Abstract: A character generator uses a first memory having a permanent resident area and an overlay area. A second memory stores patterns of all characters. The permanent resident area stores character patterns having the highest frequency of use. The overlay area is not permanent and stores a subset of character patterns known to have high frequency use, but of lesser frequency than in the permanent area. A directory is provided for accessing character patterns in the overlay area. Characters are accessed using character code points. Each character code point represented in the directory has a usage count field and an address pointer field for enabling the character to be chained in a logical sequence with the other characters in accordance with their respective frequencies of use. The directory is searched serially and the search time will be shorter for the characters having highest frequency of use. The characters are accessed in the directory by their code points.

Abstract: Multiple virtual images are built on a display screen of a text processing system by a display access method (DAM) program running interrupt identified service programs. Each of the service programs is provided with stack memory elements for retaining data to run the program. Each of the service programs is run by the DAM program in accordance with priority interrupts with a higher priority interrupt having immediate access to the DAM program. A service program having a low priority interrupt that is being run by the DAM program will be stopped by the occurrence of a higher priority interrupt with the data and address information of the interrupted program retained in the stack memory elements. The service program of the higher priority interrupt is then run and when ended the DAM program retrieves the data for the lower priority program to return to the point of interruption. This program of the lower priority interrupt is then run to an end if not again interrupted by a higher priority interrupt.

Abstract: A cathode ray tube display system is provided for displaying alphanumeric characters which are cyclically refreshed in the sequence of selected positions. The system has conventional means for moving the CRT beam through an arbitrary sequence of selected positions with reference to first and second coordinate axes, in response to position signals, and character defining means for deflecting the beam at each selected position within which a selected character may be defined and in response to signal representations of said selected character for modulating the beam intensity along said pattern to define the character.The system further includes storage means for sequentially storing a coded representation of the character selected to be displayed as well as tab codes and carriage return codes for said displayed characters.