storage (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/O parallelism but made crash recovery expensive.

NSS redesigned the lower levels of the file system,

introducing the concepts of logical volume and physicalvolume 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.