IBM OS/390 User Manual

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┌───────────────────────────────────────┐
─────
│ SVA -
2,304K
├───────────────────────────────────────┤
5,184 K
│ F1 - VSE/POWER -
832K
├───────────────────────────────────────┤
│ F7 - DATABASE - 2,048K
├─────────┬─────────┬─────────┬─────────┤
─────
│ UNUSED │ UNUSED │ UNUSED │
│ UNUSED │ 128K
│ 64K
│ 3,036K │
│ 512K
├─────────┤
├─────────┤
├─────────┤
├─────────┤ CICS
│ F6 1.5M │F9 1,536K│
│FB 4,096K│
│ │ │
CICS
TOR
10,816 K
├─────────┼─────────┤
PROD
├─────────┤
│ F5 1.5M │
CICS
│ACF/VTAM │
├─────────┤
PRD1
│ │ │
│ F4 1.5M │
├─────────┤FA 5,504K│ F3 10.8M│F2 3,684K│
│ BG 1.5M │
├─────────┴─────────┴─────────┴─────────┤
─────
SUPERVISOR
-
384K
└───────────────────────────────────────┘
Figure 2. VAE with Four Address Spaces
Figure 2 is an example of how a customer would relieve the limitation of a 7MB
private address space as depicted in the previous diagram. The 7MB limitation
results from cross-system functions (for example, POWER and VTAM) having to
reside in the shared area. Shared area requirements reduce the amount of
virtual storage available for private area address spaces. In the above example
ACF/VTAM is moved to a private address space from the shared area. This
results in an additional 3.5MB for the private area address spaces. When VTAM
is moved it was also necessary to move any VTAM applications into the same
address space as VTAM. In this instance customers would run a CICS Terminal
Owning Region (
TOR) in the same address space with VTAM. The CICS TOR
would then communicate with one or multiple CICS Application Owning Regions
(
AORs) running in another address space. The CICS AOR was often the reason
for additional private area virtual storage.
Chapter 1. Why Customers Migrate
7