When both VM/310 and VS1 support handshaking, full handshaking results
when VS1 runs in nonpaging mode. However, handshaking does not require
nonpaging mode. When VS1 is run under the control of it
executes in nonpaging mode if: • Its virtual storage space is equal to the storage space of the VM/310 virtual machine. • Its virtual machine storage space is at least 1 megabyte. • VM/VS handshaking is available.
The VS1 virtual machine operator initiates nonpaging mode by issuing the CP SET PAGEX ON command. Provided that the above conditions are satisfied when VS1 is loaded
under control of VM/370, VS1 issues a special message after the IEA160A SPECIFY VIRTUAL STORAGE SIZE message:
IEA788I NON-PAGING MODE OF OS/VS1 UNDER VM/370 When VS1 executes in nonpaging mode, it uses fewer privileged
instructions and avoids duplicate paging. The VS1 nucleus
initialization program (NIP) fixes all VS1 pages to avoid duplicate
paging. !2ig: The VM/310 working set size (the estimated number of real storage pages that a virtual machine needs to execute) may be larger for a VS1 virtual machine in nonpaging mode than for one not in nonpaging mode.
Considerations unique to nonpaging mode are:
An EOS or U response to the VS1 SPECIFY VIRTUAL STORAGE SIZE message
automatically sets the VM/370 virtual storage space equal to the VS1 virtual machine storage space, provided the latter is 1 megabyte or
larger. • Storage limits for ncnpaging mode are the same as for VS1 itself: VS1 Release 6 has a 16 megabyte storage limit in nonpaging mode
and an 8 megabyte limit in paging mode (the limit is equal to the
real machine size or configuration as supported by VS1). During IPL, VS1 issues a message that specifies these limits. VS1 Release 5 has a 4 megabyte storage limit and issues a
message to that effect. VS1 Release 4 has a 4 megabyte storage limit, but issues no
message to that effect.
A minimum size VS1 nonpaging mode. It
partitions.
nucleus tends to be
provides more space
more suitable
for problem
112 IBM '5/370 Operating Systems in a Virtual Machine for the program

In nonpaging mode, VS1 maps virtual storage normally; that is, it
puts these functions in the high addresses of virtual storage: the JES buffer pool, VTAM workspace, RTAM area, JES routines, resident
modules, and the pageable supervisor. By minimizing the virtual
storage requirements for these functions, VS1 can provide more
problem program partition space.
The VS1 paging data set is not used in nonpaging mode. The VS1 system does not require page parameters and page packs. • It is possible to execute V=R jobs in nonpaging mode. The V=R line
is a valid IPL parameter and the V=R logic within VS1 is applicable.
However, any benefits from such operation would appear to be
questionable because the entire VS1 system functions V=R in nonpaging
mode. FASTNIP automatically forces nonpaging mode when the virtual machine
storage space is 1 megabyte or largerc !2te: Although handshaking does not require nonpaging mode, may be
occasions te run a VS1 system in a virtual machine with a storage space
of 1 megabyte or larger and not use nonpaging mode. To avoid initiating
nonpaging mede, specify the virtual storage space explicitly to VS1 in
response to message IEA760A; for example: ROO, '6144'.
The following examples show whether nonpaging mode is initiated when
initializing VS1 in a V8/370 environment with handshaking. V8/370 Size = 768K OS/VS1 Virtual Storage Size = 6M IEA760A Response = 'EOB'
Nonpaging mede is not initiated, and the virtual machine storage space
is less than 1M. l: VM/370 Size = 18 OS/VS1 Virtual Storage Size = 6M IEA760A Response = 'U' Nonpaging mode is initiated, and VS1 forces the virtual machine storage
space to 1 megabyte. The VS1 system may not complete initialization
because of insufficient virtual storage space. i8/370 Size = 4M OS/iS1 Virtual Storage Size = 4M IEA760A Response = ROO, '4096' Nonpaging mode is initiated, and the explicit response happens to equal
virtual machine storage space. Section 4. as/vs in a Virtual "achine 113