Control Interval (CI) in z/OS Mainframe System

VSAM groups Individual Data records in to larger units of storage. These units of storage are called Control Intervals.

A Control Interval is the amount of data transfered between the auxiliary storage and virtual storage.

Control Interval has 4 components.

1) Data
2) Control Interval Descriptor Field (CIDF)
3) Record Descriptor Field (RDF)
4) Free Space.

CIDF - Contains the information about the free space within the CI.

RDF - Contains the information about the records within the data space.

Free Space - The Space between the Records and the Control Information is free space.