virtual machine is still run in dynamic address translation mode, but
since the virtual page address is the same as the real page address, no ccw translation is required. Since CCW translation is not performed, no
check is made to ensure that I/O data transfer does not occur into page
zero or any page beyond the end of the virtual=real machine's storage. Systems that are generated
system loader (DMKLDOOE). virtual=real system, see the with the virtual=real option use the
For information about generating a Figure 13 is an
virtual=real option.
example of a real storage layout with
The V=R area is 128K and real storage is 512K. Virtual Storage Addresses I CP PAGE 0 (MODULE DMKPSA) 4KI I Virtual Page 1 I I VIRTUAL=REAL AREA
/
/ SIZE = 128K BYTES I (Minimum size is 32K bytes.) 128KI OKI Virtual Page 4K, 132K, / REMAINDER OF CP NUCLEUS / , I I / DYNAMIC PAGING AREA
/ and I FREE STORAGE I I I I I I /
/ , I 0 I I I /
/ I I I /
/ I Real Storage Addresses OK 4K 128K
132K (DI1KSLC) End of CP Nucleus (DMKCPE) 512K (End of real
storage)
Figure 13. Storage Layout in a Virtual=Real Machine the
There are several considerations for the virtual=real option that
affect overall system operation:
1. The area of contiguous storage built for the virtual=real machine
must be large enough to contain the entire addressing space of the
largest virtual=real machine. The virtual=real storage size that a VM/370 system allows is defined during system generation when the
option is selected.
2. The storage reserved for the virtual=real machine can only be used
by a virtual machine with that option specified in the VM/370 directory_ It is not available to other users for paging space, nor
for VM/370 usage until released from virtual=real status by a
system operator via the CP UNLOCK command. Once released, VM/370 must be loaded again before the virtual=real option can become
active again. 96 Systeill

3. The virtual machine with the virtual=real option operates in the
preallocated storage area with normal CCW translation in effect until the CP SET NOTRANS ON command is At that time; wiTh several exceptions, all subsequent I/O operations are performed from the virtual CCwsin the virtual=real space without translation. The exceptions occur under any of the following
conditions: • SIO tracing active • First CCW not in the V=R region • I/O operation is a sense command • I/O device is a dial-up terminal • I/O is for a nondedicated device
(spooled unit record console virtual CTCA
or minidisks that are less than a full volume) • I/O device has an alternate path • Pending device status
Any of the above conditions will force CCW translation. Since
minidisks are nondedicated devices, they may be used by programs
running in the V=R region even though CP SET NCTRANS ON is in 4. If the virtual=real machine performs a virtual reset or IPL, then
the normal CCW translation goes into effect until the CP SET NOTRANS ON command is again issued. This permits simulation of an IPL sequence by CP. Only the virtual=real virtual machine can
issue the command. A message is issued if normal translation mode
is entered.
5. A virtual=real machine is not allowed to IPL a named or shared
system. It must IPL by device address. 6. When NOTRANS is in effect for a virtual=real machine. no meaningful
SEEK data is collected by MONITOR operations. AFFINITY This option allows virtual machines that operate on attached processor
systems to select the processor of their choice for program execution.
To select the affinity option, use the directory OPTION statement. or
specify the AFFINITY operand on the class A. B. F. or G SET command.
The directory OPTION statement is described in the The class A. B, and F SET commands are
described in the and the class G SET command is
described in the VML11Q fOf In application, the affinity setting of a virtual machine implies a
preference of operation to either (or neither) processor. Affinity of
operation for a virtual machine means that the program of that virtual
.achine will be executed on the selected or named processor. It does
not imply that supervisory functions and the CP housekeeping functions
associated with that virtual machine will be handled by the same
processor. Part 2. Control Program (CP) 97