When VM/370 is not the primary operating system and the other operating
system is usually run without VM/310, generate the other operating
system to: • Be transparent to the users of the other system • Have the required number of partitions or regions Sha:ing the system residence volume avoids the need to keep multiple ccp1es of the operating system online. The shared system residence
volume should be read-only. To share OS/VS among users, remove all data
sets with write access from the system residence volume. OS/VS1 RECOMMENDATIONS When generating VS1 to run in a virtual machine, note the following
recommendations: The hardware storage size used by VM/310 may be larger or smaller than
the hardware storage sizes supported by VS1. In the VM/370 directory
for the VS1 user, use the USER statement to define the minimum and aaximum virtual storage sizes for the VSl virtual machine. For the VSl system, generate it to support the hardware storage size of the real
machine on which the VSl system is to run.
For example: In the USER directory statement, specify the minimum
and maximum storage sizes supported for the VS1 virtual machine. Define
the minimum storage size as 1 megabyte -- the minimum storage size
supported by VS1. Define the maximum storage size according to the VSl release level (such as VS1 Release 6, which has a 16 megabyte storage limit in nonpaging mode and an 8 megabyte storage limit in paging mode).
For the VS1 system to run more efficiently in the VS1 virtual machine,
generate its real storage size for 2 megabytes --the storage size of
the real processor. Thus, this system generation specification
establishes an initial VM/310 virtual storage size of 2 megabytes even
though the minimum VM/310 storage definition was 1 megabyte.
By using VS1 in nonpaging mode, VM/370 handles the paging and CCW translation for VS1, thereby eliminating the VS1 overhead associated
with these functions. For a description of VM/VS handshaking between VS1 and VM/370, refer to the topic "VM/VS Handshaking for VS1" later in
this section. Section 4. OS/VS in a Virtual Machine 109

When running VS1 in a V=R machine, a user can avoid data transfer
operations into real page zero by doing one of the following: • If the VS1 nucleus already exists, replace the existing ORDFR statement with the following linkage editor control statement in the VS1 linkage editor deck: ORDER IEAAIHOO,IEAIOSOO(P) Use all INSERT control statements that were produced during the
original VS 1 system genera tion process. • Generate a new VS1 nucleus prior to stage II execution and perform lOS alignment by modifying the ORDER control statement in the VS1 stage II job stream. VM/VS HANDSHAKING FOR VS1 VM/VS handshaking is a communication path between the control program
(CP) component of VM/310 and VS1 Release 4 (and subsequent releases)
running as a virtual machine under VM/310. To improve their operation with V8/310, systems generated to use VM/VS handshaking can run both in a real machine and in a virtual
machine. In a virtual machine, systems that have VH/VS handshaking can
more realistically simulate the operation of their real machine. • VH/VS handshaking consists of:
Closing CP spool files when job output
allows VM/310 to immediately process
operator intervention.
is complete.
these output
This fu nction
files without • Processing pseudo page faults. When the pseudo page fault handling
portion cf handshaking is active, one task can be dispatched while
ancther is waiting for a page to be brought into real storage. • Providing a nonpaging mode to eliminate duplicate paging. • Providing a way to avoid a PCI (programmed-controlled interruption)
in a BTAM autopoll CCW loop. • Providing miscellaneous enhancements when running under V8/310. Althcugh handshaking is a system generation feature for VS1, it is
active only when VS1 is run under the control of V8/310; it is disabled
when that same VS1 operating system is run on a real machine. The V8/VS bandshaking feature is active when: • VS1 is generated with the VM/310 option. • The virtual machine storage space is at least 1 megabyte.
Note: If mode is used, refer to the subtopic "VS1 Nonpaging Mcde" described later in this discussion. 110 IBM 370 operating systems in a Virtual Machine