With keyed access and addressed access, VSAM maintains the control information in a control interval. With control interval access, you are responsible for that information.

Note: A linear data set has no control information imbedded in the control interval. All of the bytes in the control interval are data bytes; there are no CIDFs or RDFs.

Figure 1 shows the relative positions of data, unused space, and control information in a control interval.

Figure 1. General Format of a Control Interval

For more information about the structure of a control interval, see Control Intervals.

Control information consists of a CIDF (control interval definition field) and, for a control interval containing at least one record, record slot, or record segment, one or more RDFs (record definition fields). The CIDF and RDFs are ordered from right to left. The format of the CIDF is the same even if the control interval size contains multiple smaller physical records.