The ATEN US221A/ US421A is a 2/4 Port USB 2.0 Peripheral USB Switch that allows up to 2/4 computers to share the use of a single USB peripheral device (such as a printer, scanner, mass storage drive, etc.) on a one-at-a-time basis. The peripheral focus can be given to a computer manually by using pushbuttons on the switch, using the software-based configuration utility or by the Auto Switch function.