Video Disc and Computer-Based Training

Video discs represent the earliest use of optical storage technology. In contrast to CD-ROM and worm disc their primary purpose is to hold analogue rather than digital data, i.e. the signals to generate a PAL 625-line television display. Data is recorded in the form of pits and lands, the length of the pit indicating the voltage of the signal. It is thus feasible to hold 36 minutes of video on a 12-inch disc — one second of colour video in analogue form requires one megabyte of storage, whereas the same information in digital form would require 30 megabytes. Obviously this also affects the speed of reading and display. Compact discs are expected to be the eventual successors of video disc for multi-media systems, but at the time of writing their data transfer rate is too slow for showing good quality video sequences.