The second requirement means that all virtual devices on a virtual
channel must correspond to real devices on real channels; the real
channels must be identical to each other in type and model. For
example: Assume that a virtual machine has a 3330 disk on virtual
address 280 and a 3340 disk on virtual address 290 that correspond to
similar real devices on real addresses 380 and 590, respectively.
Because Doth virtual devices (280 and 290) are on a single virtual
channel (channel 2), the corresponding real devices (380 and 590) must both be on real channels that have an identical channel type and model.
By meeting this requirement, when an operating system issues a STltC (store channel ID) instruction to virtual channel 2, V8/370 can simulate
it the same way and return consistent results to the operating system.
Not only should the real channels be identical, but generally
speaking, they should be of the same type as the virtual channel. (The
virtual channel type is defined either in the OPTION statement in the
virtual machine's directory entry or by the class G CF DEFINE CHANNEL command.) Two exceptions to this general rule are: When the real channel is a block multiplexer channel, the virtual
channel can be a selector channel. In this case, the simulated STltC instruction returns this information to the operating system: (1)
the model number of the block multiplexer channel, and (2) a channel type field indicating that the channel is operating in selector mode. When the real channels are selector channels, the virtual channel can
be a block multiplexer channel. This specification may improve
performance when the virtual channel has devices on several real
selector channels. It allows the virtual machine to overlap channel
operations on the virtual channel and to take full advantage of the
several selector channels. However, when V8/370 simulates the STltC instruction issued to the virtual block multiplexer channel, it gives
the operating system the channel type and model number of a selector
channel, not of a block multiplexer channel. While this result is
inconsistent with the channel's operation as a block multiplexer, the
operating system should not detect, or be affected by, this
inconsistency.
For further restrictions about channel model-dependent functions,
refer to SPECIFYING VIRTUAL 8ACHINE CONSOLES To specify more than one console for a virtual machine, the virtual machine user must tell V8/370 about the existence of these additional
consoles. Operating systems may support either: -- where different classes of system messages can
be routed to different consoles.
--or-- Alternate consoles where the user can switch to a backup console wben-the-prIiary-console becomes inoperative. 14 IBM Operating Systems in a Virtual 5achine
To tell iM/370 about the existence of these consoles, either use
directory statements or issue CP commands. The way a user specifies the
second console depends upon whether: The user always wants to use a specific device at a specific IIC address.
--or-- The user wants flexibility in selecting which device or terminal is
to be used. !§Su!E1ion: An OS/VS virtual machine is to run its 3158 display console
at address 01F in display operator console mode. Also, the virtual machine is to operate a local 3270 terminal at address 1B8.
Generate OS/VS with at least two consoles: 01F as the primary
console, and 009 as the secondary console. Specify the secondary console by directory statement. Code it: CONSOLE 009 3210 using the i8/370 CONSOLE Specify the OS/iS primary console either by having a DEDICATE statement in the VM/370 directory or by using the CP ATTACH command after logon. Either specification allows OS/VS to use
the 3158 console in display operator console If the DEDICATE statement is used, then code it: DEDICATE 01F 01F If the ATTACH command is used, then, after logon, send a
message to the VM/370 operator that requests the following ATTACH command to be issued:
msg op attach 01f to userid as 01f To use any attached 3270 display terminal as the OS/VS primary
ccnsole in display operator console mode, either have a SPECIAL statement in the virtual machine's V8/370 directory entry or issue the CP DEFINE cOlllla nd af te r log on to VM/370. If the SPECIAL statement is used, it appears as follows: SPECIAL 01P 3270 If the SPECIAL statement is not used, assume that a local 3270 line
has been enabled by the VM/370 operator .• Then, issue the following
DEFINE command:
define graf 01f 3270 Section 1. General Considerations 15
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