Abstract: A central processor holds a word-processing program and an entire document to be processed. A smaller I/O processor, connected to the central processor and to an interactive display, holds code for some functions of the word processor, and holds a part of the document. As an operator performs editing tasks at the display, the I/O processor performs locally those functions involving only the document part it holds. When additional document text is required to complete a function, the central processor performs that part of the function involving the additional text.