Where disk files are used, the grandfather-father-son updating backup concept is relatively difficult to implement because the

(a) location of information points on disks is an extremely time-consuming task.

(b) magnetic fields and other environmental factors cause off-site storage to be impractical.

(c) information must be dumped in the form of hard copy if it is to be reviewed before being used in updating.

(d) process of updating old records is destructive.