1. In a computer system providing data access to a plurality of individually replaceable physical data volumes each of which contains at least one directory identifying named and timed data files which are contained in the respective volume with the possibility existing that files with the same name may exist on different ones of said volumes with different time indicia; a method of providing, to a user, an aggregated file listing, said method comprising: generating from said directories respective volume directory tables containing file names and respective media locations where respective file data may be read, said volume directory tables including also a pointer identifying any next predecessor in time file with the same name if extant in the plurality of physical data volumes, and a pointer identifying any next superseding in time file with the same name if extant in the plurality of physical data volumes generating from said directories a path table which provides, for each directory, a logical access path together with a pointer location containing a pointer identifying at least one volume directory table corresponding to a physical volume where the file data may be read, whereby said listing may be updated when an available volume is changed by updating the respective volume directory table and the related pointers in other volume directory tables without accessing all directories.