原本的 USB 設備中, 有主-從 (master- slave) 的關係, 如 PC 通常是當作 master, 印表機是 slave. 二個 master 相連, 這二個masters 並不能互通.
符合OTG 規格的裝置不必再去辨認主- 從, 裝置互連就可以溝通. 如: 數位相機, 可以連接 PC (與PC 互傳檔案), 也可以連接印表機, 列印相片.
USB On-The-Go Basics
USB On-The-Go (OTG) allows two USB devices to talk to each other without requiring the services of a personal computer. Although OTG appears to add "peer to peer" connections to USB, it does not. Instead, USB OTG retains the standard USB host/peripheral model, where a single host talks to USB peripherals. OTG introduces the dual-role device (DRD), capable of functioning as either host or peripheral. Part of the magic of OTG is that a host and peripheral can exchange roles if necessary.
Before OTG, the concept of an embedded host was already established in the USB world. Instead of duplicating the full UHCI/OHCI USB controllers and drivers built into personal computers, most embedded host chips provide limited hosting capabilities. This makes them better suited to the embedded environment than to the PC with its huge resources and infinite capacity for drivers and application software
裝置, 譯自 device, 就是指 '那台機器'