The Files-11 structure
creates a set of nondeletable reserved files when a volume or volume
set is initialized. These files control the organization of a Files-11
disk. A Files-11 structure resides on a volume, which is a physical
medium such as a disk pack. A Files-11 volume is an ordered set
of 512-byte blocks. The blocks are numbered consecutively from 0
to n--1; the value of n--1 is the size of the disk in blocks.
File
Identification (FID) Each file
on a Files-11 disk is identified by a unique, system-assigned file
identification (FID) and can have a user-assigned alphanumeric name.
The primary function of a Files-11 directory is to associate the user-assigned
alphanumeric name of each file with the unique FID of the file.
This association ensures that files present on a volume are retrievable
by name.
The FID of a file
consists of a set of three numbers. The first is the file
number (NUM). The file system uses this number as an
offset into the index file (reserved file INDEXF.SYS), which stores
information for all files on a volume.
The
second part of the FID is the file sequence number (SEQ),
which represents the number of times a particular file number has
been used. File numbers are allocated and deallocated as files are
created and deleted. As a result, the file number alone cannot uniquely
identify the file. By incrementing the sequence number each time
a file number is used, the file system ensures that each file has
a unique identification in INDEXF.SYS.
The
third number in the FID is the relative volume number (RVN).
This number indicates the volume (of a volume set) on which the
file resides (ODS--2 only). If the volume set consists of a single
volume, the RVN of all files on that volume is 0.
ODS Directory Hierarchies The Files-11
ODS--2 structure is a multilevel directory hierarchy. The top level
of the directory structure is the master file directory (MFD). The
MFD of a volume is always named [000000]. The MFD contains all top-level
directories, including itself, and reserved files.
A directory is a file that contains other files. A file contained
in a directory can also be a directory and contain other files.
By nesting directories, users can construct directory hierarchies
up to nine levels deep (including the master file directory).
In a volume set, the MFD for all of the user directories on
the volume set is located on relative volume 1. The entries of this
MFD point to directories located on any volume in the set. These
directories in turn point to files and subdirectories on any volume
in the set. The MFD of any remaining volume in the set includes
only the names of the reserved files for that volume.
On
VAX systems, the Files-11 ODS--1 structure supports a two-level
directory hierarchy. Each user identification code (UIC) is associated
with a user file directory (UFD). Each
UFD is included in the MFD of the volume.
HP OpenVMS System Manager's Manual, Volume 2:... 
Files-11 Disk Structure
