What does "Legacy USB Mouse" support in a BIOS mean?
As I understand it, it's not the Mouse or Keyboard that's legacy (PS/2 hasn't changed, USB is backwards compatible with other USB versions), it's the Operating System - legacy mouse mode emulates a PS/2 or AT device when a USB mouse is used with a OS that doesn't support it.
Not the best source, but this seems to confirm that, as does the last post here.
From Platform Compatibility for USB Boot Devices on the Windows Hardware Development Center on MSDN:
Architecture of Legacy Support with Both USB and PS/2 Support
Legacy support is shown in Figure 1 for both USB and PS/2-compatibile support. Important features include:
The BIOS traps events from the USB keyboard and mouse and presents them to the system as PS/2-compatible devices.
The legacy operating system recognizes the USB keyboard and USB mouse as PS/2-compatible devices, with limitations imposed by the USB boot protocol.
Figure 1. Architecture for Legacy Support for USB and PS/2
I found a great explanation:
In a nutshell, legacy is a reroute of USB keyboard and/or mouse to allow an OS to use same. XP does not need legacy support of a USB keyboard or mouse.
An example of where legacy support is required of a USB keyboard is real mode msdos. And, a USB mouse would be addressed as a standard PS/2 mouse in msdos using its mouse driver with legacy support enabled.
http://help.wugnet.com/windows/USB-Legacy-BIOS-ftopict606120.html
As an aside:
I disabled this setting on an Asus P5KPL-CM motherboard (following a suggestion it might be adding to boot time for this board) & am running XP Pro.
When I then attempted to flash the bios via usb flash drive (as this board is capable of doing), this drive was not detected at boot. It was, however, detected by the OS once booted to XP.
I re-enabled "legacy usb", rebooted, and the drive was then detected in bios, allowing me to successfully browse the usb drive & flash the bios.
Therefore, the legacy setting can affect usb detection in bios.
FYI. Cheers from AU!