Table C (File architecture)

Table C is a hashed table divided into entries of seven bytes each. Table C entries store index information for fields that have the KEY or the NUMERIC RANGE attributes.

Overview

Model 204 creates a chain of entries in Table C for each value stored in a KEY field and several chains of entries for each value stored in a NUMERIC RANGE field.

Identifying Record(s) From the Chain

In the segment entries, there are two possible references to record(s):

• If, in that segment, there is one and only one record, with that combination of field and value, there is a direct pointer to the record (the IRN is physically stored in the Table C entry).
• Otherwise, the segment will point to a list or bitmap page.

It is quite possible that, for a particular field value pair, some of the segment pointers will point to records, and others will point to list / bitmap pages.