Figures C–1 through C–4 illustrate the word layouts for the absolute address (AA) word, the in-use table control word (TCW), the available TCW, and the table serial number (TSN).

Absolute Address (AA) Word Layout

The following figure illustrates the word layout for the absolute address (AA) word.

            A A A A A A   A * B B B B
            A A A A A A   A * B B B B
            A A A A A A   A * B B B B
            A A A A A A   A * B B B B

            A    47: 28     BAF (block address field)

                     Block address.

            *    19: 04

                     Zeros when on disk.
                     Certain bits can be turned on
                     when in certain in-core tables
                     of the DBS.

            B    15: 16     WAF (word address field)

                     Word offset to first word of
                     record from the first word of the
                     block (=0).

Data set records are located using absolute address (AA) words. All AA words have a consistent format; they contain a block address and a word address. The block address is the segment number of the first segment of the block. The word address gives the word offset within the block at which the record begins. Both address spaces begin at 0 (zero) offset.

When a data set is sectioned, all AA words pointing to that data set are expanded by one word to include information indicating the section number to which the basic AA word applies.

In-Use Table Control Word (TCW) Layout

The following figure illustrates the layout for the in-use TCW.

            A A A A B B   B B B B B B
            A A A A B B   B B B B B B
            A A A A B B   B B B B B B
            A A A A B B   B B B B B C

            A    47: 16     TABLESTART

                     Word index from start of block (=0)
                     of the first in-use table entry.

            B    31: 31     TABLECOUNT

                     Number of in-use entries in the table.
                     The first in-use entry is numbered one.

            C    00: 01     FINE TABLE BIT

                     0 = Coarse, coarse-coarse, and so on.
                     1 = Fine table.

                     Valid for index sequential only.
                     For other structures, this bit
                     can be 0 or 1 and is ignored.

Available Table Control Word (TCW) Layout

The following figure illustrates the layout of the available TCW.

            A A A A A A   A A A A A A
            A A A A A A   A A A A A A
            A A A A A A   A A A A A A
            A A A A A A   A A A A A A

            A    47: 48

                     Block address of next available table.

Table Serial Number (TSN) Layout

The following figure illustrates the layout of the TSN.

            A A A A A B   B B B B B B
            A A A A A B   B B B B B B
            A A A A B B   B B B B B B
            A A A A B B   B B B B B B

            A    47: 18     TOPTSNF

                     Top part > 0 when recovery has backed
                     out some changes to the current table
                     and the table has not yet been changed
                     again.

            B    29: 30     BOTTOMTSNF

                     Bottom part is the principal part.

The two fields of the TSN synchronize the table with the audit. Their use results in less information being audited than would otherwise be the case.