This application note describes how to implement a design where a single ATA/ATAPI device is shared by the SMSC USB2005 USB ATA/ATAPI controller and a second ATA/ATAPI Controller. The second ATA/ATAPI controller is referred to as ATAC in this application note. One application where two ATA/ATAPI controllers are needed is for example an USB MP3 player where the SMSC USB2005 performs data transfer between media and an USB host. The ATAC performs the audio procession. Another example is an external hard drive that supports both USB and Ethernet or IEEE 1394 connectivity.