File Management - IBM

Chapter 1. Introduction to File Management
File types
Traditional file management, formerly known as data management, is the part of
the operating system that controls the storing and accessing of data by an
application program. The data may be on internal storage (for example, database),
on external media (diskette, tape, printer), or on another system. File management,
then, provides the functions that an application uses in creating and accessing data
on the system and ensures the integrity of the data according to the definitions of
the application.
File management provides functions that allow you to manage files (create, change,
override, or delete) using CL commands, and create and access data through a set
of operations (for example, read, write, open, or close). File management also
provides you with the capability to access external devices and control the use of
their attributes for creating and accessing data.
If you want to make more efficient use of printers and diskette devices, file
management provides the capability of spooling data for input or output. For
example, data being written to a printer can be held on an output queue until the
printer is available for printing.
On the IBM AS/400 system, each file (also called a file object) has a description
that describes the file characteristics and how the data associated with the file is
organized into records, and, in many cases, the fields in the records. Whenever a
file is processed, the operating system (the Operating System/400 or OS/400
program) uses this description.
You can create and access data on the system by using these file objects. File
management defines and controls several different types of files. Each file type has
associated CL commands to create and change the file, and you can also create and
access data through the operations provided by file management.
The file management functions support the following types of files:
v Database files are files (including distributed files) whose associated data is
stored permanently in the system.
v Device files are files that provide access to externally attached devices such as
displays, printers, tapes, diskettes, and other systems that are attached by a
communications line. The device files supported are:
– Display files, which provide access to display devices
– Printer files, which describe the format of printed output
– Tape files, which allow access to data files on tape devices
– Diskette files, which provide access to data files on diskette devices
– Intersystem communications function (OS/400-ICF) files, hereafter referred
to as ICF files, which allow a program on one system to communicate with a
program on the same system or another system
v Save files are files that are used to store saved data on disk (without requiring
diskettes or tapes).
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