r , The fcllowing recommendations have been made by users who runl I DOS/VS in a virtual machine under VM/370. As such, thesel Irecommendations have not been submitted to any formal IBM tests.1 IPrier to any implementation, an installation should evaluate their I lusefulness in its own configuration. I VM/370 RECOMMENDATIONS When generating VM/370 for a DOS/VS virtual machine, note the following
recommendations: IPL time can be reduced by saving any operating system after the
generated operating system has been loaded on VM/370. For more
information about generating saved systems, refer to the DOS/VS Release 34 with the Advanced Functions-DOS/VS program Product (Program No. 5746-IE2) uses VM/VS handshaking. The use and efficiency
of DOS/VS with handshaking is similar to using VS1 handshaking with VM/370. For further details, refer to the appropriate DOS/VS program
product publications. DOS/VSE with the VSE/Advanced Functions program Product (5746-XES) uses VM/VS handshaking (also known as the DOS/VSE-VM/370 linkage
facility). The use and efficiency of DOS/VSE with handshaking is similar to using VS1 with handshaking. For further details, refer to GC33-6106.
Tc initialize a DOS/VS minidisk for use under VM/370, the IBCDASDI service program be used. If the whole disk is DOS/VS, any DOS or OS disk initialization program may be used. 70 IBM iM/370 Operating systems in a Virtual Machine VM/370 used by

DOS/VS RECOMMENDATIONS when generating DOS/iS to run in a virtual machine, note the following recommendations: • (DOS/VS Release 34 and earlier only) When generating a DOS/VS supervisor; use 4K (the size of VM/370's pages) whenever DOS/VS recommends using a 2K boundary or a multiple
of 2K. Thus, do not use the default for the SEND macro instruction.
It causes DOS/VS to round the supervisor size to the next 2K
boundary. Instead, manually calculate the size of the supervisor and
specify a 4K boundary in the SEND macro instruction. This
specification forces DOS/VS to be loaded at the next 4K page
boundary. • addresses Specify an address of-01P-in the VM/370 directory CONSOLE statement.
This specification allows the DOS/VS supervisor to run on the real
processor using the real console address of 01F. If CMS is also to be used, it uses console address 01F. In this
case, specifying 01F in the CONSOLE statement allows use of this
console with both DOS/VS and CMS virtual machines.
To use more than one DOS/VS console under V8/370 or to use a 3270 display device in display operator control mode, refer to the topic "Specifying More Than One Console in a Virtual Machine" in the "General Considerations" section of this publication. • Improve performance by reducing the number of privileged instructions
that must he handled by VM/370 and virtual machine assist. Generate
a tailored DOSjVS supervisor for each virtual machine and leave out
any unnecessary options. Because VM/370 issues its own stand-alone
seek (except for 2314 disks), do not specify seek separation in the FOPT macro instruction. When using DOS/VS Release 34 (or earlier) and the computer has
block multiplexer channels, specify the block multiplexer option in
beth the PIoes macro instruction and the directory OPTICN statement. However, this specification is unnecessary when using DOS/VSE hecause block multiplexer support is standard in DOS/VSE. Generate several tailored DOS/VS supervisors, if desired, and
store them on the same DOS/VS SYSRES with different supervisor names
(such as $$A$SUPn, where n is 1, 2, 3, 4, etc.).
Perfcrmance is usually better when using several victual machines rather
than using many active partitions in one virtual machine. That is, if
there is a ccmmunications system, a batch system, and a test system, create a separate virtual machine for each one. However, to only run VM/370 part of the day and to m1n1m1ze operational differences, one
multipartition production DOS/VS machine may be preferable. Section 3. DOS/VS in a Virtual Machine 71