Data set header prefix

The data set header begins with the standard four-byte control record prefix containing the combined length of all sections. Table 1 describes the format of the prefix section of the data set header.

Table 1. Fields in the Prefix Section of a Data Set Header
Field Name Offset in Hex Length Type of Data Default Value Valid Range Description
NDHLEN 0 2 binary none 4-32764 The Combined length of all sections in the data set header.
NDHFLAGS 2 1 binary none none Reserved for IBM's use.
NDHSEQ 3 1 binary none none The sequence indicator. It contains valid information after the header is segmented for transmission. The information specifies:
  • The position of the segment within the record.
  • More record segments to follow.
  .1 80 bit 0     High order bit means that more segments follow.
  .7 7F bit 0     Low order bits contain the segment number starting with zero (0).