Users can alternate between operating systems more simply if: • Devices used by both systems are supported at the same device
address.
--and-- • Common addresses are not used to support different devices.
If these two conditions are not met, the user must modify the virtual machine configuration before each IPL of a new system.
If the two systems require online typewriter keyboards at different
addresses, use the CP DEFINE command to change the address of the
virtual system console. For example: The as system (specified above)
requires an online typewriter keyboard at address 01F, while the ces system probably has its console at address 009. In this case, issue
this command before loading 230:
cp define 009 as 01f
Because CMS automatically communicates with any valid multiplexer
address, a user can leave the console at 01F and satisfy both systems. If the systems expect different device types at the same address, the
coamon address must be assigned to the appropriate device each time a new system is loaded. If CMS is running with a disk at address 191 and
os is generated to support a 3330 at that address, issue the following
command before loading os:
cp detach 191
An appropriate device can then be added to the virtual machine at
address 191. Add the device either before loading or in response to a mount request from the os system. For direct access storage devices, this procedure is necessary
even if both systems support the same device type at the same address.
Except for VSAM disks, the disk format used by ces is unique. It is not compatible with that of other operating systems. Files can be shared between CMS and as or DOS only through VM/370 spooling or through VSle data sets. MULTIPLE-ACCESS VIRTUAL MACHINES Multiple-access programs execute in a virtual machine and directly
centrol terminals. These terminals do not have to be supported by VH/370 as virtual operator consoles, but they may be of any type
supported by the virtual machine. These programs use lines that are
either dedicated to the virtual machine (by the directory entry) or
assigned to the virtual machine dynamically.
For example: Figure 5 shows two multiple-access systems (controlled
by virtual machines VM1 and VM2). While each system controls real 3277s
by using part of the real 3272, the real 3272 appears to both virtual machines as though they each have sole control of it. (The virtual
system consoles of VM1 and VM2 are not shown.)
26 IBM VM/370 Operating Systems in a Virtual Machine

Real
3277 V111 r-----. i I I L __ ----.J VM2 Control Program of VM/370 virtual
3272
Real
Real
3277
J I Virtual I 3272
3272
Real
3277 r---- I Real I 3277
Note: Users can define virtual lines for a virtual machine. running a 3704 or 3705 in Network Control program (NCP)
lines are a subset of the lines controlled by a real
control unit (TCU). Figure 5. Virtual Devices: Local 3270 Terminals
Except when
mode, these
transmission
Except when running a 3704 or 3705 in NCP mode, a subset of the lines of a real transmission control unit (TeO) can be defined as virtual
lines for a virtual machine, as shown in Figure 6. VM1 r-----, I I I I I I VM2 Control Program of VM/370 Virtual 2703 I Virtual I 2703 L-- ________________ . ________ Data Set Real 3705
(In 2703 Emulation Mode) Data Set Note: Two lines on the real 3705 are defined as virtual lines for two vIrtual machines named VM1 and VM2. The remaining lines may support
virtual operator consoles.
Figure 6. Virtual Devices: Remote Terminals Section 1. General Considerations 27