(Unix File System) The traditional file system used by Unix systems. Also called "Fast File System" (FFS) and "Berkeley FFS," the major difference between UFS and the earlier "FF" versions was to break up the disk into small chunks called "cylinder groups." Each cylinder group contains its own indexes and data blocks in order to prevent excessive disk thrashing on large volumes. UFS and the ext2 file system used in Linux are very similar (see ext2). Numerous proprietary implementations of UFS exist, and Sun added journaling to UFS in Solaris 7 (see journaling file system). See file system.