Table B (File architecture)

This topic covers the internal architecture of a Model 204 Table B page.

For a discussion of the ways a File Manager may organize these pages in a file, please refer to File Design (File Management).

At a minimum, Table B contains all of the base records in a Model 204 file. If Table X is not enabled it also contains all extension records. If Table E is not enabled, then any data whose contents is greater than 255 bytes must be held as a series of repeating fields.

The structure of a Table B page

Not shown is a 4 byte 'Reuse Queue Page Number' for Unordered Files. If it is present, it is in the lower left hand corner ('before' (working backwards) the first record on the page).

Each of the items in the chart are described, below:

Pointers

Free Space Pointer

The free space pointer contains the location of the first byte of free space on the page (as shown in the diagram, where the last record on the page ends). On pages with no records yet stored, it points to the last byte on the page (either the very end, of just before the Reuse Queue Page Number described above).

Record Pointer Array

There are up to BRECPPG record pointers.

Table B Segments

Definition

As discussed below, bit maps are used

See also

Adding Records

The following Parameters relate to the Use of Table B

This table excludes the parameters used for Hash Key and Sorted Files. Please see those topics for a full discussion of their special parameters (and distinction in meanings for some of these).

BSIZE parameter	The number of pages in Table B.
BRECPPG parameter	The maximum number of record slots on a Table B page.