API64R start option


   .-API64R--=--YES-.   
>>-+----------------+------------------------------------------><
   '-API64R--=--NO--'

Note:

API64R is only meaningful if the machine is operating in z/Architecture® mode.
API64R=NO may cause a data move. Use API64R=YES unless API64R=NO is required.

Specifies whether 64-bit backed CSM data space storage can be passed to VTAM® and TCP/IP application programs.

Storage that is 64-bit backed is storage that, when fixed, can be assigned to real storage frames on or above the 2 Gigabyte real storage bar. With only a few exceptions, all CSM data space storage acquired by VTAM and TCP/IP when operating in z/Architecture mode is 64-bit backed.

When API64R=YES, application programs that accept CSM data space buffers for a receive operation will likely be given 64-bit backed CSM data space storage. If an application attempts to issue the LRA instruction (Load Real Address) against this storage, and the storage is resident on or above the 2 Gigabyte real storage bar, a special operation exception program interrupt will occur. Note that LRA is used primarily in preparation for I/O. There are no known application programs that perform I/O directly into or out of CSM data space storage.

In the unlikely event that an application program experiences this special operation exception, API64R=NO can be used to provide temporary relief. API64R=NO forces all data in 64-bit backed CSM data space to be copied to 31-bit backed CSM data space before being passed to an application program as part of a receive operation. The application program support team should be notified of the program interruption and once the application program has been modified to handle 64-bit backed storage, API64R=YES should be reinstated.

API64R=YES: Allows 64-bit backed storage to be passed to all VTAM and TCP/IP application programs.
API64R=NO: Forces all storage being passed to VTAM and TCP/IP application programs to be 31-bit backed.