When using the DEDICATE statement to attach a 2305 to a
virtual machine, both the real and virtual addresses must refer to the
first base device address on the unit. The first base address of the 2305 is 0 or 8 --the resulting address appears as xxO or xxB. However, when VM/370 processes the statement, it creates all eight addresses (0-7 or 8-F) for the 2305. The LINK control statement has no unique considerations for running an
operating system in a virtual machine. Use the SPECIAL control statement to add I/O devices that do not require
corresponding real devices. Some examples are: magnetic tapes,
channel-tc-channel adapters, pseudo timers, communication lines, and
devices that, while available to the System/370, are not supported by VM/370. Installaticns can use the SPECIAL control statement to specify a
virtual transmission control unit for a multiple-access operating
system. For example: If the system requires three communication lines
from a 2703, specify: SPECIAL 061 2703 IBM SPECIAL 062 2703 IBM SPECIAL 063 2703 TELE
Before a terminal can communicate with a multiple-access system, the
terminal user must issue the DIAL command:
dial userid to connect to any available line port; or issue:
dial userid 062 to connect to a particular line. Of the three lines specified in the foregoing example, one was a
teletypewriter line and two were IBM terminal lines. When the DIAL command is issued with no specific address, VM/370 connects the terminal
to any available line as defined in the SPECIAL control statement; the
line then belongs to the specified userid. If no lines are available or
if all lines are busy, VM/370 issues an error message ana does not make
the connecticn. To droF a dialed line, a user must issue the CP RESET command. Section 1. General Considerations 45
DEFINING VIRTUAL DEVICES When using the SPOOL, DEDICATE, and SPECIAL control statements to define
virtual devices, specify virtual addresses that do not conflict or
ccntend with the virtual control unit interface. conflict or
contention occurs because devices can require special I/O interface
protocol frem control units, such as for shared and nonshared subchannel
operations. Putting devices that require different real control units
on the same virtual control unit can result in a hung or busy condition.
To avoid this problem, users must define (and separate) devices within
their own control unit range.
For example: If the directory entry specifies: SPOOL 102 3211 SPECIAL 103 3270 the control unit 0 on channel 1 controls both an unshared device (the
3211 printer) and a shared device (the 3270 display unit). processing
of channel prcgrams involving these two devices can result in a hung or
busy condition. AUTOLOG FACILITY AUTOLOG is a convenient way to initiate large production operating systems with many I/O devices that run under VM/370. The I/O devices
needed by these operating systems require considerable contiguous
storage space for the I/O control blocks established by Vft/370. When these large operating systems are started after other, smaller users
have been using V8/370, the contiguous storage space may not be
available. When there is insufficient contiguous space, the logon of the
virtual machine is successful; however, there may be an insufficient
number of I/O devices to run the operating system and its application
programs.
To ensure sufficient contiguous storage space, log on those virtual machines after loading V8/370. Have the V8/370 system operator issue the CP AUTOLOG command before
enabling user terminals. Define the AUTOLOG1 virtual machine in the VM/370 directory. The AUTOLOG1 userid can be used to logon and load virtual machines that
require substantial contiguous storage.
Before enabling user terminals, the V8/370 system operator can issue the CP AUTOLOG command for each production virtual machine that requires
substantial contiguous storage. The directory entry for the userid
indicated by the CP AUTOLOG command must contain an IPL statement for
the desired operating system. For more information about the CP AUTOLOG command, refer to the 46 IBM VM/370 operating Systems in a Virtual
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