It is usually best to make the DOS/VS partition sizes, and therefore
the whole DOS/VS virtual machine, large enough so that all jobs run V=B. Let VM/370 do the paging.
Rotational position sensing (RPS) cannot be used with V=B partitions.
Also, avoid double CCi translation and double paging. Set RSIZE equal to the supervisor size plus the sum of all V=R partitions, plus the SVA, plus 32K.
Note: An installa tion must specify ",REAL" on the DOS/VS / / EXEC job control card. When VM/370 is the primary operating system and DOS/VS is running one or
two partitions in a virtual machine, generate DOS/VS with as few options
as pessible, farticularly when several virtual machines share the same
system residence volume. When VM/370 is not the primary operating system and DOS/VS is usually
run without VM/370, generate DOS/VS to: • Be transparent to the users of the other systems • Have the required number of partitions When DOS/VS is run under VM/370, POWER (POWER/VS for DOS/VS or VSR/FCWEE fer DOS/VSE) should be used with the appropriate unit record devices
that are dedicated to DOS/VS. If an installation has sufficient DASD space, let both FOWER and VM/370 spool. Generate POWER with only the options that suit the
installation's needs, but make the I/O buffer sizes as large as
possible, up to 2008 bytes. If one job step in a DCS/VS job stream
abends, it is easy to use POWER to cancel the remainder of the job
stream. To use only VM/370 spooling, an installation must manually
cancel each jcb step.
There are two methods of sharing a DOS/VS system residence voluae: • Have a read/write DOS/VS system residence (SYSRES) minidisk for each DOS/VS virtual machine. Then share a read-only copy of the private
core image, relocatable, and source statement libraries. • Share a read-only copy of the DOS/VS SYSBES minidisk, and have
separate read/write private libraries for each virtual machine.
Because cnly one standard label cylinder is available, all virtual machines must coordinate their use of that cylinder. Which methcd is
situation.
used depends upon each installation's specific
72 VM/370 Operating Systems in a Virtual Machine

Page of GC20-1821-3 As Updated April 1, 1981 by TNL GN25-0840 When generating DOS/VS under VM/370, an installation must restore the DOS/VS PID tape onto a full disk pack; a minidisk cannot be used.
Create an operational system residence pack on a full pack, and then
use CORGZ to copy the DOS/VS SYSRES to a minidisk. Kake sure that ECMODE is set 'ON'. In the FOPT macro instruction, specify enough second level directory (SLD) entries to reduce repetitious reading of the directory. Use the system directory list (SDL) in the shared virtual area (SVA) for all job control, disk and tape open and close transients, and for
the attention routine.
If minidisks are used, although permitted on DOS/VS not use the same DOS/VS file name for more than one VM/370 may select the wrong minidisk.
running native, do
disk. Otherwise, If a program in the DOS/VS core image library may be executed in either
a DOS/VS virtual machine or under CMS/DOS, link edit the program with ACTION REL linkage editor control statement so that it uses the DOS relocating loader. DOS/VS ACCOUNTING This topic only applies when running DOS/VS Release 34 (or
earlier). It does nQ! apply when running either DOS/VS Release 34 with
the Advanced Functions-DOS/VS Program Product (5746-XE2) or DOS/VSE. Except with processors that have ECPS: VM/370 and virtual interval
timer assist, DOS/VS accounting gives inaccurate and inconsistent
elapsed processor times when operating under VM/370 with virtual machine
assist. This inconsistency occurs because the interval timer (located
at virtual storaqe lecation i'SO') used by the DOS/VS accounting
routine is only updated when VM/370 gets control. Therefore, when DOS/VS accesses the interval timer data, a variable amount of time may
have elapsed since VM/370 last updated the interval timer, and thus DOS/VS records an inaccurate processor time.
section 3. DOS/VS in a virtual Machine 73