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
address280 and a 3340 disk on virtual address 290 that correspond to
similar real devices on real addresses380 and 590, respectively.
BecauseDoth 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 aSTltC (store channel ID) instruction to virtual channel 2, V8/370 can simulate
it thesame 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 theOPTION statement in the
virtual machine's directory entry orby 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 simulatedSTltC instruction returns this information to the operating system: (1)
the modelnumber 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 specificationmay 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, whenV8/370 simulates the STltC instruction issued to the virtual block multiplexer channel, it gives
the operatingsystem 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 blockmultiplexer, the
operating system should not detect, or be affectedby, this
inconsistency.
For further restrictions about channel model-dependent functions,
refer toSPECIFYING 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 systemsmay 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
channel must correspond to real devices on real channels; the real
channels must be identical to each other in type and model. For
example:
address
similar real devices on real addresses
Because
channel (channel 2), the corresponding real devices
By meeting this requirement, when an operating system issues a
it the
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
virtual machine's directory entry or
channel can be a selector channel. In this case, the simulated
the model
be a block multiplexer channel. This specification
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
the operating
channel, not of a block multiplexer channel.
inconsistent with the channel's operation as a block
operating system should not detect, or be affected
inconsistency.
For further restrictions about channel model-dependent functions,
refer to
consoles. Operating systems
be routed to different consoles.
--or--