This means the BIOS must be capable of handling a maximum length descriptor if such a descriptor is returned. However, the BIOS is only required to configure boot devices. Nonboot devices can be left in the addressed USB visible device state. To ensure fast boot times, the USB keyboard and mouse should be connected directly to a USB root port or at the first layer of a USB hub in the preinstalled system configuration. Enumerating boot devices on layers beyond a USB hub significantly impacts boot time.
Interrupt handlers preserve values in all registers.
The values of the other bits in the flags register must be preserved unless the API is documented to modify them. Timer is supported at system boot. ACPI legacy-free support is reported. Note that the 8042 flag must be set to 0 for systems that do not include an 8042 controller, and set to 1 in mobile PCs and desktop systems that include the 8042 controller. Debug Port Table in the BIOS, as described in ACPI section 5.2.11.