Files-11

Files-11, also known as on-disk structure, is the file system used by Digital Equipment Corporation OpenVMS operating system, and also (in a simpler form) by the older RSX-11. It is a hierarchical file system, with support for access control lists, record-oriented I/O, remote network access, and file versioning.

Files-11 is similar to, but significantly more advanced than, the file systems used in previous Digital Equipment Corporation operating systems such as TOPS-20 and RSTS/E.

The native OpenVMS file system is descended from older DEC operating systems and is similar in many ways. A major difference is the layout of directories. These file systems all provided some form of rudimentary non-hierarchical directory structure, typically based on assigning one directory per user account. Under RSTS/E, each user account was represented by two numbers, a [project,programmer] pair, and had one associated directory. Special system files, such as program executables and the OS itself, were stored in the directory of a reserved system account.

While this was suitable for PDP-11 systems, which possessed limited permanent storage capacity, VAX systems with much larger hard drives required a more flexible method of file storage: hierarchical directory layout in particular, the most notable improvement in ODS-2.

They are "similar" because they had the same designer Dave Cutler, originally from Digital Equipment Corporation. Dave later went to Microsoft.

"Files-11" is the general term for five separate file systems, known as on-disk structure (ODS) levels 1 through 5.

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