Abstract: In a unified bus data processing system, a memory expansion unit is connected to the bus to convert bus addresses into addresses in a physical memory which may be many times larger than the maximum size that the bus would have been capable of addressing previously. Thus, the memory expansion unit provides directly addressable memory locations which serve to expand the range of physical addresses allocated to the bus by selectively connecting a plurality of expansion memory units to said bus. The memory expansion unit is programmed to convert groups of bus addresses into the same size group of addresses anywhere in physical memory. Until the memory expansion unit is programmed, physical memory is directly addressable by the central processing unit by applying the appropriate bus address and the normal control signals thereto.

Abstract: A video display terminal is disclosed for use in displaying images of data characters on a display screen with modifications to the video characteristics thereof. Coded data characters are provided which represent images to be displayed. Associated with each data character is a coded enhancement character representing a video modification or enhancement to be made to the video image of the associated data character. Video signals are provided for forming the image represented by a data character. These video signals are modified by the enhancement represented by the associated enhancement character and the modified video signal is employed for forming the video image of the data character along with the video enhancement thereto.

Abstract: The system includes a host computer having mass storage facilities together with a plurality of video display terminals having editing capabilities. Facilities are provided so that each editing terminal may on power-up communicate with the host computer which then downloads a control program into the terminal and is stored in the terminal's main memory such as read/write random access memory (RAM). Data to be displayed at the terminal may be downloaded from the host computer in the same manner and, in addition, data may be entered by a local keyboard for display and editing purposes. Each terminal is a processor driven terminal with a common bus architecture and performs various functions in accordance with the control program downloaded from the host computer. The terminal is structured so that it may display text obtained from one or more input sources on different areas of a common display screen. The text in the different areas may be scrolled and edited independently of each other.