File areas

Normal data blocks, index blocks, indexed data blocks, free blocks, the control block, and overflow blocks constitute the used area of an ISAM file. The unused file area, by contrast, is that part of a file which the user can release at any time (via the SPACE operand of the FILE macro or MODIFY-FILE-ATTRIBUTES command).

Figure 27: File areas of an ISAM file

Each field in this figure corresponds to one PAM page. Empty fields are PAM pages which have not yet been used by ISAM.

FILE-SIZE	Total size of the ISAM file (here: 18 PAM pages).
Area in use	All blocks which have been used at least once for the file, even if they are now free (here: HIGH-US-PA = 10).
Unused area	Blocks which have not yet been used by ISAM and can be released at any time (here: 8 PAM pages).