Abstract: A transaction execution system including at least one transaction terminal in communication with a host data processing system. A transaction at the terminal is authorized based, at least in part, upon correspondence of personal identification data entered by the terminal operator at a keyboard with account identification data read from an account card. When the personal identification data is not derived from the account identification data, the correspondence check is made at the host data processing system by comparison of encrypted identification data with validation data. The host may, upon failure of correspondence, communicate a conditional authorization message to the terminal, which enables the terminal operator to again attempt to enter the correct personal identification data. The host data base stores as validation data encrypted identification data, and only double encrypted identification data appears on the communication lines.

Abstract: Scanned image data is compressed and stored in a central processing unit. An image for display is recalled, decompressed, and then recompressed for refresh storage for a CRT display device. The refresh compressed image is recalled when necessary for display and refresh, and directed through a plurality of parallel operated decompressors and refresh buffers to drive the display unit. An unfilled compressed refresh image store is filled with zeros to complete the display with an all white scan. In an overflow situation, a partition boundary is generated to identify that more data follows. To display the subsequent image, upon request, the overflow increment value which repeats a few scan lines is transmitted and a visual overlap image with subsequent data is compressed for refresh store and display and refreshed as required.