VM/370 Size = 3M IEA760A Response = ROO, '6144'
Nonpaging mode is not initiated. The explicit response sets virtual
storage sFace to 6 megabytes which lS1 requires for paging space. When VM/VS handshaking is active, VS1 closes the CP spool files when
the job output from the VS1 DSO, terminator, and output writer is
complete. Once the spool files are closed, V5/370 processes them and
sends them to the real printer or punch without operator intervention.
During its job output termination processing, VS1 issues DIAGNOSE cede X'OS' instructions to pass the CP CLOSE command to VM/370 for each
CP spool file. When a nonhandshaking copy of VS1 (prior to Release 4.0) is run under VM/370, the storage considerations are the same as if VS1 were running
in native mode. The iS1 virtual storage space must be at least 512K
larger than the virtual machine storage space.
The VS1 virtual storage space is specified at VS1 system generation tiae and can be altered in response to the IPL message IEA760A SPECIFY VIRTUAL STORAGE SIZE. The virtual machine storage space is specified
initially in the VM/370 directory and can be altered by using the CP
DEFINE STORAGE command. When an operating system in a virtual machine has enabled the ETAM autopoll feature, it notifies VM/370 (via a DIAGNCSE instruction)
whenever the autopoll CCWs are modified. VM/37C then modifies the real CCWs and does not check the autopoll CCWs for modifications each time
the string is executed. This CCW change detection reduces V8/370 overhead and thereby improves the overall performance. [Qte: If the autopoll feature is disabled for VM/370 (by the SET AUTOPOLL OFF command), a performance degradation occurs. When VS1 without handshaking is run in the Ve/370 environment some
duplicaticn of function results. Because VS1 must perform certain
functions when it is run on a real machine, it continues to perform all
those functions in a VM/370 virtual machine, even though V5/370 also
provides the services. However, with handshaking, VS1 avoids using many instructions and procedures that are redundant or less efficient in
the VM/370 environment.
114 IBM VM/370 operating in a Virtual Machine

In either Faging or nonpaging mode, VS1 avoids using: • ISK (insert storage key) and SSK (set storage key) instructions;
instead, VS1 uses a protection key table • Seek separation for 2314 direct access devices • The ENABLE/DISABLE sequence in the VS1 I/O supervisor (lOS) • TCH (test channel) instructions preceding SIO instructions • PCI (pregram-controlled interruptions) in the BTAM autopoll CCi sequence
In nonFaging mode, VS1 with handshaking avoids using: • LRA (lead real address) and RRB (reset reference bit) instructions
(this is especially important when virtual machine assist is not
enabled) • The DIAGNOSE code X'10' instruction to release virtual pages or
discontiguous storage • VS1 paging and CCi translation
IBM 3850 MASS STORAGE SYSTEM CONSIDERATIONS There are no special system generation requirements when generating OS/VS (OS/VS1 or OS/VS2 MVS) to use the MSS and operate in a virtual
machine. Any VS1 or MVS system that supports the MSS can use VM/370 MSS support. VM/370 MSS support allows a VS1 or MVS virtual machine to: • Use a dedicated mass storage control (MSC) port (or channel
interface) and dedicated 3330V devices
--and-- • Act as the host for the VM/370 communicator program communicates 3330V mount and demount orders and responses between the MSC and VM/370) Hewever, this sUFPort requires each 3330V address defined in OS/VS to be
identical te the 3330V address defined both to and to the virtual machine using it.
For details about how to generate V8/370 to support the MSS and to
install the VM/370 communicator program in either VS1 or MVS, refer to For details about how VM/370 communicates with the MSS and uses it as well as how to provide tackuF and recovery for MSS volumes, refer to For details about MSS initialization, refer to Generating OS/VS Under VM/370 This topic discusses the major steps for generating as/vs in a virtual machine under VM/370. While the following procedures are for generating VS1, they are similar enough to SVS and MVS procedures to be used as examFles. The primary difference between generating VS1 and SVS or MVS under VM/370 is VM/iS handshaking for VS1. Handshaking requires that a
user specify the VM option in the VS1 SCHEDULR macro instruction.
section 4. OS/VS in a Virtual Machine 115