EFS

Using EFS, data is encrypted on an NTFS disk, making it pretty hard for someone to bypass the operating system to retrive the information.

Extent File System, SGI's early block-device filesystem, in wide use on their pre-Irix-6.0 workstations. Not to be confused with extfs (latterly, ext2fs), Linux's "Extended- (and Second Extended-) Filesystem".

Irix 6 adds support for a replacement filesystem ("XFS"), which is journalling-capable; since post-6.5 kernels are incapable of mounting EFS volumes read-write, SG's intention appears to be to reserve EFS format for software distribution CDs, presumably because it's useful to have a filesystem format available for this where the index nodes and related file metadata take up a small(er) percentage of the disk.