The transaction isolation global option
CICS® transaction isolation builds on CICS storage protection, enabling user transactions to be protected from one another. You can specify transaction isolation globally for a CICS region using the TRANISO system initialization parameter.
In addition to being able to specify the storage and execution key individually for each user transaction, you can specify that CICS is to isolate the user-key task-lifetime storage of a transaction to provide transaction-to-transaction protection. You do this by using the ISOLATE option of the TRANSACTION resource definition.
Transaction isolation does not apply to 64-bit storage.