(NSS) A major Multics implementation project during the 1970s. The initial Multics file system deSIgn had evolved from the one-huge-disk world of CTSS. When multiple disk units were used they were just asSIgned increaSIng ranges of disk addresses, so a segment could have pages scattered over all disks on the system. This provided good I/Oparallelism but made crash recovery expenSIve. NSS redeSIgned the lower levels of the file system, introducing the concepts of logical volume and {phySIcal volume} and a mapping from a Multics directory branch to a VTOC entry for each file. The new system had much better recovery performance in exchange for a small space and performance cost. (1997-01-29)