This USB 3.0 Switcher Selector allows one button swapping between 2 computers to share 4 USB peripheral devices without constantly swapping cables or set up complicated network sharing software; Ideal for sharing devices such as printer, scanner, mouse, keyboard, card reader, flash drive and other USB deivce between 2 computers; If the switcher doesn't work on external hard disk, please connect the device with Micro USB Cable for extra power.