Legacy USB Support is a BIOS/UEFI firmware setting that enables USB Human Interface Devices (keyboards, mice) and USB storage devices to function before the operating system loads. Without it, USB devices only work after Windows (or another OS) takes over USB management.
Part 1. What Is Legacy USB Support?
Modern operating systems manage USB devices through their own drivers. But in the period between power-on and OS boot — during BIOS setup, POST, or OS installation — the operating system's USB drivers haven't loaded yet.
Legacy USB Support bridges this gap by having the BIOS emulate older PS/2-style communication (INT 9h and INT 13h) for USB devices, so they work as if they were legacy PS/2 hardware.
| Setting | Effect When Enabled | Effect When Disabled |
|---|---|---|
| Legacy USB Support | USB keyboard/mouse works in BIOS | USB only works after OS loads |
| USB Legacy for Storage | USB drives visible as boot devices | USB storage invisible pre-OS |
| xHCI Hand-off | USB 3.0 devices work in pre-OS | May cause USB 3.0 issues pre-OS |
| EHCI Hand-off | USB 2.0 devices work in pre-OS | May cause USB 2.0 issues pre-OS |
💡 Tip: If your USB keyboard doesn't respond when you press Delete or F2 to enter BIOS, enabling Legacy USB Support is the fix — but you'll need to use a PS/2 keyboard to enable it, or temporarily plug in a PS/2-to-USB adapter.
Part 2. When Should You Enable Legacy USB Support?
Enable Legacy USB Support in these scenarios:
- You need to use a USB keyboard or mouse in BIOS/UEFI setup — without Legacy USB Support, only PS/2 keyboards work pre-OS
- Booting from a USB drive — some older BIOS versions require Legacy USB Support to see USB drives in the boot menu
- Running DOS or legacy OS tools that don't have USB drivers
- Windows/Linux installer is not detecting your USB keyboard during setup
🗣️ r/buildapc user: "I built a new PC and my USB keyboard wouldn't work in BIOS. Plugged in an old PS/2 keyboard, enabled Legacy USB Support, and the USB keyboard immediately started working in BIOS."
Disable Legacy USB Support when:
- You've confirmed all USB devices work normally in BIOS without it
- Some Linux distributions have issues with USB Legacy emulation enabled
- You're troubleshooting USB handoff problems in Windows (xHCI/EHCI-related)
Part 3. How to Enable or Disable Legacy USB Support in BIOS
The exact location varies by motherboard manufacturer, but here are common paths:
Intel/ASUS boards:
- Enter BIOS (Del or F2 at startup)
- Go to Advanced → USB Configuration
- Find Legacy USB Support or USB Legacy
- Set to Enabled or Disabled
- Save and exit (F10)
MSI boards:
- Enter BIOS (Del at startup)
- Go to Settings → Advanced → USB Configuration
- Toggle Legacy USB Support
GIGABYTE boards:
- Enter BIOS (Del at startup)
- Go to Peripherals or USB
- Find Legacy USB support
| Manufacturer | BIOS Entry Key | USB Setting Location |
|---|---|---|
| ASUS | F2 or Del | Advanced → USB Configuration |
| MSI | Del | Settings → Advanced |
| GIGABYTE | Del | Peripherals / USB |
| ASRock | F2 or Del | Advanced → USB Configuration |
| HP | Esc or F10 | Advanced → Device Options |
| Dell | F2 | General → USB Configuration |
💡 Tip: After making any BIOS change, press F10 to save and exit. Exiting without saving (pressing F3 or Escape) will discard your change.
Part 4. Legacy USB Support and USB Boot Drives
Legacy USB Support is often required when booting from a USB drive on older systems. However, modern UEFI systems usually detect USB drives without Legacy USB Support, as long as the USB drive is formatted correctly:
- UEFI boot: USB drive must be formatted as FAT32 with a GPT partition table
- Legacy/CSM boot: USB drive can be FAT32 or NTFS with MBR partition table
If your system won't boot from a USB drive:
- Enter BIOS and ensure Boot from USB is enabled
- Enable Legacy USB Support if the boot menu doesn't show the USB drive
- Check if Secure Boot is blocking a non-signed OS installer — disable it if so
- Confirm the USB was created with the correct tool (e.g., Rufus for Windows)
⚠️ Important: Disabling Secure Boot may allow unsigned operating systems to load. Re-enable it after completing any one-time boot task from an external drive.
🗣️ r/techsupport user: "USB boot wasn't working until I enabled Legacy USB Support AND disabled Secure Boot. Both were needed on my older HP laptop to get the installer running."
Part 5. Recover Files From USB Drives With Ritridata
If you've been troubleshooting USB boot issues and accidentally lost data from a USB drive or external drive — through formatting, deletion, or corruption — Ritridata can recover deleted files from USB drives, external HDDs/SSDs, SD cards, and Windows drives.
Step 1 — Select the drive/location
Step 2 — Run a safe scan
Step 3 — Preview and recover to another drive
FAQ
What does Legacy USB Support do in BIOS? It enables USB keyboards, mice, and storage devices to function before the operating system loads. The BIOS emulates older PS/2-style communication for USB devices during pre-OS stages.
Should Legacy USB Support be enabled or disabled? Enable it if you use a USB keyboard in BIOS or need to boot from a USB drive on older systems. Modern UEFI systems often don't need it for day-to-day use, but it generally doesn't cause harm when enabled.
Does Legacy USB Support affect USB speed? No. Legacy USB Support only affects pre-OS USB device detection. Once Windows loads, USB devices switch to the OS's native drivers and run at normal speeds.
Why won't my USB keyboard work in BIOS? Your BIOS likely has Legacy USB Support disabled. You'll need a PS/2 keyboard (or PS/2-to-USB adapter) to access BIOS settings and enable Legacy USB Support for USB keyboards.
Can enabling Legacy USB Support cause problems in Windows? Rarely. In some configurations, Legacy USB emulation can interfere with USB 3.0 handoff (xHCI). If you notice USB 3.0 issues in Windows, try disabling Legacy USB Support and enabling xHCI Hand-off instead.
What is xHCI Hand-off in BIOS? xHCI Hand-off is a related BIOS setting that manages how USB 3.0 controllers are handed off from BIOS to the OS. Enable it if USB 3.0 devices have issues during OS installation or in operating systems without native xHCI support.
Is Legacy USB Support required for Windows 11 installation? Usually no — Windows 11 installation media supports modern UEFI USB booting natively. However, if the USB drive doesn't appear in the boot menu on older hardware, enabling Legacy USB Support may help.