HSTYPE=CACHE tells the system that your program (in supervisor state or PSW key 0 - 7) wants an ESO hiperspace, the kind of hiperspace that offers your program a high-speed cache area.

The CASTOUT parameter on DSPSERV is available only for ESO hiperspaces. This parameter gives the system some indication of the priority of the data in the hiperspace. CASTOUT tells the system how hard it should try to keep the data in the hiperspace. The system looks at this parameter when it makes the decision to take the expanded storage backing from the hiperspace. If you use CASTOUT=NO, the system persists in trying to keep the hiperspace data. It tells the system to give the hiperspace higher priority when it searches for pages to remove from expanded storage when a shortage arises.

Note that specifying CASTOUT=NO can place a heavy demand on expanded storage and does not always protect the data. Use it only when you are willing to sacrifice overall system performance to have better availability of the data. Certain factors might cause the pages to be discarded regardless of CASTOUT=NO. For example, if the system swaps out the address space that owns the hiperspace, it discards pages without regard to CASTOUT. To prevent loss of data due to a swapped-out address space, make the address space that owns the hiperspace non-swappable.

Example of Creating an ESO Hiperspace™

* CREATE AN ESO HIPERSPACE
         .
DSPSERV1 DSPSERV CREATE,NAME=NAME,STOKEN=STOKEN,ORIGIN=ORIGIN       X
             BLOCKS=BLOCKS,TYPE=HIPERSPACE,HSTYPE=CACHE,CASTOUT=NO
         .
* CONSTANTS AND VARIABLES
         .
NAME       DC  CL8'HSDS01  ' NAME OF THE HIPERSPACE
BLOCKS     DC  F'100'        SIZE OF THE HIPERSPACE IN BLOCKS
ORIGIN     DS  AL4           START ADDRESS OF THE HIPERSPACE
STOKEN     DS  CL8           STOKEN RETURNED FROM DSPSERV CREATE