Selecting pageable, DREF, or fixed storage

Whether you choose pageable, DREF, or fixed storage depends on the extent to which your program is running disabled for external and I/O interrupts. To determine the type of storage you require, use the following guidelines:

If your program runs enabled for external and I/O interrupts, use pageable storage. If your program requires fixed storage for only a short interval, use the PGSER macro to page-fix the storage area as needed.
If your program meets the following criteria, consider using DREF storage:
- Runs disabled for external and I/O interrupts
- Has no requirement for constant real addresses backing virtual addresses
- Is authorized to obtain storage in storage key 0.
Attention: Before choosing DREF storage, read Obtaining and using disabled reference (DREF) storage, for information about special recovery requirements for its use.
If your program runs disabled for external and I/O interrupts for the duration of its processing and requires constant real addresses backing virtual addresses, use fixed storage. Note that the storage area must be non-swappable (either located in common storage or in a non-swappable address space) to have fixed real addresses.

You should select the type of storage that meets your needs while minimizing your use of central storage. Central storage is the most limited resource, followed by expanded storage, followed by auxiliary storage.

Pageable and DREF storage are backed by central storage only when the virtual storage is referenced. Fixed storage is always backed by central storage.