The file system recognizes two general classes of files:
user-defined files, which you or other users define, create, and make
available for your own purposes
system-defined files, which the file system defines and makes available
to all users to indicate standard input/output devices
These files are distinguished by the file names and other descriptors
(such as group or account names) that reference them, as discussed
below. You may use both the file name and descriptors, in
combination, as either formal designators within your programs or as
actual designators that identify the file to the system. Generally,
however, most programmers use only arbitrary names as formal
designators, and then equate them to appropriate actual file
designators at run time. In such cases, the formal designators (user
file names) contain from one to eight alphanumeric characters,
beginning with a letter; the actual designators include a user or
system file name, optionally followed by a group name, account name,
and/or security lockword, all separated by appropriate delimiters.
This technique facilitates maximum flexibility with respect to file
references.
