在全双工链路上操作非智能crt终端的一种通常方式，在该方式下，每个键入的字符都是先从目的地（通常为一本地的计算机或终端控制器）被返回来，然后才显示到屏幕上。

• The common method of operating an unintelligent CRT terminal on a full duplex link; each character that is keyed in is returned from the destination(usually a local computer or a terminal control unit) before it is displayed on the screen.