Usb-FDD has been eliminated. But when you install the system on the old machine, you will find it. The previous machine did not have an optical drive and did not support USB-HDD. There is only USB-FDD, so you must not use USB-FDD.
FDD mode means that USB flash drive is simulated as floppy drive mode. After the USB flash drive is started, the computer will treat the USB flash drive as a floppy disk. Therefore, the drive letter displayed on the command line is a:. U disk in this mode can't be found when it is started on some machines that support USB-FDD startup. Please use it as appropriate.
USB hardware structure
USB uses four-wire cables, two of which are serial channels to transmit data, and the other two provide power for downstream devices. For any peripheral that has been successfully connected and identified with each other, data will be transmitted at the highest rate that both devices can support.
The USB bus will automatically switch from high speed to low speed in compatible transmission mode according to the peripheral conditions, and the matching will be locked at an appropriate rate. USB is a token-based bus. Similar to token ring network or FDDI token-based bus. The USB host controller broadcasts the token, and the device on the bus detects whether the address in the token is consistent with itself, and responds by receiving or sending data to the host.
Reference to the above content: Baidu Encyclopedia -USB-FDD