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Step 3 - I/O operations

Depending upon the underlying operating system, z/OS or z/VM, there are three possible types of I/O (Input / Output) operation.

DISKR - read, is supported by both z/OS and z/VM.

DISKW - write, is supported by both z/OS and z/VM.

DISKRU - read for update is supported by z/OS.

I/O Operations

DISKR - Read

This retrieves records from a file or data set into memory

Records can be retrieved individually or in groups, and processing does not have to start at the beginning of the file or data set.

DISKW - Write

This transfers records from memory to a file or data set.

Records can be written individually or in groups.

DISKRU - Read for Update

This retrieves a single record which can be altered.

The subsequent updated will be achieved by a DISKW operation, which overwrites the existing record.