The virtual storage address space

A two-gigabyte virtual storage address space is provided for:

The master scheduler address space
JES
Other system component address spaces, such as allocation, system trace, system management facilities (SMF), and dumping services
Each user (batch or TSO/E).

The system uses a portion of each virtual address space. Each virtual address space consists of:

The common area below 16 megabytes
The private area below 16 megabytes
The extended common area above 16 megabytes
The extended private area above 16 megabytes.

Figure 1 shows the layout of the storage areas for an address space in virtual storage. Note that most of the system areas exist both below and above 16 megabytes, providing an environment that can support 24-bit, 31-bit, and 64-bit addressing. However, each area and its counterpart above 16 megabytes can be thought of as a single logical area in virtual storage.

Figure 1. Virtual storage layout for a single address space

The common area contains system control programs and control blocks. The following storage areas are located in the common area:

Prefixed storage area (PSA)
Common service area (CSA)
Pageable link pack area (PLPA)
Fixed link pack area (FLPA)
Modified link pack area (MLPA)
System queue area (SQA)
Nucleus, which is fixed and nonswappable.

Each storage area in the common area (below 16 megabytes) has a counterpart in the extended common area (above 16 megabytes) with the exception of the PSA.

For more information about using storage above the 2-gigabyte address, see z/OS MVS Programming: Extended Addressability Guide.

Each address space uses the same common area. Portions of the common area are paged in and out as the demands of the system change and as new user jobs (batch or time-shared) start and old ones terminate.

The private area contains:

A local system queue area (LSQA).
A scheduler work area (SWA).
Subpools 229, 230, and 249 (the authorized user key area).
A 16K system region area.
Either a V=V (virtual = virtual) or V=R (virtual = real) private user region for running programs and storing data.

Except for the 16K system region area and V=R user regions, each storage area in the private area below 16 megabytes has a counterpart in the extended private area above 16 megabytes.

Each address space has its own unique private area allocation. The private area (except LSQA) is pageable unless a user specifies a V=R region. If assigned as V=R, the actual V=R region area (excluding SWA, the 16K system region area, and subpools 229, 230, and 249) is fixed and nonswappable.