Previous topic |
Next topic |
Contents |
Contact z/OS |
Library |
PDF
Segment Descriptor Word z/OS DFSMS Using Data Sets SC23-6855-00 |
|||||||||||
Each record segment consists of a segment descriptor word (SDW) followed by the data. The segment descriptor word, similar to the record descriptor word, is a 4 byte field that describes the segment. The first 2 bytes contain the length (LL) of the segment, including the 4 byte SDW. The length can be from 5 to 32␠756 bytes. The third byte of the SDW contains the segment control code that specifies the relative position of the segment in the logical record. The segment control code is in the rightmost 2 bits of the byte. The segment control codes are shown in Table 1.
The remaining bits of the third byte and all of the fourth byte are reserved for possible future system use and must be 0. The SDW for the first segment replaces the RDW for the record after
the record is segmented. You or the operating system can build the
SDW, depending on which access method is used.
|
Copyright IBM Corporation 1990, 2014
|