Random Scan Display Device
The original cathode ray tube, developed in the late fifties and early sixties, produced charts and pictures, line through line on the tube surface in any of random order or direction specified, in a vectorial fashion. The e- beam was moved along the exact direction and for the exact length of the line as particular. For this purpose, the kind of device was termed as a Vector, Calligraphic or Stroke as it drew lines just like our ancestors drew letters as pictures, stroke by stroke. The method was the same to a hand-sketch or pen-plot.
The graphics commands are passed on to a display-file program produced by the computer and stored in the refresh storage region or buffer memory. The program is executed one time in all refresh cycle of about 1/30 sec. The e- beam is moved to trace the image line by line through a display processor. All line, if curved or straight is displayed through the activation of exact points among particular end-point via means of vector creators of the digital or analog type, the former being smoother, and the latter being cheaper and faster. Curved lines and text qualities are displayed like a series of short lines or through a sequence of points.