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 virtua1=rea1 machine's storage. Systems that are generated system loader (DMKLDOOE). virtua1=rea1 system, see the with the virtua1=rea1 option use the
For information about generating a 2yste! Figure 12 is an
virtua1=rea1 option. example of a real storage layout with
The V=R area is 128K and real storage is 512K. Virtual Storage Addresses I I CP PAGE 0 (MODULE DMKPSA) 4K I I Virtual Page 1 I I VIRTUAL=REAL AREA
/
/ SIZE = 128K BYTES I (!inimu. size is 32K bytes.) 128K, OKt Virtual Page
4K I 132KI / REMAINDER OF CP BUCLEUS / I I I / DYNAMIC PAGING AREA
/ and I FREE STORAGE i I I I I I /
/ I I 0 I I I /
/ I I I /
/ I Real Storage Addresses OK 4K 128K
132K (DMKSLC) End of CP Nucleus (DMKCPE) 512K (End of real
storage)
Figure 12. Storage Layout in a Virtual=Real Machine the
There are several considerations for the virtua1=rea1 option that
affect overall systea operation:
1. The area of contiguous storage built for the virtua1=rea1 aachine
aust be large enough to contain the entire addressing space of the
largest virtua1=rea1 machine. The virtua1=rea1 storage size that a VM/310 systea allows is defined during system generation when the
option is selected.
2. The storage reserved for the virtua1=rea1 aachine can only be used by a virtual aachine with that option specified in the VM/310 directory. It is not available to other users for paging space, nor
for VM/310 usage until released froa virtua1=rea1 status by a
systea operator via the CP UlLOCK co.aand. Once released, VM/310 aust be loaded again before the virtua1=rea1 option can becoae
active again.
CP Introduction 1-33

3. The virtual aachine with the virtual=real option operates in the
preallocated storage area with normal CCW translation in effect
until the CP SET NOTRAIS ON coamand is issued. At that tiae, with
several exceptions, all subsequent I/O operations are perforaed froa the virtual CCWs in the virtual=real space without
translation. The exceptions occur under any of the following
conditions: • SIO tracing active • First cew not in the V=R region • I/O operation is a sense co.mand • I/O device is a dial-up terminal • I/O is for a nondedicated device
(spooled unit record console virtual CTCA
or ainidisks that are less than a full volume) • Pending device status • I/O device has an alternate path
Any of the above conditions will force CCW translation. Since minidisks are nondedicated devices, they aay be used by prograas
running in the V=R region even though CP SET 10TRAIS 01 is in
effect. 4. If the virtual=real machine perforas a virtual reset or IPL, then
the normal CCW translation goes into effect until the CP SET ROTRANS ON coamand is again issued. This Feraits siaulation of an
IPL sequence by CP. Only the virtual=real virtual aachine 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 naaed or shared system. It must IPL by device address.
6. When NOTRAIS is in effect for a virtual=real aachine, no aeaningful SEEK data is collected by !ONITOR operations. AFFINITY This virtual machine option allows virtual machines that operate on
attached processor systems to select, if desired, the processor of their
choice for program execution. The selection can be aade by the V8/370 directory OPTION statement, or it can be made dynaaically by an operand
of the CP SET coa.and:
For class G users SET AFFINITY For class A users SET AFFINITY use rid
where nn is the processor address of the aain or the attached processor.
In application, the
preference of operation
affinity setting of a virtual aachine implies a
to either (or neither) processor. Affinity of
1-34 IBM VM/370 System Logic and Problem Deteraination--Voluae 1