VSAM Share Options are what decide who may see certain VSAM datasets. Using these controls, you may provide varying degrees of access to a single VSAM dataset for various users/jobs. SHAREOPTS is the name of the parameter used in the DEFINE statement (a,b). Two or more users/jobs on the same MVS system may share a file using the cross-region share option denoted by letter a, whereas two or more users/jobs on separate MVS systems can use the cross-system share option denoted by letter b. Typically, this is the SHAREOPTS value (2 3). If the value for cross-region is 2, then numerous users may work on the file at once, but only one can be an updater. If the cross-system parameter is set to 3, then any number of jobs or users may utilise this file for processing (VSAM does not ensure integrity).