Files can contain any number of items and automatically expand to any size. A file should be created by determining how many items are stored in it, and the average size of one item. When the file is created, the entire space is allocated out of contiguous disk frames, even though the file is initially empty. This is the minimum amount of disk space the file will ever take up. It can grow but it cannot shrink below this size.
The file is accessed by looking in the account master dictionary and obtaining the base address, or base Frame Identifier (FID). The size of the file in frames is called the modulo. The D3 system uses the account md to keep track of where files are and how much disk space the files use. It uses a file dictionary to keep track of how the data is stored and displayed for each item in the file.
The space allocated remains empty until items are added to the file.
These topics are presented:
Data Input and Output Specifications
File-Defining Item or D-pointer
See Also
Controlling and Dependent Structures