Extending or truncating a file physically

The physical end-of-file can be changed with the help of the MAP function.

Physical extension of files

When a window is defined with MAP, DIV ensures (for OPEN OUTIN | INOUT, but not INPUT) that disk space is allocated in 4K blocks for the file area that is represented by the window. For window pages that follow the physical end-of-file, DIV allocates space in 4K blocks.

Physical truncation of files

Blocks occupied by a file can be freed with the help of the FILE macro by specifying a negative SPACE value or with the command MODIFY-FILE-ATTRIBUTES ...RELEASE=. Blocks are released up to the last logical 4K page.