Patent US 4,428,065

A data processing system comprises a first selection device for selecting a plurality of characters of a first set, the characters of the first set each being defined by a bit map of first predetermined dimensions. A second selection device is capable of selecting a plurality of characters of a second set, the characters of the second set each being defined by a bit map of second predetermined dimensions greater than the first predetermined dimensions. A display device is capable of displaying the selected characters of the first and second sets, and a control device is responsive to the first and second selection devices for controlling the display device to display the selected characters of the first set in a first display area and the selected characters of the second set in a second display area, the first dislay area representing a page of text of characters of the first set, and the second display area representing a magnified portion of the page of text comprised of characters of the second set.