Expanded storage only hiperspaces

An ESO hiperspace is available to supervisor state programs or problem state programs with PSW keys 0 through 7. To use the hiperspace, a program must have the STOKEN for the hiperspace. An ESO hiperspace is backed by expanded storage only. To back this storage, the system does not use auxiliary storage slots; data movement does not include paging I/O operations. However, in a peak-use situation:

The system might not be able to back the data you are writing to the hiperspace.
The system might take away the expanded storage that backs the hiperspace.

These actions cause the data in an ESO hiperspace to be volatile. Therefore, use an ESO hiperspace only if you are prepared to handle unsuccessful read operations. You can use this hiperspace to get quick access to the data there. But, in a peak-use condition, when the system takes the expanded storage away from the hiperspace, the program must be prepared to read data from a permanent backup copy on DASD or recreate the data that was in the hiperspace.

When the system swaps the address space out, it discards the data in any hiperspace that is owned by TCBs that are running in the address space. For this reason, you might consider making such an address space non-swappable.