The disposition (DISP) parameter describes the status of a data set to the system and tells the system what to do with the data set after the step or job terminates.

All new system-managed and VSAM data sets are treated as if DISP=(NEW,CATLG) were specified. They are cataloged at step initiation time.

To protect non-system-managed data sets in a shared environment, specify DISP=OLD for any data set that can be accessed improperly in a shared environment. Specifying DISP=OLD permits only one job step to access the data set. If the data set's share options permit the type of sharing your program anticipates, you can specify DISP=SHR in the DD statements of separate jobs to enable two or more job steps to share a data set. With separate DD statements, several subtasks can share a data set under the same rules as for cross-region sharing. When separate DD statements are used and one or more subtasks will perform output processing, the DD statements must specify DISP=SHR. For more details on sharing data sets see Sharing VSAM Data Sets.