8.193 XPNDSIZE (Display or set expanded storage size)

8.193.1 Function

The XPNDSIZE command is used to specify the size of the main storage in megabytes. Given without an
argument the XPNDSIZE command displays the current size of the expanded storage. Storage is alloca-
ted in megabytes, unless a specific unit is specified. The actual upper limit of the expanded storage is
determined by the host system's architecture, operating system, and on some systems the amount of
physical memory and paging space you have available. The lower limit is 0.

The practical limit depends on the maximum amount of storage that can be obtained by “malloc” (usually
around 1 GB on 32-bit platforms; on 64-bit platforms the value should only be limited by available paging
space).

When increasing the expanded size Hercules attempts to allocate first the new storage. If the new allo-
cation is successful then the previously allocated memory will be freed. This is to prevent a situation
where the old memory is freed first, then the new allocation fails and a reallocation of the memory in the
previous size also fails because of storage fragmentation and therefore leaving Hercules without memory.

When decreasing the expanded storage the memory will stay allocated in the previous size but the
storage size will appear as decreased. Subsequent increases will not reallocate memory unless they go
over the already allocated amount.

An additional optional argument determines the locking state of the allocated memory (page lock by host
operating system). The LOCKED option indicates that the memory is to be locked into storage while UN-
LOCKED (the default) indicates that the memory is not locked into the storage.

Please note that Hercules preserves the last locking state of XPNDSIZE. Once storage is locked, any
subsequent change to the expanded storage size will honor the existing lock state of memory unless the
lock state is specified again on the XPNDSIZE command.

Caution: Do not lock expanded storage unless sufficient real memory is available to back up the request.
Failure to do so may require the host system to be rebooted.

8.193.2 Syntax

Descriptive

xsize[ ]

Diagram

Êʬ¬¬ ¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬§¬¬¬¬¬¬¬¬¬¬¬ÊÍ

~¬¬¬ ¬¬¬® OCK ¬¬¬®

¬¬¬ xsize ¬¬¬¦¬¬¬¬¬¬¬¬¬¦¬¬¬¦¬¬¬¬¬¬¬¬¬¬¬¬¬¬¦¬¬¬

¬¬¬ ¬¬¬« LOCK

¬¬¬ T ¬¬¬

8.193.3 Parameter

size

The value of xsize must be a valid decimal number. The actual upper limit is deter-
mined by the host system’s architecture, the operating system and on some sys-
tems the amount of physical memory and paging space that is available.

Storage sizes not on a 1M boundary are rounded up to the next 1M boundary. The
lower limit and default is 0.

M

‘M’ determines that the number given is specified in megabytes (multiplier 2**20).
This is the default if no unit is appended.

G

‘G’ determines that the number given is specified in gigabytes (multiplier 2**30).

T

‘ T’ determines that the number given is specified in terabytes (multiplier 2**40). On
32-bit machines the unit terabytes is not available.

LOCK

Attempt to lock the storage (pages locked by the host operating system).

UNLOCK

Leave the store unlocked (no pages locked by the host operating system). This is
the default.

Notes:

The actual upper limit is determined by the host system’s architecture and operating system, the guest
operating system and the amount of physical memory and available paging space.

The total of MAINSIZE and XPNDSIZE on host systems with a 32-bit architecture will be limited to less
than 4G; host systems with a 64-bit architecture will be limited to less than 16E.

Use of storage sizes greater than supported by the guest operating system may generate incorrect
results or error conditions within the guest operating system.

8.193.4 Overview Storage Allocation Units

Unit

Multiplier

Name (Symbol)

IEC Name (IEC Symbol)

Restrictions

M

2**20

Megabyte (MB)

Mebibyte (MiB)

G

2**30

Gigabyte (GB)

Gibibyte (GiB)

T

2**40

Terabyte (TB)

Tebibyte (TiB)

Not on 32-bit machines

Table 24: Storage Allocation Units