Abstract: In a dumb terminal to which an auxiliary device may be attached, improvements in display definitions. In the transfer of data between a host computer and the terminal or an auxiliary device, and in character generation memory. In the area of display definition, pages may be mapped onto the terminal's display memory and viewports may be mapped onto pages. Page and viewport definition are independent of each other and settable modes permit a viewport to follow the active position. In the area of transfer of data, the source of data for the host computer and the destination of data from the host computer may be specified independently. Improvements in flow control ensure that the host computer can always change the destination of data and gain control of the terminal. Improvements in access control ensure that neither the terminal nor the auxiliary device can monopolize transfer between it and the host.