The BIOS switch both adjusts the polling rate and allows you to turn off advanced keyboard features for compatibility with certain motherboard BIOS and KVM switches. Settings of 1, 2, 4, and 8 are millisecond polling rates (1ms = 1000hz). Switching to BIOS reduces the polling rate and turns off other features for maximum compatibility. By default we ship at 1ms (1000Hz) and most gamers will prefer to just use the setting.
If it's a key, my guess it's for accessing the BIOS Setup on the computer it's attached to (but you would need to programme the key to the correct preset first, using the supplied software).
The BIOS switch both adjusts the polling rate and allows you to turn off advanced keyboard features for compatibility with certain motherboard BIOS and KVM switches. Settings of 1, 2, 4, and 8 are millisecond polling rates (1ms = 1000hz). Switching to BIOS reduces the polling rate and turns off other features for maximum compatibility. By default we ship at 1ms (1000Hz) and most gamers will prefer to just use the setting.