April 1, 1981 FiguLe 10 illustrates a virtual transmission control unit running
remote 3270 units. When the terminals supported by the multiple-access system are not
those supported by as virtual operator consoles, the 'real line
appearances must be one of the following: • Defined in the VM/370 directory entry for the virtual machine via the
DEDICATE control statement; for example:
DEDICATE vaddr raddr
where: vaddr is the virtual address, and raddr is the real address of the--appropriate line appearance-on--the real transmission
control unit.
or -- • Attached to the virtual machine by an operator with privilege class
B; for example:
attach raddr to vml as vaddr
where: is the real address of the appropriate line appearance
on the real transmission control unit, and is the
address of the line appearance as generated in the virtual
machine operating system. .-- I I I I I , 1 I 1 I I I L- System/370 VM1 .----- I I I I '--- VM/370 Virtual 2703 ________________________________________---J Datal Set I Real 2703 communications Line '----------------------" , IData I Set '----_J 1 ----,
Data I Set I "'--- ___ ,J _...;.r-, ---. __ r"1 ------... ___ 13275 ___ I 3275 I J L- ___ J Figure 10. A Virtual 2703 TCU Controlling Remote 3270 Terminals 30 IBM VM/370 Operating Systems in a Virtual Machine

When virtual machine activity is initiated ?n an infrequent or basis, such as from a remote terminal a teleprocessing system, some (or all) of its virtual storage may be paged out before the
virtual machine begins processing. The paging activity required for the
virtual machine to respond to the teleprocessing request may increase
the time required to respond to the request. Use the locked pages or reserved page frames options to improve
performance.
If the Frogram must be run in the dynamic paging area, then locking
specific pages of the virtual machine into real storage may ease the
problem. However, besides page zero and the page containing the TF interruption handler, it is not always easy or possible to identify
which specific pages are always required.
A more flexible approach than locked pages is the reserved page
frames option. When a temporarily inactive virtual machine having this
cption is reactivated, these page frames are immediately available. If
the program code or data required to satisfy the request was in real
storage at the time the virtual machine became inactive, no paging
activity is required for the virtual machine to respond.
For details about the locked pages and reserved page frames options,
refer to the 2Y§1gm THE ASP VIRTUAL MACHINE When using the OS asymmetric multiprocessing system
installation find virtual machines useful in two ways. (ASP) , an
The first way, as shown in Figure 11, has a
can be run by two virtual machines eVM1 and
channel-to-channel adapter (CTCA).
virtual ASF system that VM2) using a virtual VM1 OS/ASP Main Processor I System/370 -----. VM2 I , r_-------, I I I I as/ASP Support Processor I I I I I I L- _____________ J I I Virtual eTC A
L ______________________ I I I , VM/370 I __________________________________________ J
Figure 11. Two ASP Virtual Machines Section 1. General Considerations 31