Here examined are CASIS computer-readable magnetic tapes which are highly evaluation among many computer-readable magnetic tapes on sale, its present system (1401/360 Format) and the new SDF system which will be adopted from the beginning of 1972. The magnetic tapes of the present system, POST-J and CA Condensates are examined as to their utility, problems, future prospects, based on the results of Asahi Chemical Industry Co.'s comparatively large-scaled SDI services using these tapes.