A control interval(CI) is the unit of information that VSAM transfers between virtual and auxiliary storage.
A group of control intervals makes up a control area(CA).
Control Interval is analogous to a physical block for QSAM files. It is the unit of I/O.Must be between 512 bytes to 32k. Usually either 2K or 4K. A larger control interval increases performance for sequential processing while the reverse is true for random access. Under CICS when a record is locked, the entire CI gets locked.
Control Area is a group of control intervals. CA is used during allocation. CA size is calculated based on the allocation type (cyl, tracks or records) and can be max of 1 cylinder.
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