Node: The node component identifies a particular node in a DECnet network. If the node is omitted, the local node is assumed.

Device: The device component specified the disk or tape on which the file resides. If it is omitted, the device containing the working directory is assumed.

Directory: The directory component specifies a file catalog on the device, the catalog containing the desired file. Multiple catalogs are allowed on some devices. If the directory component is omitted, the working directory is assumed.

Name: The name component, along with the type component identifies a particular file in a chosen directory.

Type: The type component is used to identify the type of file that is being pointed.

Version: This is the best part of VAX VMS. Multiple versions of the same file can exist in the same directory. If a version number is not specified the latest version is taken by default.

Two directories are of notable importance to a VMS user. When a user logs in to VMS, one particular directory is established as the user's login directory or home directory. This directory acts as the repository for the user's files, and the user can create subdirectories under the login directory for additional files. At any time during a VMS session, one directory not necessarily the login directory, is chosen as the default directory. When a file is accessed using a file spec that does not include a device and directory, the file is assumed to reside in a default directory. One can change the default directory by sing the command SET DEFAULT.

Logical Names

A logical name is a named entity that stands for a part or all of a file specification. The primary purpose of a logical name is to relieve the VMS user from having to remember the disk and directory location of a file.

A logical name is created and assigned a value with the DEFINE command. The DEFINE command requires a logical name and its corresponding value:

$ DEFINE DAT_FILES USERDISK2:[JONES.DATA]

Once this command is encountered the value of DAT_FILES will be treated as USERDISK2:[JONES.DATA] until the value of DAT_FILES is superceded with some other logical definition. To deassign a logical name we use the DEASSIGN command. For eg: to deassign DAT_FILES we use the command:

DEASSIGN DAT_FILES

  

User Identification Code

The User Identification Code (UIC) is assigned to certain objects to identify the owner of the object. A file is assigned to an owner when it's created. A UIC is also assigned to each authorized user of a VMS system. Every VMS process has a UIC associated with it.