XABALL

   The allocation control XAB (XABALL) provides additional control
   over file or area space allocation on disk devices in order to
   optimize performance.

   When RMS uses a XAB to create or extend an area, the following
   XABALL fields duplicate and take precedence over associated
   fields in the related FAB:

   o  The allocation quantity (ALQ) field, XAB$L_ALQ, overrides
      FAB$L_ALQ

   o  The bucket size (BKZ) field, XAB$B_BKZ, overrides FAB$B_BKS

   o  The default extension quantity (DEQ) field, XAB$W_DEQ,
      overrides FAB$W_DEQ

   o  The XAB$V_CBT and XAB$V_CTG options of the allocation options
      field, XAB$B_AOP, override the FAB$V_CBT and FAB$V_CTG options
      of the file-processing options field, FAB$L_FOP

   The following table lists the symbolic offset, the size in bytes,
   the FDL equivalent, and a brief description of each field.

   Offset      Size   FDL Equivalent      Description

   XAB$B_AID   1      AREA n              Area identification number
   XAB$B_ALN   1      AREA POSITION       Alignment boundary type
   XAB$L_ALQ   4      AREA ALLOCATION     Allocation quantity
   XAB$B_AOP   1      AREA                Allocation options
   XAB$B_BKZ   1      AREA BUCKET_SIZE    Bucket size
   XAB$B_BLN   1      None                Block length
   XAB$B_COD   1      None                Type code
   XAB$W_DEQ   2      AREA EXTENSION      Default extension quantity
   XAB$L_LOC   4      AREA POSITION       Location
   XAB$L_NXT   4      None                Next XAB address
   XAB$W_RFI   6      AREA POSITION       Related file identifier
                      FILE_ID
                      or FILE_NAME
   XAB$W_VOL   2      AREA VOLUME         Related volume number