Comentário de @Hennes (pergunta original):
Some background: Most USB devices function in one of two modes: Master or slave. The computer typically is the master and uses and USB-A socket. Slaves usually use the USB-B (square) socket. You cannot connect master to master or slave to slave. (Well, you can with a weird cable, but it will not work). The only exception seems to be some mobile devices which often use a special micro-AB connector which can switch modes. This is what Ali Chen refers to as USB on the go (OTG).