Chapter 3. Central processor complex system design 125
Before you activate an LPAR, main storage (and optionally, expanded storage) must be
defined to the LPAR. All installed storage can be configured as main storage. Each z/OS
individual LPAR can be defined with a maximum of 4 TB of main storage. z/VM supports 1 TB
of main storage.
Main storage can be dynamically assigned to expanded storage and back to main storage as
needed without a POR. For more information, see “LPAR single storage pool” on page 116.
Memory
cannot be shared between system images. It is possible to reallocate dynamically
storage resources for z/Architecture LPARs that run operating systems that support dynamic
storage reconfiguration (DSR). This process is supported by z/OS, and z/VM V5R4 and later
releases. z/VM, in turn, virtualizes this support to its guests. For more information, see 3.7.5,
“LPAR dynamic storage reconfiguration” on page 129.
Operating systems that run as guests of z/VM can use the z/VM capability of implementing
virtual memory to guest virtual machines. The z/VM dedicated real storage can be shared
between guest operating systems.
Table 3-6 shows the z13 storage allocation and usage possibilities, depending on the image
mode.
Table 3-6 Main storage definition and usage possibilities
ESA/390 mode
In ESA/390 mode, storage addressing can be 31 or 64 bits, depending on the operating
system architecture and the operating system configuration.
An ESA/390 mode image is always initiated in 31-bit addressing mode. During its
initialization, a z/Architecture operating system can change it to 64-bit addressing mode and
operate in the z/Architecture mode.
Image mode Architecture mode
(addressability)
Maximum main storage Expanded storage
Architecture z13s
definition
z13
s
definable
Operating
system usage
a
a. z/VM supports the use of expanded storage, but expanded storage is not recommended for z/VM V6.3.
ESA/390 z/Architecture (64-bit) 16 EB 4 TB Yes Yes
ESA/390 (31-bit) 2 GB 128 GB Yes Yes
ESA/390 TPF ESA/390 (31-bit) 2 GB 2 GB Yes No
Coupling facility CFCC (64-bit) 1.5 TB 1 TB No No
Linux only z/Architecture (64-bit) 16 EB 1 TB Yes Only by z/VM
ESA/390 (31-bit) 2 GB 2 GB Yes Only by z/VM
z/VM
b
b. z/VM mode is supported by z/VM V6R2 and later.
z/Architecture (64-bit) 16 EB 1 TB Yes Yes
zACI z/Architecture (64-bit) 16 EB 1 TB Yes No
Note: When an I/O drawer (carry forward only) is installed, the maximum amount of LPAR
memory is limited to 1 TB.
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