What Is USB Legacy Support In Bios

July 14, 2023 1 By tech

USB legacy support, as the name suggests, refers to the backward compatibility feature provided by BIOS for USB devices. It allows older USB devices, such as keyboards, mice, and printers, to be recognized and used by the computer system. Without USB legacy support, older USB devices may not function correctly or may not be detected by the operating system.

The Importance of USB Legacy Support

USB legacy support is essential because it enables the use of older USB devices with modern computer systems. Many users still have functional older USB devices that they prefer to continue using rather than purchasing newer replacements. USB legacy support ensures that these devices remain compatible and usable with the latest hardware and operating systems.

USB Legacy Support and Compatibility Modes

To facilitate USB legacy support, BIOS offers various compatibility modes that can be configured by the user. These modes determine how USB devices are recognized and operated by the system. Let’s explore some of the common compatibility modes associated with USB legacy support:

1. Auto

The Auto mode, also known as the Default or Enabled mode, automatically detects and enables USB legacy support for devices that require it. This mode is suitable for most users who want a hassle-free experience without manually configuring settings.

2. Enabled

The Enabled mode explicitly enables USB legacy support for all USB devices connected to the computer. This mode ensures maximum compatibility with older devices but may not be necessary if you only use newer USB peripherals.

3. Disabled

The Disabled mode, as the name implies, disables USB legacy support altogether. This mode is suitable if you solely use newer USB devices that do not require legacy support. Disabling USB legacy support can potentially speed up the boot process by skipping the initialization of legacy USB devices.

4. Manual Configuration

Some BIOS implementations allow users to configure USB legacy support on a per-device basis. This granular control enables users to selectively enable or disable legacy support for specific USB devices. It can be useful when you have a mixture of older and newer USB peripherals connected to your computer.

Impact on USB Device Functionality

USB legacy support affects the functionality of USB devices in a few ways. Let’s discuss the key aspects:

1. Device Recognition

With USB legacy support enabled, the BIOS can recognize and identify older USB devices during the boot-up process. This recognition allows the operating system to load the necessary drivers and initialize the devices correctly. Without USB legacy support, the system may fail to recognize older USB peripherals, rendering them unusable.

2. Keyboard and Mouse Functionality

USB legacy support is particularly crucial for older keyboards and mice that use the PS/2 (Personal System/2) protocol. By enabling USB legacy support, these devices can be used seamlessly with modern systems that lack PS/2 ports. This feature ensures that users can continue using their preferred input devices without compatibility issues.

3. Booting from USB Devices

USB legacy support also plays a vital role in booting from USB devices. By enabling USB legacy support, the BIOS can treat USB storage devices as bootable devices, allowing you to install or boot an operating system from a USB drive. This feature is especially useful when installing a fresh operating system or troubleshooting existing installations.

Why Would I Need Legacy USB Support?

You might need Legacy USB Support if you’re using an older operating system that doesn’t understand how to use USB devices. For example, MS-DOS, an old operating system, doesn’t know how to use USB keyboards or mice. But with Legacy USB Support turned on, you can use a USB keyboard or mouse with MS-DOS, and it will think it’s using a PS/2 device.

Does Legacy USB Support Affect the Speed of My USB Ports?

No, Legacy USB Support doesn’t affect the speed of your USB ports. Whether your USB ports are version 1.1 or 2.0 (these are different versions of USB technology that offer different speeds), Legacy USB Support doesn’t change this. It only helps your computer use USB devices as if they were PS/2 devices.

Is it Safe to Disable USB Legacy Support in BIOS?

Whether it is safe or not to disable USB Legacy Support in BIOS depends on your specific needs and system configuration. Here are some considerations:

Accessibility to BIOS and bootloaderWith USB Legacy Support disabled, you may not be able to use USB keyboards or mice to access the BIOS settings or perform actions in the bootloader menu.
USB boot functionalityDisabling USB Legacy Support can cause USB boot functionality to stop working.
Compatibility with older USB devicesUSB Legacy Support is designed to provide compatibility for older USB devices that may not have native support in modern systems. Disabling it may prevent these older devices from functioning properly or being recognized.
Operating system supportDisabling USB Legacy Support typically does not affect USB usage within the operating system itself3. However, some older operating systems or specific software may rely on USB Legacy Support for certain functionalities.

Important: Always consult your system documentation or manufacturer’s recommendations before making any changes to the BIOS settings.

How to Enable USB Legacy Support in BIOS

USB Legacy Support Bios

To enable USB Legacy Support in BIOS, follow these steps:

  1. Restart your computer and enter the BIOS setup by pressing the appropriate key during startup. The key to enter the BIOS setup varies depending on the manufacturer, but it is usually F2, F10, or Delete.
  2. Once you are in the BIOS setup, navigate to the “Advanced” or “Integrated Peripherals” menu using the arrow keys.
  3. Look for an option called “USB Legacy Support” or “USB Keyboard/Mouse Support” and select it.
  4. Change the setting to “Enabled” or “On” using the arrow keys.
  5. Save the changes and exit the BIOS setup by pressing the appropriate key. The key to save and exit the BIOS setup varies depending on the manufacturer, but it is usually F10.

Note: Enabling USB Legacy Support may reroute the USB keyboard and/or mouse to allow an operating system to use them. It is not needed for newer systems that have native USB support. Disabling USB Legacy Support may prevent some older USB devices from working.

Compatible Devices with USB Legacy Mode

Devices that are compatible with USB Legacy Mode include:

  • PS/2 or AT keyboards
  • PS/2 or RS-232 mice
  • Some SATA disk controllers

Note: USB Legacy Mode is designed for legacy systems or systems that lack native support for USB devices. It allows these older devices to function in an operating environment that is not USB aware. However, newer systems with native USB support may not require USB Legacy Mode to be enabled.

Common Issues with USB Legacy Support in BIOS

Some common issues with USB Legacy Support in BIOS include:

  • System crashes: Enabling Legacy Support can sometimes cause system crashes, especially if AMD64 64-bit mode is enabled. This is because the SMM BIOS isn’t expecting the CPU to be in 64-bit mode.
  • Compatibility issues: Disabling USB Legacy Support may prevent some older USB devices from working. Enabling it may be necessary for the system to recognize and boot from a USB device.
  • Performance issues: Enabling Legacy Support can potentially decrease system performance by allocating system resources less efficiently. Disabling it can potentially improve system performance.
  • BIOS updates: Some BIOS updates may disable Legacy Support by default, causing compatibility issues with older USB devices.
  • Dual-mode devices: Enabling Legacy Support allows the use of dual-mode devices in USB ports, which can be beneficial if you have devices that support both USB and PS/2 interfaces. Disabling it may result in the inability to use these devices properly.

Note: USB Legacy Support is primarily intended for legacy systems or systems without native USB support. Newer systems with native USB support may not require USB Legacy Support to be enabled. Disabling USB Legacy Support may prevent some older USB devices from working.

xHCI and USB Legacy Support

The correlation between xHCI and USB Legacy Support lies in their compatibility and interdependency. While xHCI represents the latest and most advanced USB host controller interface, USB Legacy Support ensures backward compatibility with older USB devices. Together, they form a cohesive system that allows users to connect and utilize a wide range of USB devices seamlessly.

When a computer system is equipped with xHCI, it typically enables USB Legacy Support by default. This ensures that users can connect to older USB devices without encountering compatibility problems. However, in some cases, certain issues may arise due to conflicts between xHCI and USB Legacy Support.


USB legacy support in BIOS is a critical feature that ensures backward compatibility for older USB devices. It allows these devices to be recognized, used, and configured correctly by modern computer systems. Whether you have an older keyboard, mouse, or printer, USB legacy support ensures their continued functionality and compatibility.

By understanding USB legacy support and its impact on USB device functionality, you can make informed decisions when configuring your BIOS settings. Remember to choose the appropriate compatibility mode based on your specific needs and the USB devices you use.

Next time you encounter USB legacy support in your computer’s BIOS settings, you’ll have a solid understanding of what it entails and how it affects your hardware. With this knowledge, you can make the most out of your USB devices while embracing the advancements of modern computing.


Why is USB legacy support important?

USB legacy support is important because it enables the use of older USB devices with modern computer systems, ensuring that they remain compatible and functional.

Does USB legacy support affect keyboard and mouse functionality?

Absolutely. Enabling USB legacy support in the BIOS allows USB storage devices to be treated as bootable devices, enabling users to install or boot an operating system from a USB drive.

How can USB legacy support benefit users with older peripherals?

USB legacy support ensures that users can continue using their preferred older USB devices without compatibility issues, as it enables the devices to function correctly with modern computer systems.