The set of entries to be written to the cache structure is identified by write-operation-blocks that are contained in the storage area defined by BUFFER or BUFLIST. Each write-operation-block, mapped by the IXLYWOB macro and refered to here as a WOB, contains the information needed to identify an individual cache entry to be written.

The write-operation-blocks are numbered starting with 1. Each WOB has a length of 256 bytes. When BUFFER is specified, 1 to 256 WOBs can be provided by the user. When BUFLIST is specified, 1 to 16 WOBs can be provided by the user.

The data area containing the entries to be written to the cache structure is referenced through the DATAOFFSET keyword. DATAOFFSET specifies an offset in 256-byte increments into the BUFFER or BUFLIST storage areas that identifies the first data area.