The CSA24 start option specifies the maximum amount of 24-bit addressable common service area (CSA) that can be used by VTAM®. The largest possible value for CSA24 is 16 megabytes.

The CSA24 start option limits only the amount of 24-bit addressable storage explicitly requested by VTAM. The CSA24 limitations do not apply when MVS™ returns 24-bit addressable storage in response to a VTAM storage request above the 16-megabyte line. MVS returns 24-bit addressable storage below the line because not enough CSA above the line is defined. CSA storage can be allocated from above or below the line depending on where the allocating procedure resides.