices plugged in later.
• Windows 98 SE and ME: copies the package to the install directory, adds it to the hardware wizard's search path and installs each device through Windows' own installer.
• Thunderbolt 3 / USB4 support (experimental): on 2000 to 7, unticked unless you tick it; the line under it says whether a controller was found. Some laptops show the controller only with a device plugged in, so tick it if yours has the port. It ticks Stor98 too (except on Windows 10). On 2000 to 7 it also puts the filter on the controller's PCI ports so Windows sees devices plugged in later (on 2000, after one restart). Untick the USB drivers to install it alone, for a machine whose USB 3 runs another driver. If the Summary page says "Thunderbolt 3 and USB4 will be turned off (XhciCmMode 0)", go back and check its settings.
• Windows 8, 8.1 and 10: only the Thunderbolt 3 / USB4 support by default; Windows' own USB 3 driver keeps the USB controllers unless you tick the USB drivers. Secure Boot must be off, and on x64 it installs only in test-signing mode (Before you start).

To uninstall, use Remove in Add/Remove Programs (Programs and Features on Vista and later). Every run writes XHCIINST.LOG at the root of the system drive; attach it to a bug report about an install. For scripted installs, see tools\xhciinst\readme.txt.

Details: the release notes' installer section.

Install by hand

1. Put the unzipped package where the machine can read it (floppy, CD, shared folder), and install the prerequisites. On a fresh 98 SE the order is NUSB, then xhci98, then the UAS disk.
2. In Device Manager, find the unrecognised xHCI controller (yellow mark, usually under "Other devices").
3. Properties -> Driver -> Update Driver -> Have Disk -> release-x86\ or release-x64\. It installs as "xHCI98 USB 3 Controller" with "xHCI98 USB 3.x Root Hub" beneath (only SETUP.EXE adds the chipset to the name). 98 SE may ask for its CD. Restart if asked.
4. A Thunderbolt 3 or USB4 controller ("PCI System Peripheral" or "Base System Device") installs the same way. On 2000 to 7, then give each of its PCI ports the filter: Update Driver -> Have Disk -> release-x86\nt\ (32-bit) or release-x64\ (64-bit).
5. A UAS disk or an external hub asks for its driver when plugged in: give it the same directory. On XP every new hub brings the Found New Hardware wizard and the unsigned-driver warning (Continue Anyway).

The controller in Device Manager on the P14s Gen 1 under Windows 98 SE.

64-bit Vista to 10: test-signing mode

The 64-bit drivers are test-signed, so Vista x64 to 10 x64 run them in test-signing mode (or with F8, "Disable Driver Signature Enforcement", at every boot). On 8, 8.1 and 10, turn Secure Boot off in the firmware setup first. Then, once:

1. Open an elevated Command Prompt (Start, type cmd, right-click, Run as administrator).
2. Run bcdedit /set testsigning on. It stays on for every boot until turned off.
3. Restart. "Test Mode" shows on the desktop (bottom right on 7 and later, in the corners on Vista).
4. Install the driver. Windows still says it cannot verify the publisher: choose "Install this driver software anyway". The Driver tab then says "Not digitally signed". Both are expected.

• Check: bcdedit /enum {current} shows testsigning Yes.
• Turn off: bcdedit /set testsigning off and restart. The driver then needs F8 again, or the controller shows Code 39 (Vista) or Code 52 (7).
• With BitLocker on the system drive, suspend it before changing the boot setting, or the next boot asks for the recovery key.
• This is not Microsoft signing: the certificate is the project's own, which no Windows trusts by itself. F8 still works for one boot without test mode.

Installing Windows 2000 or XP, or using the Recovery Console

For a machine whose keyboard or install medium is on the xHCI controller:

1. Copy the files of release-x86\ (release-x64\ for XP x64) to the root of a floppy.
2. Windows 2000 only: from the I386 folder of your Windows 2000 CD, copy USBD.SY_, HIDCLASS.SY_ and HIDPARSE.SY_ to the floppy's root, unchanged (do not expand or rename). The package does not carry them.
3. Press F6 when text-mode Setup offers it, then S, and pick "xHCI98 USB 3.x Host Controller (32-bit Windows 2000/XP)" (the x64 entry on XP x64), or on Windows 2000 the second entry, "xHCI98 USB 3.x Host Controller (32-bit Windows 2000, files from CD)".

• Windows 2000: with a USB keyboard, mouse or stick used during Setup, the first entry leads to STOP c000026c at the first start; the second entry without the three files stops Setup asking for them in drive A: (F3 quits). Plug the USB keyboard and stick in before Setup starts.
• XP and XP x64: have a PS/2 or built-in laptop keyboard at hand. Later in Setup the USB keyboard does not work until a step that first asks about this unsigned driver.
• Pressing F6 needs the BIOS's own USB keyboard support.
• A USB floppy drive works for F6 only if it is one Setup knows: Mitsumi 03EE:6901, Y-E Data 057B:0000 or TEAC 0644:0000 (VID:PID). No INF can add another; otherwise use a floppy drive on the floppy controller.
• A UAS-only disk is not usable until GUI-mode Setup; a flash stick, or a UAS disk that also offers Bulk-Only (most do), is.
• A USB drive present at the partition screen takes C:. Unplug the USB drives you do not need.
• Recovery Console (2000 and XP): the same floppy and F6, then R at the Welcome screen (on 2000, then C). The USB keyboard works throughout.

Details and limits: the release notes' F6 section.

Upgrading the driver

Run SETUP.EXE (see above). By hand: Update Driver on the controller ("xHCI98 USB 3 Controller", or "xHCI98 USB 3.x eXtensible Host Controller" while an older version is installed), then on "xHCI98 USB 3.x Root Hub", pointed at release-x86\ or release-x64\.

• 98 SE and ME: restart afterwards, although Windows does not ask. The old driver runs until then.
• 2000: use Have Disk (Update Driver -> "Display a list of the known drivers" -> Have Disk -> release-x86\) and pick the first model listed. Letting Windows search keeps the old driver.
• XP, Vista and 7: the new driver runs at once, after the unsigned-driver warning; 32-bit Vista and 7 ask for a restart. Vista and 7 do not take a build with the same DriverVer as the installed one.
• A device Windows finds again as new hardware loses its hidusbf setting. Set it again.
• From 2.3.x or earlier: update the controller only; the hubs and composite devices then install by themselves. On 98 SE, XP and XP x64 keep a PS/2 or built-in keyboard and mouse at hand. See From 2.3.x or earlier.
• xhciuas.sys at the same DriverVer: use Have Disk on "xHCI98 USB Attached SCSI Storage"; letting Windows search keeps the cached INF.

Tuning

Each value is a DWORD in a driver (software) key, and also in the machine-wide key HKLM\System\CurrentControlSet\Services\USB, which wins for every controller when the value is there (tuning); restart Windows after a change (for XhciCm*, disabling and enabling the controller also works). The install writes most values (its Settings dialog, and "Advanced...") and an update keeps any you changed.

Driver	Windows	Key (NNNN is the subkey whose DriverDesc names the controller)
xhci98.sys	98 SE, ME	HKLM\System\CurrentControlSet\Services\Class\USB\NNNN
xhci98.sys	2000 to 7	HKLM\SYSTEM\CurrentControlSet\Control\Class\{36FC9E60-C465-11CF-8056-444553540000}\NNNN
xhcicm.sys	98 SE, ME	HKLM\System\CurrentControlSet\Services\Class\System\NNNN
xhcicm.sys	2000 to 7	HKLM\SYSTEM\CurrentControlSet\Control\Class\{4D36E97D-E325-11CE-BFC1-08002BE10318}\NNNN

Value	What it does	Default
XhciLogVerbosity	The driver's log level, read by the USB Tree (0 to 4; 0 off)	2 (fresh install; an update keeps the value there)
XhciLogDebugView	The log sent to DebugView as well	0
XhciInterruptMode	How events arrive: 0 automatic, 1 interrupt line, 2 polling, 3 message-signalled interrupt only	0
XhciSelectiveSuspend	1 suspends idle devices when Windows asks	0
XhciMaxTransferKB	The largest UAS command, 64 to 2048 KiB	1024
XhciForceBulkOnly	1 uses Bulk-Only instead of UAS	0 (1 if the value is absent)
XhciIntelPortSwitch	Intel 7/8/9-series port switchover: 1 on, 2 any Intel controller at your own risk (tools\portsw\)	0
XhciCmMode	Thunderbolt/USB4: 0 off, 1 automatic (2 and 3 are at your own risk)	1
XhciCmApprove	1 approves every device, 0 none (see approval)	1
XhciCmSafeEject	1 offers tunnelled devices for safe removal (98 SE and ME: in the USB Tree and INSTALL /eject only)	1
XhciCmBridgeNumbering	98 SE and ME: 1 sets up PCI bridges behind a tunnel plugged in after start (else Code 29 until restart)	1
XhciCmLogVerbosity	The Thunderbolt driver's log level, read by the USB Tree (0 to 4)	2
XhciCmLogDebugView	The Thunderbolt driver's log sent to DebugView as well	0

docs/using/tuning.md has every value of both drivers, its range and its effect, including polling periods, interrupt moderation, controller-fault handling, the per-controller fixes, the Linux-derived controller quirks and the XhciCm* values; the release notes describe the XhciCm* values in full.

What is tested, and what is not

• Windows 98 SE and Windows 2000 SP4 are the primary targets.
• Real hardware: Windows 98 SE on the ThinkPad E460 and P14s Gen 1, and the Intel port switchover under Windows 98 SE on the Lenovo B490; Windows XP x64 and 7 x64 on the Dell Latitude E7250.
• Every other target, Windows 2000 included, has run in QEMU virtual machines only.
• The free USB class drivers a download may carry are tested in their own project: which of their tests used an emulated device, a real device through a virtual machine, or a real PC is in usb-wdm-free's "Tested by the author".
• Per-system detail: the release notes' Targets and their standing. The test devices: test-equipment.md.

Machine	Controller	Tested by
2012 Lenovo B490	Intel Ivy Bridge, Panther Point HM77 (7-series) PCH, with EHCI beside it. xHCI 1.0.	Me
2015 Dell Latitude E7250	Intel Broadwell-U, Wildcat Point-LP (9-series) PCH, with EHCI beside it. xHCI 1.0.	Me
2016 ThinkPad E460	Intel Skylake, Sunrise Point-LP (100-series) PCH. xHCI 1.0.	Me
2018 HP EliteBook 850 G5	Intel Sunrise Point-LP (8086:9D2F, the E460's controller), xHCI 1.0.	Community
2020 ThinkPad P14s Gen 1	Intel Comet Lake PCH-LP (400-series). xHCI 1.1.	Me
Omores' Intel and AMD desktops	H110, B360, B550, X570, X670	Omores (1.x.x.x)

The package

Install from release-x86\ (32-bit Windows) or release-x64\ (64-bit Windows).

Path	Contents
release-x86\, release-x64\	The drivers to install (below)
debug-x86\, debug-x64\	The same drivers built for troubleshooting; install only if asked
SETUP.EXE	The installer: double-click it to install or update
USBDRV\	Other USB drivers the download carries: NUSB33\, plus FREE\ in the -free download, and FREE\ and NONFREE\ in the -nonfree one (Downloads)
INSTALL.BAT, tools\xhciinst\	For command-line and scripted installs (tools\xhciinst\readme.txt is the reference), and the programs both run (XHCIWIZ.EXE, XHCIWZ64.EXE, XHCIINST.EXE, XHCIIN64.EXE)
tools\xhcitr\	The xHCI98 USB Tree, also the driver's log and snapshot reader
tools\xhciqual\	DOS: XHCIQUAL.EXE and QUALREP.BAT
tools\portsw\	portsw.vbs, portsw-on.bat, portsw-off.bat: the Intel port switchover
tools\silent\	98 SE and ME: the silent install's list and switch
tools\xhcicln\	XHCICLN.EXE, XHCICL64.EXE: optionally lists, and on 2000 to 7 removes, old XHCI98\ entries left by an update from 2.3.x or earlier; nothing needs it
readme.txt	The release notes in plain text

Each driver directory holds:

• xhci98.sys/.inf (controller), xhciuas.sys/.inf (UAS storage), xhcicm.sys/.inf (Thunderbolt and USB4; its PCI-port filter for 2000 to 7, xhcicmf.inf, in nt\ in the x86 directories and beside them in the x64 ones)
• xhcihlpr.sys (32-bit only): a helper 32-bit 2000, XP, Vista and 7 use for a finer timer while polling and, on Vista and 7, a message-signalled interrupt. 98 SE and ME ignore it.
• txtsetup.oem: for F6 during Windows 2000 or XP Setup
• xhci98-test.cer (64-bit only): the public half of the x64 drivers' test certificate; no need to import it
• *.cat (64-bit only): a test-signed catalog for each driver, which 64-bit 8, 8.1 and 10 need
• stor98* files (release- only): the bundled NVMe driver (see NVMe drives), and S98VSD.VXD beside them in release-x86\ for 98 SE and ME

Reporting a bug

Bugs in the free USB class drivers go to usb-wdm-free's issues. The non-free drivers are from their manufacturers, as released, unchanged by this project. Everything else: open a bug report and attach:

• The DOS report: run QUALREP.BAT from real DOS in TOOLS\XHCIQUAL\ and attach the .LOG it names (read-only). If a maintainer asks for the full run, XHCIQUAL --no-page --log FULL.LOG resets the controller and its ports: use a PS/2 keyboard, and do not write the log to a drive on that controller.
• The driver's report: make the problem happen, then in the xHCI98 USB Tree use File > Save Report (or XHCITR /report <file>) and attach the .TXT. It needs the logging level at 2 or more (the default; View > Logging level...).
• An install problem: XHCIINST.LOG from the root of the system drive.

Known limitations/issues

The release notes' Known limitations, Thunderbolt and USB4 limitations and Untested ground have the full lists. The ones most likely to matter:

• Windows 98 SE and ME
  • Stock Windows 98 SE has no USB storage driver without NUSB. HID and audio still work.
  • The first time an NVMe enclosure is plugged in, Windows' wizard may ask for the "Stor98 Storage Controller Disk". Point it at C:\XHCI98.
  • Windows ME: do not unplug a device while Windows is installing it. Shut Down can hang with a USB disk not opened since start; open it once (a dir is enough) or remove it first. (Both happen on Microsoft's own USB stack too.)
  • Windows ME: a UAS drive plugged in before any ordinary stick shows Code 2. Plug in a stick once, then replug the UAS drive.
  • The free and non-free drivers are copied, not staged: point the hardware wizard at the package's folder under C:\XHCI98\USBDRV\.
  • Windows 98 SE: the first USB audio device plugged in after a boot (a webcam with a microphone included) can freeze Windows, with Windows' own drivers too. Plug it in before switching on and leave it plugged in; for a webcam whose microphone you do not need, usb-wdm-free's NOAUD98.INF avoids it.
  • Windows 98 SE and ME: the Sound Blaster X4 needs the free UAC 2.0 driver installed by hand. The free drivers are only copied there, so Windows' own USB audio driver (USB Audio Class 1.0 only) takes the X4 at its first plug and stops Windows with a fatal exception 0E in USBAUDIO. Unplug it and restart (Safe Mode if needed), then Update Driver on its audio entry -> "Display a list of all the drivers in a specific location" -> Have Disk -> C:\XHCI98\USBDRV\FREE\audio\uac2\w98se-me, and restart with it plugged in.
  • Windows 98 SE and ME: installing the free audio or MIDI driver, Windows may ask for wdmaudio.cat, ks.cat and other files of its own from the Windows CD. Point it at the CD's WIN98 folder, or click Skip File for the .cat files: they only hold signatures, which 98 SE and ME do not check.
• Windows 2000
  • A mounted USB drive can come back at Code 31 after a controller recovery or hibernation. Replug it, or disable and enable it.
• Windows XP
  • Installing XP from the F6 floppy needs a PS/2 or built-in keyboard to answer GUI-mode Setup's unsigned-driver question. Windows 2000 does not ask.
• Vista x64 and 7 x64
  • Test-signing mode or F8 is needed at every start; otherwise the controller sits at Code 39 (Vista) or Code 52 (7).
• Windows 8, 8.1 and 10
  • Secure Boot must be off, and the x64 editions need test-signing mode.
  • The uninstall may need a restart and a second run to finish on 8.1 and 10.
• Thunderbolt and USB4
  • Standby and hibernation with a device attached are not supported. Stop and unplug the device first.
  • A drive attached during the install or update appears in Safely Remove Hardware only after a restart or a replug.
  • Windows 2000 to 7 with a USB4 host: ejecting a dock, or an enclosure with its own PCIe switch, stops it safely, but its connection stays up until you physically disconnect it.
  • A dual-mode NVMe enclosure (USB4 or Thunderbolt, and USB) may come up as a USB (UAS) disk instead. Unplug it and plug it in again to get the Thunderbolt or USB4 connection.
• Controllers
  • Disabling a controller the driver had to close off hangs (very rare). Restart instead.
  • Intel 7-series (8086:1E31): too many periodic devices at once (audio, mice) may lose data instead of being refused.
• Untested
  • SuperSpeedPlus (USB 3.2 Gen 2, Gen 1x2 and Gen 2x2): supported, but checked only in an emulator, not on real hardware.
  • SuperSpeed isochronous, polling above 1000 Hz, controllers below xHCI 1.0 (accepted by default; XhciAccept096 0 refuses them), and the Linux-derived controller quirks.

Toolchain and building

The drivers are C89 (no C++ or CRT), built on Windows 11 x64. The toolchain unpacks inside the repository (tools/, git-ignored), installs nothing to C:\, and every script finds it relative to itself.

1. Download into tools\ under these exact names:

   File	Source
   tools\MSVC600.zip	MSVC 6.0 - itsmattkc/MSVC600
   tools\WIN2KDDK.EXE	Windows 2000 DDK - KunYi/WDK_DDKArchive

   The 64-bit build (and the 32-bit xhcihlpr.sys) also needs WDK 7.1 (7600.16385.1) unpacked to tools\WinDDK71.

2. Unpack them in place:

   powershell -ExecutionPolicy Bypass -File scripts\setup-msvc6.ps1        # -> tools\MSVC600
   powershell -ExecutionPolicy Bypass -File scripts\install-w2kddk-cabs.ps1 # -> tools\ntddk

3. Build. both (default) is the shipping release and debug flavours; all adds the emulator-only qemu flavour, which is never published. -amd64 builds the separate 64-bit binaries. Every build runs the gates' self-tests, the host unit tests and the INF, import and charset gates, and stops on any failure.

   scripts\build-driver.cmd both
   scripts\build-driver.cmd both -amd64
   

   The same runs build and gate Stor98, the bundled NVMe driver, from src\stor98 (it also needs the Windows 98 DDK's SCSI.H and SRB.H in tools\w98ddk\inc; src/stor98/docs/BUILD.md); scripts\build-all.cmd runs both architectures at once.

4. The tools build with their own build.cmd in xhciqual\ (needs Open Watcom 2.0 at C:\WATCOM), xhcicln\, xhciinst\ and xhcitr\.

5. Install media: scripts\package\make-package.ps1 (to out\); a release cut: scripts\package\make-release.ps1. Never hand-copy a .sys without its INF.

6. Test in QEMU with qemu-xhci (Win98 SE, Win2000 SP4 and an SMP Win2000 guest; usb-storage and usb-uas for SuperSpeed and UAS).

The version lives in src/xhci_version.h. build-and-test.md has the full procedure (VMs, gates, versioning, packaging), and source-files.md says what each source file is.

Repository Layout

src/            xhci98.sys (C), its two INFs and DDK build files
  uas/          xhciuas.sys, the UAS class driver
  cm/           xhcicm.sys, the Thunderbolt and USB4 driver
  stor98/       Stor98, the bundled NVMe driver (BSD-3-Clause)
test/           Host-side unit tests (test\run-host-tests.cmd)
scripts/        Build wrapper, setup helpers, gates, vm-matrix/
xhciqual/       DOS hardware-qualification tool (Open Watcom)
xhcicln/        Optional cleanup tool for old XHCI98\ devnodes
xhciinst/       Install/update/uninstall tool and INSTALL.BAT
xhcitr/         The xHCI98 USB Tree
docs/           Documentation, indexed by docs/README.md
releases/       Every release cut, one directory per version
images/         Pictures used by this README
.github/        Issue forms
AGENTS.md       Maintainer and AI agent guide
tools/ external/ vm/ out/   Toolchain, reference mirrors, guests, staged media (git-ignored)

Documentation

Everything is under docs/, indexed by docs/README.md. Start with:

• Users: Release notes, Tuning, Release acceptance test, Release history
• Contributors: AGENTS.md (the orientation), Build and test, the roadmaps for 2.0.0.0 onward and for 3.0.0.0 onward, Design records (the HCD is 13; Thunderbolt and USB4 are 21 and 22), Source files, Failure diagnosis and lessons, Test equipment, Legal and provenance record
• Hardware and Windows: xHCI programming, xHCI data structures, Windows 98/2000 WDM constraints, and the 1.x miniport's USBPORT interface and ABI

AI usage

This project was developed with substantial help from AI coding agents:

• Claude Fable 5.1 for planning
• Claude Opus 5.5 for coding
• Codex GPT 6 Astra as an adversarial reviewer

The agents wrote and revised code, tests and documentation under the guidance in AGENTS.md.

Kheng Meng directed the work, ran the hardware validation on real machines and reviewed what went in.

References

• xHCI specification (Intel), citations verified against revision 1.2c
• USB 3.2 specification (USB-IF), revision 1.1 (June 2022) with its ECNs, cited as USB 3.2 p.N
• USB-IF xHCI backwards compatibility testing (v1.7)
• How does USB stack enumerate a device? (Microsoft USB blog) - the hub driver's enumeration steps and timeouts, which the first-enumeration wait's defaults follow
• ReactOS usbport - the usbport.sys miniport interface of the 1.x driver (undocumented by Microsoft)
• Linux xhci-pci.c - controller quirk table
• Haiku XHCI driver and FreeBSD xhci.c - second opinions on hardware details

None of these PDFs is tracked here; fetch your own into the git-ignored docs/references/ (docs/references/README.md has versions and SHA-256 sums). Source mirrors go in external/ (external/README.md).

Licensing and provenance

This project's own source is licensed under the GNU General Public License, version 2 (LICENSE), GPL-2.0-only.

Apart from Stor98's earlier released builds under src/stor98/releases/ (below), the repository tracks no third-party binary on its own, although the tool executables it tracks under releases/ carry statically linked third-party runtimes:

• xhci98.sys and xhciuas.sys link no runtime or extender. The 32-bit builds link no third-party object either; the 64-bit builds, linked by WDK 7.1, carry that kit's /GS stack-cookie handler (__security_check_cookie / __report_gsfailure), which nothing in this project's source calls.
• Some files of xhcicm.sys's source, under src/cm/, are adapted from the usb4-emu project (some lifted from its tools/usb4cm under its earlier MIT licence) and from Linux's drivers/thunderbolt, and keep their copyright lines and licence notices. The legal and provenance record, section 2a, lists each file.
• XHCIQUAL.EXE embeds the Open Watcom runtime and the DOS/32A extender.
• XHCISNAP.EXE, in the releases up to 3.0.0.0, embeds the MSVC 6.0 runtime.
• XHCICLN.EXE, XHCIINST.EXE and XHCITR.EXE embed the MSVC 6.0 runtime; XHCICL64.EXE, XHCIIN64.EXE and XHCITR64.EXE the WDK 7.1 one. None of them contains or runs a Microsoft setup program such as devcon: they call the setup routines of the Windows they run on.

Each tool ships with a NOTICE.TXT recording it, and the LICENSE scope note says that those runtimes carry their own terms and are outside the grant. Neither quotes the terms themselves.

The release download's release-x86\ and release-x64\ carry Stor98, built from this repository's src/stor98/ with the drivers, under its own licence; its LICENSE and NOTICE ship beside it as stor98-LICENSE.txt and stor98-NOTICE.txt. Since 2026-10-19 Stor98 itself - its source and its earlier released builds - is in this repository as src/stor98/, under its own licence (src/stor98/LICENSE, BSD-3-Clause) with its NOTICE recording where its code came from.

This repository carries no Microsoft file. usbd.sys and usbui.dll are the OS's own, copied by Windows Setup from its own install source. The release download may carry one set: NUSB 3.3's seven Windows 98 SE storage files (Microsoft's, apart from USBU2A.SYS), unmodified, from the separate driver-pack repository usb-wdm-nonfree, in a folder of their own with that pack's NOTICE.md, never committed here. They are not this project's work and no licence to redistribute them has been established; a download built without them says so in its readme.txt. On Windows 98 SE, xhciuas.inf names USBNTMAP.SYS as a filter on the UAS device.

In the -nonfree download, USBDRV\NONFREE\ also holds two Microsoft files, the KMDF co-installers ASIX ships with its drivers (WdfCoInstaller01007.dll and WdfCoInstaller01009.dll), unmodified; no licence to redistribute them has been established either.

The full inventory, provenance methods and redistribution boundaries are in docs/contributing/legal-provenance.md, which states facts, not legal conclusions.

Contributions

• Stor98, the bundled NVMe driver, is a fork of SweetLow's nvme9x / nvment, SweetLow's port to Windows 9x and NT4 of nvme2k by Dominik Behr (techomancer). Its README and NOTICE give the lineage and the licence.
• The Windows 98 SE USB storage files in the release download are taken unmodified from the NUSB (Native USB) project's 3.3 release by Maximus Decim; the files themselves are Microsoft's, apart from USBU2A.SYS (see "Licensing and provenance").