3. The virtual=real machine operates in its allocated storage area with normal CCi translation in effect until the virtual machine
operator issues the CP command: SET NOTRINS ON this ti.e, all subsequent operations occur fro. the virtual CCWs in the virtual=real machine without translation. with BOTRINS on, the virtual machine must not perform I/O operations into page
zero or beyond its addressable limit. Is mentioned previously,
violation of this requirement can cause damage to the V8/370 system or to other virtual machines.
4. If the virtual=real machine performs a reset or IPL, the normal CCW translation routine regains control until the virtual machine
operator again issues the SET NOTRINS ON command. Only the
virtual=real machine operator can use the command. In operator message occurs if the virtual machine enters normal translation
mode.
The virtual=real option is used with programs or operating systems
that dynamically modify channel programs, or that wish to avoid CP
virtual channel program translation and paging degradation. If
virtual=real operation is desired, it must be specified at V8/370 system generation time. iirtual=real assigns the same real storage locations
to the virtual machine that exist on the real machine (except for page
zero, which is relocated). Por example, in Pigure 2, if a DOS system needs 160K bytes to run
virtual=real, CP puts all but the first 4096 bytes of the program at the
real storage address locations. Page 0 of the DOS supervisor is the
only part of the DOS virtual machine that can be relocated, and it
follows the last real page frame of the DOS machine. Pigure 2 also
shows that the major portion of the CP nucleus is permanently relocated
into upper storage (except for page zero) whether the virtual=real system is operating or not. The real page frame zero remains under
control of i8/370. CP dedicates 160K nonpageable bytes to the DOS machine. However, when the user no longer needs the virtual=real machine performance option and he logs off, the assigned virtual=real storage
can be reallocated as available pageable storage for use by other
virtual machines (assuming that no other users with the VIRT=REIL directory have need of the area). The reallocation of virtual=real
storage as usable and available storage for other virtual machines is
controlled by the UNLOCK command and the VIRT=REAL operand. Once the
pages are released, no virtual=real machine can be run unless V8/370 itself is reloaded. If more than one virtual machine needs the
capabilities of running virtual=real (at different times), V8/370 system generation parameters must specify the largest virtual machine that is
to run in the virtual=real environment. I more practical approach may be to generate a different version of V8/370 for each virtual=real machine, if the storage sizes are substantially different. 30 YM/370 Operatoris Guide

Real Storage Addresses
r--------------------------------------------------------512i----- VIRTUAL STORAGE POOL for other users RELOCATED CP NUCLEUS RELOCATED PAGE ZERO for the DOS aachine (locked in real storage)
156K DOS VIRTUAL=REAL KACHINE CP PAGE 0 Figure 2. DOS 160K Virtua1=Rea1 Storage Assignaents LOCKED PAGES OPTION 260K 164K 160K 4K
If sufficient page fraaes are available for other users, you can choose
to lock (fix) one or aore specific pages of a virtual aachine or the
pageab1e CP nucleus in real storage. This perforaance option differs
from the other options in that the LOCK command can apply to several
virtual machines. It is also possible to the reserved page fraaes
option apply to one user's virtual machine, and then have the lock
option apply to another user's virtual aachine. A locked page is
effective froa the tiae you invoke the lock option until the user logs
off the systea, or until you issue the UNLOCK co.mand. If the page or
pages that are locked have a high frequency of reference or change
activity, the lock option, like the reserved option, can cause an improvement in the user's virtual aachine performance or overall system performance because of the reduction in paging activity. Notes: ':---If a naaed systea currently has the locked pages option in effect,
reloading of the saae naaed system, loading of another systea, or a systea reset does not affect the locked· pages option of a
virtual The loading of named systems named systeas without using the UNLOCK coa.and beforehand results in pages
being made u,navailable for use if the first naaed syste. has locked pages in effect.
2. In an attached processor systea shared pages cannot be locked.
3. You should always prefer the reserved page frames option to the
locked pages option, if it is not already in use. The LOCK command locks specific pages into real storage regardless of activity, while
the reserved page frames option keeps all the currently aost active
pages in real storage.
section 2. Initiating V8/370 Operation 31