IBM z13s Technical Manual page 154

Certain z/Architecture operating systems, such as z/OS,
mode and operate in 64-bit mode. Other z/Architecture operating systems, such as z/VM, can
be configured to change to 64-bit mode or to stay in 31-bit mode and operate in the ESA/390
architecture mode.
The following modes are provided:
z/Architecture mode: In z/Architecture mode, storage addressing is 64-bit, allowing for
virtual addresses up to 16 exabytes (16 EB). The 64-bit architecture theoretically allows a
maximum of 16 EB to be used as main storage. However, the current main storage limit for
LPARs is 10 TB of main storage on a z13s server. The operating system that runs in
z/Architecture mode must be able to support the real storage. Currently, z/OS supports up
to 4 TB
Expanded storage also can be configured to an image that runs an operating system in
z/Architecture mode. However, only z/VM can use expanded storage. Any other operating
system that runs in z/Architecture mode (such as a z/OS or a Linux on z Systems image)
does not
configured to this image and is not used.
ESA/390 architecture mode: In ESA/390 architecture mode, storage addressing is 31 bit,
allowing for virtual addresses up to 2 GB. A maximum of 2 GB can be used for main
storage. Because the processor storage can be configured as central and expanded
storage, memory above 2 GB can be configured as expanded storage. In addition, this
mode allows the use of either 24-bit or 31-bit addressing, under program control.
Because an ESA/390 mode image can be defined with up to 128 GB of main storage, the
main storage above 2 GB is
Storage resources: Either a z/Architecture mode or an ESA/390 architecture mode
operating system can run in an ESA/390 image on a z13s server. Any ESA/390 image
can be defined with more than 2 GB of main storage, and can have expanded storage.
These options allow you to configure more storage resources than the operating
system can address.
ESA/390 TPF mode
In ESA/390 TPF mode, storage addressing follows the ESA/390 architecture mode. The
z/TPF operating system runs in 64-bit addressing mode.
Coupling facility mode
In coupling facility mode, storage addressing is 64 bit for a coupling facility image that runs at
CFCC Level 12 or later. This configuration allows for an addressing range up to 16 EB.
However, the current z13s definition limit for LPARs is 1 TB of storage.
CFCC Level 21, which is available for z13s servers with driver level 27, introduces several
enhancements in the performance, reporting, and serviceability areas.
CFCC Level 19, which is available for the zEC12 with driver level 15F, introduces several
improvements in the performance and resiliency areas, including Coupling Thin Interrupts
and Flash Express.
For more information, see 3.9.1, "Coupling Facility Control Code" on page 132. Expanded
storage cannot be defined for a coupling facility image. Only IBM CFCC can run in the
coupling facility mode.
5
1 TB if an I/O drawer is installed in the system (carry forward only).
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IBM z13s Technical Guide
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of real storage (z/OS V1R10 and later releases).
address the configured expanded storage. This expanded storage remains
not
always
used. Instead, it remains configured to this image.
change the 31-bit addressing