tableBASE uses data spaces for the local TSR and VTS-TSR. This allows the size of a TSR to be up to 2 GB. The use of data spaces also means that TSRs are protected against accidental overwrites by faulty application programs, and that no space is taken up for the local TSR from the region’s above-the-line virtual memory. (Maximum table size is limited by the maximum 2 G size minus the system overhead.)
Data spaces used for the VTS-TSRs do not affect the MAXCAD parameter of the MVS operating system. An IEFUSI MVS system exit may limit data space usage.
tableBASE loads the table into the data space and allows the operating system to handle paging, rather than having tableBASE paging individual blocks to and from a much slower DASD-based tableBASE library.