The exits must follow standard linkage conventions. They must save the registers on entry and restore the registers when they return. The exits must be reentrant, refreshable, and reusable.

If the processing done in the initialization exit requires clean-up to be performed, you must write a termination exit. For example, if the initialization exit obtains storage to return a new command buffer to the ALLOCATE command processor, you must provide a termination exit to free this storage.

The exits can use any of the TSO/E service routines. For a description of the service routines, see .

If the exits deal with device numbers, for example, on the ALLOCATE UNIT operand, the extended addressability capabilities, introduced with MVS/ESA SP 5.1, must be considered. Four-digit device numbers are preceded by a slash (/) to differentiate them from device types that contain only four-character numerics. Device numbers with less that four characters may be preceded by a preceding slash. See also the description on the ALLOCATE UNIT operand in if this needs to be considered.